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STEP'UP PhD Congress 2025
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Europe/Paris
IPGP
IPGP
1 rue Jussieu 75005 Paris
Description
A Cosmos in Motion :
From the Primordial Explosion to the Present and Future Dynamics of the Universe and Planets
We would like to inform all speakers that each talk will last 15 minutes (10–12 minutes for the presentation and 3–5 minutes for questions). Please make sure to time your presentation accordingly so as not to exceed the allotted time. Presentation materials must be uploaded to the CDD website no later than the day before your talk. You can upload your presentation as a speaker by going to your abstract submission, clicking "Edit", and attaching a file. Please use PDF format preferably.
For those presenting a poster, the required format is A0, in either portrait or landscape orientation, as you prefer. Posters must be displayed on Thursday the 22nd in the designated rooms (please check with the helpdesk upon arrival). They may remain on display throughout the day but must be collected before 6:00 PM; otherwise, they will be discarded by our team.
Wednesday conference slides
Contact
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1
Opening speechOrateur: Prof. Marc Chaussidon (IPGP)
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Charting the Cosmos: Waves, Particles, Stars and Life: CDD-01 1/2
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2
Keynote 01: Alain RiazueloOrateur: Alain Riazuelo (IAP)
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3
How to measure ripples in the fabric of space time ?
The Laser Interferometer Space Antenna (LISA) space based gravitational wave detector is set to be launched in the mid 2035's to be placed 66 000 000 km away from Earth and act as a low frequency GW observatory in space.
LISA will measure gravitational waves in the low frequency regime, ripples in the fabric of space time that are caused by the acceleration of massive objects in space and time. LISA will be measuring the low frequency part of these emissions meaning that it will probe much heavier objects than ground based detector such as LIGO and VIRGO can detect.
This observatory will take the form of a constellation of three satellites that fly in a triangular configuration with a length baseline of around 2 500 000 km. A distance measurement will be done using heterodyne interferometry that will track movements between the satellites up to a precision of 10 picometers (achieving a relative measurement of 10^-21).
Such an instrument must be thouroughly tested before being sent to orbit, but with such a complexe measurement scheme one cannot just turn on the instrument to check if it works and meets the required specifications. For this reason, France is developing a complex test system to check that the instrument can meet the required sensitivity.
For my contribution, I will first explain the basic functioning of this future observatory and how we manage to perform this highly challenging measurement. For the second part of this contribution, I will give an overview of how we are going to be testing the instrument before sending it to space.
Orateur: Maxime VINCENT (AstroParticule et Cosmologie) -
4
Probing Inflation with PICO: Simulations and Delensing for CMB B-Modes
Since its discovery in 1965, the cosmic microwave background (CMB) has been a cornerstone of our standard big bang cosmological model. Space- and ground-based experiments have precisely measured the CMB’s intensity fluctuations across the sky and are improving measurements of its polarization. A current science objective is to search for the signature of an inflationary period that is thought to have occurred a fraction of second after the big bang, and that could have left an imprint on the polarization of the CMB.
The polarized CMB signal can be decomposed into parity-even E-modes and parity-odd B-modes. The inflationary signal would manifest itself as a B-mode signal. However, the signal is exceedingly faint, only one part in 100 million relative to the nearly uniform glow of the CMB, and finding it requires precise subtraction of confusing foregrounds, which have much larger amplitude. One such foreground are B-modes generated by distortion of E-modes into B-modes, a process called 'lensing'. Accounting for and removing this foreground is called 'delensing'.
PICO - the Probe of Inflation and Cosmic Origin - is a proposed NASA space mission that has been endorsed for implementation by the US Astro2020 Decadal Panel. Its data will give the most sensitive probe for B-mode inflationary signal. I will describe my contributions to developing the mission through conducting simulations and validating the efficacy of delensing.
PICO report NASA
Foreground separation and constraints on primordial gravitational waves with the PICO space mission JCAPOrateur: Julien Tang (Université Paris Cité) -
5
Modeling gamma-ray signatures of particle acceleration in stellar clusters from GeV to PeV
A couple of classes of astrophysical objects such as young massive stellar clusters (YMSCs) have recently emerged as promising galactic PeVatron candidates, potentially explaining the knee of the cosmic-ray spectrum as alternative to isolated supernova remnants (SNRs). Meanwhile, the LHAASO observatory is the first to effectively probe the photon detection band above 0.1 PeV, that can correspond to multi-PeV hadronic cosmic rays. Thus, it enables the use of its gamma-ray data, combined to other complementary detectors such as HESS or Fermi-LAT, to constrain galactic particle acceleration models and parameters. It can also help for trying to identify the contribution from the different categories of galactic accelerators to the observed cosmic ray flux, especially towards the PeV domain.
In this context, we model the escape and transport of cosmic rays from their acceleration site to nearby molecular clouds or clumps, where proton-proton interactions producing high-energy gamma rays occur. Our focus is on scenarios where the source is a YMSC, with particles being accelerated at shocks (either wind termination shocks or embedded SNRs) before escaping into the interstellar medium. Using a semi-analytical approach, we explore the conditions (e.g., source-cloud distance, time, injection slope, number of stars) required to produce a gamma-ray excess above the sensitivity of the detectors. This allows us to identify the parameter space where such a signal could be observed and, consequently, to determine which cluster-cloud systems are viable candidates for producing such an excess. Finally, we compare model predictions with gamma-ray data to refine key acceleration parameters, such as the wind termination shock efficiency or the injection spectrum. Additionally, we investigate whether some of the so-called dark PeVatrons detected by LHAASO could be explained by star cluster–cloud systems.
Orateur: Alexandre Inventar (APC Laboratory) -
6
InterGalactic Magnetic Fields and Gamma-Ray Bursts with CTAO
The InterGalactic Magnetic Field (IGMF) is believed to be a remnant of the Big Bang and the origin of cosmological magnetic fields. However, it has yet to be detected. In this context, the Cherenkov Telescope Array Observatory (CTAO) will have the potential to place competitive constraints on the IGMF by analyzing data from Active Galactic Nuclei (AGN) and Gamma-Ray Bursts (GRBs). In this study, we propose to simulate CTAO observations of the few GRBs detected in the TeV range, using its available instrument response functions, as well as realistic observation conditions. The expected IGMF signatures are modeled with a dedicated simulation code, and the analysis of the synthetic data is performed using a joint spectral and temporal fit. By assuming a power-law behavior in energy with an unknown cut-off, we will extrapolate the detected GRBs into the tens of TeV energy range. We will show that CTAO can constrain the IGMF in the range $[10^{-19} \, \text{G}, 10^{-15} \, \text{G}]$ for various coherence lengths and place limits on fields stronger than $10^{-15}$ G.
Orateur: Ténéman Keita (CEA Paris-Saclay)
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2
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7
Movie - The Fire Within: A Requiem for Katia and Maurice Krafft
Screening of a documentary film in the Cuvier amphitheatre.
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17:00
Ice Breaker Buffet
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1
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10:00
Breakfast
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Charting the Cosmos: Waves, Particles, Stars and Life: CDD-01 2/2
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8
Foundation-like models for Astroparticle Physics Experiments
ADAPT [Accelerate Discoveries (boosting) Astroparticle Physics (analysis) Techniques] is the intent to apply machine learning algorithms onto event data from astroparticle physics experiments, to offer an alternative and faster analysis procedure, compared to the computational intense and lengthy classical state-of-the-art algorithms.
The main focus of the project lies in the possibility to learn a latent space of all events of an experiment in an unsupervised way. In this latent space, each event can be represented trough a self-learned set of important features. It can therefore be used to build a “Foundation” model, that can later be efficiently fine-tuned on a specific regression or classification task. The advantage of this unsupervised approach, with respect to a supervised optimization for a specific task, is that the latent space contains, due to its self-learned nature, event descriptions that are richer in information.
The nature of recorded data in many astroparticle experiments can be best described as the mathematical object of a graph. The natural choice is therefore to use graph neural networks, to analyse these data structures.
Such a model is then trained unsupervised as a masked auto-encoder, yielding the ability to map each node, but also the full graph in a latent space, and by this providing a compressed information representing an intermediate step for further analysis.The current goal of the project is to identify and separate the signal in the presence of high levels of environmental background, with the aim to extract the final graphs containing only the physical event of interest. The use case presented here is within the KM3NeT experiment.
Orateur: Maximilian Eff (APC (Laboratoire Astroparticule & Cosmologie), Université Paris Cité) -
9
Innermost stable circular orbit of comparable-mass compact binaries at the fourth post-Newtonian
We compute by means of post-Newtonian (PN) methods the innermost stable circular orbit of comparable-mass compact binaries. Two methods are used with equivalent results: equations of motion in harmonic coordinates and Hamiltonian formalism in ADM coordinates.
Orateur: Etienne Ligout (APC) -
10
Is turbulent convection the only exciting mechanism of acoustic modes in solar-like oscillators?
The solar convective envelope generates, by dynamo effect, a surface magnetic field whose strength evolves on an 11-year cycle, with a change in polarity at the end of each cycle. A similar magnetic variability exists in other solar-type stars, influencing their dynamics. Furthermore, solar-like oscillators experience acoustic modes whose properties, such as their frequency, amplitude and energy vary over time in relation to the activity cycles. The turbulent motions in the convective envelope of these stars were so far considered as the only mechanism for exciting the modes. In this work, we investigate the variation of mode excitation during Cycles 23, 24, and the beginning of Cycle 25 for the Sun. To do so, we analyze data obtained since 1996 by the VIRGO SunPhotometers on the SoHO satellite, using a method that provides a better time resolution than classical methods such as peakbagging. By combining the small-time-scale variations in energy for several low-degree modes, we found a statistical discrepancy in the observed excitation rate compared to the one expected under the hypothesis that modes are only stochastically excited by convection. Our results indeed show that several modes can be excited at the same time. During this presentation, we will explore the possible sources of high energy in the modes, i.e. instrumental problems or other exciting mechanisms, which may be linked to the magnetic cycle of the star, such as flares or Coronal Mass Ejections, and compare the results with data from the GOLF spectrometer, also carried by SoHO.
Orateur: Eva Panetier (Université Paris Cité, Université Paris-Saclay, CEA, CNRS, AIM) -
11
Spectrum of a Cold Exoplanet around a White Dwarf
The study of the atmosphere of exoplanets orbiting white dwarfs is a largely unexplored field. With WD 0806-661 b, we present the first deep dive into the atmospheric physics and chemistry of a cold exoplanet around a white dwarf. We observed WD 0806-661 b using JWST's Mid-InfraRed Instrument Low-Resolution Spectrometer, covering the wavelength range from 5 to 12 μm, and the Imager, providing us with 12.8, 15, 18, and 21 μm photometric measurements. We carried the data reduction of those data sets, tackling second-order effects to ensure a reliable retrieval analysis. Using the TauREx retrieval code, we inferred the pressure–temperature structure, atmospheric chemistry, mass, and radius of the planet. The spectrum of WD 0806-661 b is shaped by molecular absorption of water, ammonia, and methane, consistent with a cold Jupiter atmosphere, allowing us to retrieve their abundances. From the mixing ratio of water, ammonia, and methane we derive C/O = 0.34 ± 0.06,
, and N/O = 0.023 ± 0.004 and the ratio of detected metals as a proxy for metallicity. We also derive upper limits for the abundance of CO and CO2 (1.2 × 10−6 and 1.6 × 10−7, respectively), which were not detected by our retrieval models. While our interpretation of WD 0806-661 b's atmosphere is mostly consistent with our theoretical understanding, some results—such as the lack of evidence for water clouds, an apparent increase in the mixing ratio of ammonia at low pressure, or the retrieved mass at odds with the supposed age—remain surprising and require follow-up observational and theoretical studies to be confirmed.Orateur: Maël Voyer (UPC / CEA) -
12
High-time-resolution analysis of X-ray data from Proxima Centauri
The study of X-ray and extreme ultraviolet (together, XUV) emission from stars is recently experiencing a renewed interest in the fields of star-planet interactions and habitability. The presence of an atmosphere is usually considered a requirement for habitability and XUV fluxes are a main concern when trying to establish whether a planetary atmosphere will fade away with time. Particular attention is given to M dwarfs stars, as they present long-term flaring activity, and the habitable zone (HZ) for these stars are really close. This imply that HZ planets around them may experience really high XUV fluxes during their lifetime. A thoughtfully analysis of XUV emission from M dwarf and their flaring behavior is a needed input for atmospheric modeling. Proxima Centauri represents one of the best candidates for in-depth studies of XUV radiation because it is the closest star to us and presents high activity. We have analyzed archival data of Proxima Centauri from the XMM-Newton and Chandra telescopes, and produced temporal series of its X-ray emission. We have paid special attention to calibration and time-resolution. We propose an original simplified pile-up correction and find that, depending on the treatment of this instrumental effect, fluxes of radiation with energy between 0.1 and 12.0 keV may vary by up to 30%. We report also strong dependence on the energy. We propose a time-binning algorithm that allows to reach a time resolution of up to 90s. The quiescent and the flaring emissions from Proxima Centauri are characterized both in energies and in frequencies using nearly 6 days of observations spanning 19 years. Luminosities in the 0.1 - 12.0 keV energy range are presented with uncertainties less than 10% and average time-resolution of 5 minutes.
Orateur: Andrea Damonte (CEA - INAF) -
13
Validation of the Euclid Catalogue of Galaxy Clusters with external data
The Euclid spacecraft was launched in July 2023 to the Earth-Sun Lagrange point L2. The mission will produce one of the largest galaxy cluster catalogues withtens of thousands of clusters over the 15 000 square degrees of its extragalactic sky survey. This catalogue will need to be validated with external data, in order to check for newly discovered clusters, to prepare analyses of cluster multi-wavelength scaling relations, and to characterize the Euclid selection function. In preparation, we used the Dark Energy Survey (DES) Y1 RedMaPPer catalogue as surrogate for the Euclid catalogue to put in place our validation procedures with different millimeter, optical, and X-ray surveys . We used two complementary matching methods to find counterparts for clusters in position, but also in redshift. These methods will be explained with the example of crossmatches between RedMaPPer and the SRG eROSITA catalogue, which contains a large sample of X-ray clusters in the western Galactic hemisphere.
Orateur: Anaïs Widmer
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8
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12:00
Lunch
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Conferences: How research is organized in France (and other countries)?Président de session: Sébastien Charnoz
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14:30
Break and discussion with Sebastien Charnoz
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Conferences: Designing objective figures and avoid color bias in sciencePrésident de session: Laure Manceau (IPGP)
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15:30
Break and discussion with Laure Manceau
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Conferences: How to write a successful grant proposal?Président de session: Benoit Ivanovsky
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16:00
Break and discussion with Laure Manceau
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16:00
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16:30
Break and discussion with Benoit Ivanovsky
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10:00
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09:30
Breakfast
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Exploring Surfaces and Skies: Planets, Moons, and Earth: CDD-02
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14
Sulfur isotope anomaly in the Ryugu asteroid
Ivuna-type carbonaceous chondrites (CI) have
geochemical compositions similar to the solar
photosphere. Their sulfur (S) isotope composition might
thus reflect the average nebular gas. However, most CI
chondrites have undergone sulfur oxidation on Earth.
This may introduce a bias for the determination of S
isotope ratios of the bulk nebula, as sulfide oxidation
causes sulfur isotope fractionation. In contrast with CI
meteorites, samples collected by the Hayabusa2 mission
from the Ryugu asteroid have never interacted with an
oxygen-rich atmosphere. They offer a unique
opportunity to determine the S isotope ratio of CI
objects.
Using wet chemistry and isotope ratio mass
spectrometry, we determined the S speciation and
isotopic composition of the A0481 Ryugu sample and of
a series of CI chondrites. We found CI meteorites to
have 4.5 ± 0.5 wt.% S on average, consistent with
previous estimates. Sulfur is mostly carried by oxidized
components such as sulfates and elemental sulfur (S0).
The Ryugu sample contains 4.5 ± 0.1 wt.% S, similar to
bulk CI meteorites, although S occurs mostly as sulfides.
No sulfates were detected, but we found about 10 ± 3
% of the S in the Ryugu sample to occur as elemental
sulfur.
The S isotope compositions of sulfides, sulfates and
S0 in CI meteorites largely reflect a pattern of sulfide
oxidation. Wether oxidation occurred in Earth or on the
parent bodies is not clear. In contrast, Ryugu sulfides
show unfractionated δ34S values, consistent with
minimal oxidation. The S isotope ratios of the Ryugu S0
is also inconsistent with being produced by sulfide
oxidation. Of all samples measured here, only the S0
from Ryugu exhibits small but resolvable Δ33S and Δ36S
anomalies. We argue that it represents a component
associated with photochemistry in the nebular gas. In
Ryugu, that component has not been erased by the
meteorite weathering that other CI have undergone.Orateur: Margot Debruycker (IPGP) -
15
Detection of Body-wave Reverberations on Titan and Implications for the Ice Shell Structure Constraint
NASA's upcoming space mission, Dragonfly, selected as the 4th mission under the New Frontiers Program, is set to explore Saturn's icy moon, Titan, in the mid-2030s. The mission's goal is to assess Titan's potential habitability. The rotorcraft lander, designed like a drone, will be equipped with the DraGMet instrument package, enabling comprehensive geochemical, climatic, meteorological, and geophysical analyses across multiple sites on Titan's surface. A key instrument in this package is the DraGMet SEIS short-period vertical seismometer, developed by JAXA, which will play a crucial role in investigating Titan’s internal structure.
For successful seismic observations, it is essential to first anticipate the type of events and seismic phases that are likely to be observed in the data, with their detection conditions. Titan’s surface exhibits a variety of potentially endogenous geological formations, many of which were identified through SAR data from the Cassini-Huygens mission (2004-2017), and some further analyzed with global tidal stress field models. As a first step, we focus on one of the primary sources of seismic activity in icy ocean worlds, “ice cracking events”, caused by Saturn’s tidal forces. We model the broadband seismic waveforms produced by such events, considering several internal structure models and anelastic attenuation scenarios.
These results are then incorporated into noise models—considering both atmospheric turbulence and experimentally evaluated instrumental noise—to derive constraints on the detectability of these signals. We will also discuss methods for constraining a homogeneous upper internal structure case based on observations—particularly in estimating the thickness of Titan's ice shell.Orateur: Lorraine Delaroque (Institut de Physique du Globe de Paris, U. Paris Cité) -
16
Modelling SEP and GCR Atmospherics showers with Monte Carlo Simulations
Modelling SEP and GCR Atmospherics showers with Monte Carlo Simulations
Keywords: Atmospheric modelling, Radiation monitoring, High Energy physics, Monte Carlo Methods
With the growing use of integrated electronics, the impact of natural atmospheric radiations is becoming a prominent concern for both space, where the environment is more severe, and atmospheric applications (i.e. aeronautics and surface level), where natural shielding is higher, but more systems are exposed. The radiative environment is also subject to local variations like the Van Allen belts shown in Fig. 1, where high energy protons and electrons are trapped. Moreover, discrete space weather events can momentarily increase particle flux and energy in orbit. As for the atmospheric environment, complex interactions between Solar Energetic Particles or Galactic Cosmic Rays with the magnetosphere and atmosphere of the Earth can create large scale atmospheric showers, eventually reaching commercial flight levels or even the ground itself.
Because of the physical scale and complexity of such phenomena, we developed a large scale Monte Carlo simulation using the Geant4 C++ toolkit. This simulation computes the propagation of high energy particles within the magnetosphere and the atmosphere, from the exobase down to the surface level, as well as interactions with the ground and the resulting albedo emission.In this presentation, we will discuss SEP and GCR models, the impact of radiations on electronics systems, as well as the Monte Carlo simulation code methodology and first results.
Orateur: Leo Favier (Nucletudes, AIM/CEA-IRFU) -
17
Study of the impact of sources of variability on the mineralogical characterization of soils by hyperspectral imagery
This work aims to improve hyperspectral image processing methods for the identification and quantification of soil minerals. These methods allow the radiometric signal measured for each pixel of the image to be interpreted in terms of physico-chemical properties. Due to the limited spatial resolution of the images, the reflectance spectrum corresponding to a given pixel is generally a mixture of supposedly pure spectra from different materials known as endmembers. In practice, endmember spectra are not unique due to matrix effects such as surface moisture content or grain size, and the measurement configuration that may change from one scene to another [1].
Two main families of models are used to process hyperspectral images: physics-based models [2] and data-driven models [3]. Physics-based models make it possible to understand the spectral variability of the data, but they require knowledge of the intrinsic optical properties of the soil components, which are generally unknown. Data-driven models seek correlations between reflectance spectra and the physico-chemical properties of soils, but their “black box” nature often makes them difficult to interpret and to generalize to different contexts.
This work combines the advantages of physics-based and data-driven models in order to improve the interpretation of hyperspectral imagery with respect to different sources of spectral variability. Emphasis will be placed on matrix effects due to soil moisture content and grain size, which are among the most important and constraining sources of variability in soil mineralogical composition analysis. We will study their impact on absorption band parameters (amplitude, position, shape, asymmetry, etc.) of minerals obtained by spectral deconvolution methods. In particular, we will analyze the detection limits of the absorption bands of certain minerals of interest as a function of soil surface moisture.[1] Borsoi R.A., Imbiriba T., Bermudez J.C.M. et al. (2021), Spectral variability in hyperspectral data unmixing: A comprehensive review, IEEE Geoscience and Remote Sensing Magazine, 9(4):223-270.
[2] Dupiau A., Jacquemoud S., Briottet X. (2023), Reflectance of wet natural soils in the solar domain: contributions and limitations of physical models, in Radiometry of wet surfaces. When water matters (L. Simonot, Ed.), EDP Sciences, pp. 11-26.
[3] Chen J., Zhao M., Wang X. et al. (2023), Integration of physics-based and data-driven models for hyperspectral image unmixing: A summary of current methods, IEEE Signal Processing Magazine, 40(2):61-74.
Orateur: M. Corentin Feray (PSS) -
18
Towards near-real time monitoring of volcanic deformation and lava flow using Capella SAR images
Syn-eruptive monitoring of volcanic deformation and surface changes is crucial for timely hazard assessment. Spaceborne Synthetic Aperture Radar (SAR) can reliably provide visually-interpretable images of volcanic edifices at high spatial resolution during day and night, regardless of the weather conditions. Yet, most traditional change detection methods only work between SAR images acquired by the same sensor with the same observation geometry, preventing revisit times of less than several days.
Here, we present a novel method for detecting and measuring syn-eruptive topographic changes on a sub-daily basis using (i) Capella Space high-resolution SAR images acquired with varying geometries during the eruption, that we compare with (ii) a high-resolution Digital Elevation Model acquired years before the eruption. The syn-eruptive SAR amplitude image is correlated against a synthetic image generated from a radiometric terrain model combining the knowledge of the SAR sensor geometry and pre-eruptive topography. The cross-correlation score is used for lava flow mapping, which enables to track the progress of lava flows over time with daily or even sub-daily temporal resolution. Estimated offsets between real and synthetic images provide two independent components of the ground displacement field (in the line-of-sight and in azimuth). Combining multiple images acquired with different viewing geometries gives access to the three components of the displacement field. We apply the method to the Piton de la Fournaise volcano, validating the results against ground-truth data from the OVPF observatory, including daily-resolved lava flow maps produced from traditional approaches and GNSS displacement vectors from permanent and campaign stations.
Orateur: Arthur Hauck (IPGP - UPCité) -
19
Keynote 03: From Insight on Mars to Farside Seismic suite on the Moon : how Planetary seismology discovers the seismicity and interior of terrestrial bodiesOrateur: Prof. Philippe Lognonné (Institut de Physique du Globe de Paris, U. Paris Cité)
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14
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12:00
Lunch
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Posters: Posters 1/2
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20
Dynamics of magma reservoir before and after volcanic eruptions at the Axial Volcano in the Eastern Pacific using time-lapse seismic imaging method
Magma reservoirs (mixture of liquid melt, crystals, and gases) are normally present beneath most active volcanoes from where dikes initiate, and magma erupts to the surface. Depending upon the thermal state of the reservoir, magma may be in a pure melt state if supplied by fresh melt from below, or in a mush state because of cooling by hydrothermal circulation, which increases the crystal fraction in the magma (Singh et al., 1998). The magma is most likely to erupt when it is in a pure melt state, less likely when it is in a mush state. Thus, the nature of the magma reservoir (pure melt versus mush) plays a crucial role in the occurrence of volcanic eruptions and the intensity of the hydrothermal circulation above. Whereas it has been difficult to characterize the nature of magma reservoirs on land due to poor imaging conditions, the marine environment allows more favorable imaging conditions.
The Axial Volcano in the Eastern Pacific Ocean is a large submarine volcano that hosts many hydrothermal vent fields and has erupted three times (1998, 2011 and 2015) in recent years. As a result, it has been the subject of extensive geological and geophysical studies over the last 30 years, including setting up of a permanent, real time, wired-to-shore, multiparameter seafloor observatory (Kelley et al., 2014), and a three-dimensional (3D) multi-channel seismic survey (Arnulf et al., 2019; 2020). Interestingly, 2D seismic reflection data were acquired in 2002, 2012 and 2019 before and after the 2011 and 2015 eruptions, hence these data could be used to characterize the dynamic behavior of magma reservoir before and after the eruptions in a time-lapse sense.
The time-lapse signal could be due to the change in depth of the top of magma reservoir and/or a change in the state (melt versus mush) of the magma. In this study, we apply AVO techniques to monitor the state of a magma reservoir over time, before and after eruptions. We processed three vintages to remove the effect of the data acquisition footprint and to compute the differences between the three data vintages. Key time-lapse 2D seismic processing techniques employed include deghosting, wavelet shaping, amplitude scaling and time shift. To enhance the imaging of AML-reflected waves, we also implement several conventional processing steps such as trace editing, trace interpolation, common midpoint (CMP) sorting, band-pass filtering, predictive deconvolution, normal moveout (NMO) corrections, frequency–wavenumber (f-k) filtering, and stacking. A partial stacking approach is used to assess changes in the magma reservoir across the three seismic vintages.
In the next step, we will perform AVO modeling to compute the P-wave and S-wave reflection responses for various states of the magma lens—ranging from pure melt to fully crystallized magma, in order to better understand the temporal evolution of the magma reservoir and assess its eruption potential as of 2019.
Orateur: Yan Zhao (IPGP-TE) -
21
Potential of Fluid-Mantle Interactions for Abiotic Organic Synthesis on Oceanic Transform Faults
Recent studies have highlighted the presence of aromatic amino acids (Ménez et al., 2018) and solid organic compounds (Sforna et al., 2018; Andreani et al., 2023) in mantle rocks exposed along the Mid-Atlantic Ridge. These organic compounds were formed abiotically - without the involvement of life - through the reduction of inorganic carbon (e.g., CO2) by geogenic hydrogen (H2) during fluid-rock interactions. As fundamental building blocks of more complex organic molecules, which are potential precursors to life, these organic compounds strengthen the hypothesis of a hydrothermal origin of life. In this context, the extent and the impact of lithospheric alteration on the associated carbon cycle and organic chemistry of prebiotic interest remain critical to understand. Interestingly, research on transform faults (OTFs), which are strike-slip faults that segment mid-ocean ridge segments, has revealed that these plate boundaries could be also hydrothermally active with deep hydration reaching depths of up to 25 km (Prigent et al., 2020) and percolation of C-rich fluids in the fault zone (Klein et al., 2024). These findings suggest that OTFs could also be favorable environments for abiotic organic synthesis of potential prebiotic interest on Earth. To assess this potential, petrological and geochemical analyses were conducted on peridotite mylonites from two OTFs on the ultraslow Southwest Indian Ridge, deformed and emplaced at the seafloor from very high temperature/depth on the fault zone (~1000°C).
Hydrated silicate phases (e.g., amphibole) are associated with deformation and serve as indicators of fluid-rock interactions. Trace element concentrations suggest that the fluids that inter acted with studied mantle rocks had a hydrothermal origin, even at great depths on the fault zone.
Fluid inclusions (FIs), which are micro-cavities that trapped a portion of the fluids circulating through fractures, also formed during deformation. The majority of these FIs have been observed in olivine. The formation of FIs is constrained to high temperatures, near the brittle-ductile transition of olivine (~800°C), which allows the mineral to fracture and then heal. These FIs were analyzed through Raman spectroscopy and FIB-SEM cross-sectioning. Results show that all the fluids within the inclusions had reacted with the surrounding mineral to form various crystalline and gaseous phases, among which many carbon-bearing phases with different speciation (e.g., carbonate, organic carbon, including methane, and carbonaceous compounds).
Our results thus indicate a complex carbon dynamics and the first evidence for endogenic organic carbon compounds in an OTF context formed during interaction of deforming mantle rocks with hydrothermal fluids at high temperature. Although these results are promising, questions still need to be addressed regarding the source of inorganic carbon, the composition of hydrothermal fluids percolating into the mantle of OTFs, their impact on the carbon cycle, the mechanisms of organic compound formation, and the roles of magmatism, hydrothermalism, deformation, and temperature in these processes.
Orateur: Suzanne JOANNO (Institut de Physique du Globe de Paris) -
22
Tsunami-Induced Ionospheric disturbances: détection challenges and methodological approaches
Tsunamis are one of the most destructive natural hazards causing heavy human losses. They can be generated by submarine earthquakes and/or volcanic eruptions and landslides) and it is almost impossible to forecast their impact.
A near-real-time monitoring of tsunamis is required for population’s safety. Differents methods are currently used to monitor tsunami propagation in both near field (<500 km from the source) and far-field (>500 km away the source) like seafloor pressure sensors, DART and tide gauges. However, most of tsunamigenic areas are still not instrumented and the monitoring remains very challenging. An alternative approach would be to use the ionosphere, the upper layer of the atmosphere, in order to detect tsunamis and monitor their propagation. Tsunamis propagation generate internal gravity waves that can be detected in the ionosphere within 20-60 minutes after they are generated at the ocean surface. By using measurements of total electron content (TEC) from GNSS-receivers, one can detect co-tsunamic ionospheric disturbances (TTIDs), and estimate tsunami parameters based on analysis of TTIDs’ characteristics.
However, numerous disturbances can travel in the ionosphere and can mask the TTIDs. Therefore, monitoring tsunami propagation requires a method for detecting ionospheric perturbations, separating those induced by tsunamis from others, and determining spatio-temporal features of TTIDs. The first step in this development is to create a collaborative database containing the TTID information recorded by GNSS receivers. This contribution will present our newly developed strategy for detecting tsunamis from the ionosphere, and the challenges to overcome.
Orateur: Clélia MARÉCHAL (Program) -
23
Noble gases in Archean hydrothermal quartz: Tracers of mantle geodynamics and xenon atmospheric escape
The composition of the Earth's atmosphere is an archive of the geological history of our planet. Noble gases are excellent tracers of processes like atmospheric escape, mantle outgassing, allowing estimates of Earth's ancient geodynamics [1,2]. For example, the atmospheric 20Ne/22Ne ratio has evolved through degassing of solar neon from the mantle in an originally chondritic atmosphere [3,4,5]. Thus, measuring the isotopic composition of paleo-atmospheric Ne offers a new method for estimating the outgassing history of the Earth's mantle. Recently, a model published by [3] proposed a 20Ne/22Ne ratio of 9.75 at 3.3 Ga, <1% lower than the modern one (9.808). Atmospheric xenon has also undergone significant changes since the Archean. The modern atmosphere is mass-dependent fractionated relative to the Archean atmosphere, with an enrichment in heavy isotopes and a depletion of the light ones. Another Xe feature of the modern atmosphere is its elemental depletion relative to cosmochemical references. This Xe paradox can be explained by a specific atmospheric escape of ionized Xe over time, inducing a Xe-rich atmosphere in the Archean and thus an evolution of the 130Xe/84Kr elemental ratio over time [6]. Thus, measuring this elemental ratio in the Archean atmosphere can provide strong evidence of this scenario.
Some hydrothermal quartz sampled ancient atmospheric components during their formation [7,8]. The atmospheric signal is never pure and reflects a mixture between paleo-atmospheric gases and noble gas isotopes produced in the crust. In this study we measured the elemental and isotopic composition of noble gases released from fluid inclusions trapped in Archean hydrothermal quartz (2.7 Ga-old, Fortescue Group in Australia; 3.3 Ga-old, Barberton in South Africa) to derive an Archean atmospheric 20Ne/22Ne ratio and a Xe/Kr ratio. Noble gases have been released by step-crushing, purified and measured using a Noblesse mass spectrometer.
Ne released from ancient quartz defines two distinct mixtures between an atmospheric component and nucleogenic Ne produced in the crust, with high 21Ne/22Ne ratios (up to 0.0717 ± 0.0014 1σ). The mixing line allows us to derive a 20Ne/22Ne ratio between 9.808 and 9.815 at 3.3 Ga and between 9.766 and 9.808 at 2.7 Ga has been retrieved (at 21Ne/22Ne=0.029). These results suggest that a modern-like value was already reached 3.3 Ga-ago, arguing for a strong outgassing activity of the mantle in the first billion year of Earth's geodynamical history.
The mixture between paleo-atmospheric Xe and Xe produced in the crust, allows us to determine a 130Xe/84Kr ratio at 3.3 Ga of 2.2 times the modern one, consistent with an enrichment in Xe during the Archean compared to the modern atmosphere.[1] Catling & Kasting (2017) Atm. evol. on inhabited and lifeless worlds. Cambridge Univ. Press. [2] Ozima & Podosek (2002) Noble Gas Geochem. Cambridge Univ. Press. [3] Zhang et al. (2023) EPSL 609, 118083. [4] Marty et al. (2012) EPSL 313-314, 56-66. [5] Marty et al. (2022) Icarus 381, 115020. [6] Zahnle et al. (2019) GCA 244, 56-85. [7] Pujol et al. (2011) EPSL 308, 298-306. [8] Avice et al. (2023) EPSL 620.
Orateur: M. Felix Vayrac (IPGP) -
24
Redox Transfer at Sub-Arc Mantle: Insights from Petrology and Transitional Metal Stable Isotope (Fe, Zn, Cu) Geochemistry of Orogenic Peridotites
The mantle wedge above subduction zones is often considered more oxidized (i.e., exhibiting higher oxygen fugacity (fO₂)) than other mantle domains due to metasomatism by slab-derived fluids. Garnet peridotites from subduction zones, for instance, record oxygen fugacities that are 3–4 log units higher than those of garnet peridotite xenoliths from the sub-cratonic mantle. However, no direct link has yet been established between the fO₂ record and the transfer of redox-sensitive components (e.g., SO₄, CO₂) from the subducted slab to the mantle wedge, and the fate of subducting oceanic lithosphere remains poorly constrained.
In this study, we undertake a detailed petrologic and geochemical characterization of garnet peridotites from Ulten zone and Adula-Cima-Lunga unit (Alpe Arami, Cima di Gagnone, and Monte Duria) that equilibrated at different P-T conditions. We present high precision in-situ synchrotron Mossbauer source Fe3+ measurements on major and metasomatic minerals (garnets, clinopyroxenes and amphiboles) in the peridotite samples. The results enable us to model the fO2 record and constrain the redox reactions occurring during fluid/rock interactions in the context of subduction. Additionally, the trace element and non-traditional stable metal isotope (Fe, Zn & Cu) geochemistry data of the samples provide crucial clues regarding the tranfer of redox sensitive elements in subduction zones, and also give more information on the geodynamic origin of the studied peridotites. Thus, we attempt to correlate the redox record of the sub-arc mantle, using Fe3+ measurements at the mineral scale, and whole-rock geochemical data, in order to characterize the relative effects of subduction-fluids on the composition and oxidation of the mantle wedge peridotites .Orateur: Ruksana Rose (Università degli Studi di Milano Bicocca, Milano, Italy & Université Paris Cité, Institut de physique du globe de Paris, CNRS, Paris, France) -
25
A model of the magnetic field generated in the magnetosphere derived from ground observatory data
The geomagnetic field observed at the Earth's surface or at satellite altitudes is the result of a combination of signals generated by both internal and external sources. Internal sources include magnetic fields produced by the geodynamo in the Earth's outer core, as well as fields generated by magnetized rocks in the lithosphere and induced magnetic fields within the lithosphere and mantle. External sources of the magnetic field are located in the ionosphere and magnetosphere, and are driven by electric currents. In this presentation, we outline an approach to extract and model the magnetospheric field contributions using magnetic observatory vector measurements. These data have a high temporal resolution and are particularly well-suited to characterize magnetospheric signals in space over a wide range of time scales. The goal of this work is to reliably characterize these signals from 1996 to 2024, during geomagnetically quiet times, spatially up to spherical harmonic degree 6, with a temporal resolution in time of one hour. For this, we apply an approach that uses a combination of the Kalman filter and correlation-based techniques. This method offers a more robust statistical framework, providing more accurate error estimates for the model parameters. We evaluate the model's key features using standard criteria, such as fit to the data, posteriori model distribution, shapes of power spectra over time, spatiotemporal geographical variations and correlations with geomagnetic indices like the Disturbed Storm Time (Dst) and the magnetospheric ring current (RC) indices. A Fourier analysis of the models shows the expected semi-annual, monthly, and daily harmonics, but also evidences of tidal signals.
Orateur: Yalei SHI (PhD student at IPGP) -
26
Automatic Detection and Localization of earthquakes from the ionosphere via co-seismic ionospheric disturbances
Submarine Earthquakes can trigger large tsunami waves, causing major risks and potentially disastrous consequences on coastal communities. It is therefore essential to assess the tsunamigenic potential of an event by determining its characteristics (magnitude, location, and surface displacements). However, providing accurate early warnings in the case of deep ocean earthquakes remains challenging when relying exclusively on seismic data. Besides seismic waves, earthquakes and surface motions can also generate acoustic waves that propagate to high altitudes, inducing fluctuations in the ionospheric plasma density known as CoSeismic Ionospheric Disturbances (CSID). These perturbations provide valuable insights into the source mechanisms and can contribute to complement the limited ground stations distribution along the oceanic faults. This, in turn, supports the establishment of accurate detection and localization techniques in Near-real-time (NRT).
In this study, we introduce a new method for the automatic detection and localization of earthquakes from ionospheric Total Electron Content (TEC) observations. We first estimate the detection probability of a CSID first arrival through a deep learning model, we then apply a migration-stacking procedure to perform the inversion. In order to address uncertainties in detection altitude, acoustic velocity models, and to account for prior knowledge on seismic source location and origin time, we employ a Bayesian framework. The resulting posterior distributions of source parameters can then be computed within a few minutes in a CPU cluster making it near-real-time applicable.Orateur: Mlle Ines Dahlia Ouar (Université Paris Cité / Institut de Physique de Globe de Paris (UPC/IPGP)) -
27
Detailed Three-dimensional Fault Model of the 2022 Mw 6.6 Luding Earthquake, Sichuan: Implications for Potential Seismic Risk in Southeastern Tibetan Plateau
The detailed 3D fault model and further seismic rupture behavior analysis and fault mechanics simulation based on it are important and meaningful. A strong Mw 6.6 earthquake occurred in Luding, Sichuan, on 5 September 2022, the epicenter was located near the Moxi segment of the Xianshuihe Fault Zone (XSHF) in southeastern Tibetan Plateau. This earthquake is also situated at the Y-shaped junction of the XSHF, the Longmen Shan Fault Zone (LMSF), and the Anninghe Fault Zone (ANHF). Two seismic gaps, one in the southern LMSF and the other in the northern ANHF, are widely considered to have high seismic risk in this region. To date, a detailed 3D fault model has not been established for this earthquake, preventing a 3D Coulomb stress change (ΔCFS) calculation for further seismic potential analysis. Therefore, we build a detailed 3D fault model of the earthquake area and compute ΔCFS in the surrounding areas. Based on 3D modeling technology, we establish a 3D model of the main faults in the Luding earthquake area using previously published relocated earthquake catalog and focal mechanism solutions; including the Moxi segment (f1) of the XSHF, the Daduhe fault (f2) and two previously unknown faults (f3 and f4). We then calculate 3D ΔCFS, and find that the mainshock of the Luding earthquake significantly increased the Coulomb stress near the epicenter and triggered two M > 5 aftershocks. Moreover, it caused a remarkable increase in Coulomb stress and hence a notable enhancement in seismic hazard in the northern ANHF, where the fault has remained strongly coupled since 1480 CE and has been approaching the next strong earthquake recurrence.
Orateur: Fang Xu (State Key Laboratory of Earthquake Dynamics and Forecasting, Institute of Geology, China Earthquake Administration, Beijing, 100029, China / Universite Paris Cite, Institut Physique du Globe de Paris, CNRS, Paris, France) -
28
Fault Structural Complexity and Rupture Characteristics of the 2021 Maduo Earthquake
Earthquake rupture processes, occurring across multiple spatial and temporal scales from surface to depth, reveal critical information about the nature of seismic events. Such insights are essential for understanding earthquake nucleation mechanisms, assessing seismic hazards, and interpreting regional tectonic deformation. Since the Cenozoic collision between the Indian and Eurasian plates, numerous large active fault systems around the Tibetan Plateau have been reactivated, resulting in frequent moderate to large earthquakes. The 2021 Maduo earthquake, the largest in China since the 2008 Wenchuan earthquake, occurred on the Jiangcuo Fault, a secondary fault within the northeastern Bayan Har block. This highlights the event's unique seismogenic context and complex rupture behavior.
In this study, we applied fractal dimension analysis of coseismic slip and used deep learning techniques to automatically identify surface ruptures from UAV imagery. Our results show that the spatial variation in rupture density, orientation, and style is strongly influenced by fault structural complexity. The densest surface ruptures are observed in the southeastern segment of the rupture zone, where the fault exhibits significant bending and supershear rupture characteristics. In contrast, regions with relatively simpler fault geometries exhibit sparser rupture patterns. Geophysical and geodetic inversion results indicate that the structural complexity of the Jiangcuo Fault extends from surface traces into the seismogenic depth, generating heterogeneous stress accumulations (asperities and barriers) that modulate the rupture process. Dynamic rupture modeling further demonstrates the critical role of fault segmentation, tectonic prestress, and geometric irregularities in controlling rupture evolution.
Future work will focus on the dynamic rupture simulation of the 2001 Kokoxili earthquake, aiming to explore its rupture characteristics and the associated dynamic interactions with surrounding fault systems. These efforts will contribute to a more comprehensive understanding of rupture behavior within the complex fault networks of the Tibetan Plateau.
Orateur: Xin Liu -
29
Improving gamma spectrometry for radionuclide analysis of lunar and Martian regolith samples
With the return of lunar material from the Chang’E 5 and Chang’E 6 missions and the upcoming Mars Sample Return mission, developing optimized methodologies for analyzing rare and highly valuable samples of regolith is essential. These samples offer unique insights into the physical and geochemical evolution of planetary bodies. Among the tools available for studying these processes, natural radionuclides—such as uranium, thorium, potassium, and their decay products like radon (Rn-222) play a key role. Radon, in particular, is a sensitive tracer of volatile transport, outgassing events, and regolith dynamics on airless bodies such as the Moon and Mercury. It also informs us about thermophysical properties and geological histories, contributing to our understanding of planetary surface evolution.
To support this scientific effort, we have developed a high-sensitivity gamma-ray spectrometry methodology at the Laboratoire National Henri Becquerel (LNE-LNHB) tailored to the analysis of very low-mass extraterrestrial samples (~1 g). A custom gas-tight sample holder was designed to minimize gamma-ray self-attenuation in the low-energy range, preserve radon within the sample, and ensure inert conditions to avoid alteration of pristine material. The setup relies on a high-purity germanium detector equipped with an active anti-coincidence veto system, optimized to reduce background noise and improve detection limits, particularly for low-energy emissions such as the 46.54 keV line of Pb-210.
As a validation step, a Martian regolith analog (JSC Mars-1) was enclosed and measured immediately to minimize radon loss. The total acquisition time was 36.25 days, allowing for precise quantification of the natural gamma-emitting radionuclides. The measured specific activities were 65.0 ± 11.7 Bq/kg for U-238, 19.7 ± 7.5 Bq/kg for Ra-226, 13.6 ± 4.9 Bq/kg for Th-232, 1.12 ± 0.4 Bq/kg for U-235, and 146 ± 47 Bq/kg for K-40. A specific treatment was also applied to investigate the unsupported Pb-210 fraction, enabling future interpretations of radon emanation from planetary regoliths.
This methodology demonstrates the capability to perform radiological characterization of extraterrestrial materials using non-destructive techniques that require minimal sample mass while achieving high sensitivity. Beyond analytical performance, this approach contributes to the broader understanding of volatile dynamics, surface processes, and interior-surface interactions on planetary bodies. It offers a valuable tool for future exploration missions and provides a bridge between geochemistry, planetary science, and environmental physics, disciplines united by the need to decode the motion and evolution of a cosmos in constant change.
Orateur: M. Íñigo de Loyola Chacartegui Rojo (Commissariat à l'énergie atomique et aux énergies alternatives) -
30
Investigating the Tectonic Complexity of the Bulnay-Tsetserleg Fault Junction in Mongolia Using a Temporary Seismic Network
Mongolian tectonics is shaped by the far-reaching effects of the Indo-Eurasian collision, which drives deformation and stress over 2000 km behind the Himalayan front. During the 20th century, Mongolia experienced four earthquakes with magnitudes greater than 8, making it an exceptional location for studying intraplate seismicity, predominantly with strike-slip components. Among these events, the Tsetserleg-Bulnay fault system recorded the largest intraplate earthquake doublet, with two magnitude 8 earthquakes occurring 14 days apart in 1905, rupturing more than 500 km of fault. The surface rupture, remarkably well-preserved due to the region's low erosion rate, has enabled extensive paleoseismic investigations. Despite this, the junction between the two faults remains unclear at the surface, and the fault structures at depth are still poorly constrained, leaving the interactions between fault segments not well understood.
In the present day, the significant microseismic activity affecting the Bulnay and Tsetserleg faults is anomalous given the low regional deformation rate and overall Mongolian seismicity. This persistent microseismicity could be interpreted as aftershocks that illuminate the faults’ structures more than a century later. By tracking this microseismicity with precision, we aim to map the faults’ 3D geometry at depth and address the key questions: how do these faults interact, why did the Bulnay earthquake occur only 14 days after the Tsetserleg earthquake, and why is its epicenter located 150km west of the junction zone?
In 2024, the French Atomic Energy Commission (CEA) and the Mongolian Institute of Astronomy and Geophysics (IAG) collaborated to strategically deploy a temporary seismic network, TDBnet, at the Bulnay-Tsetserleg junction. This network, comprising 10 geophones in addition to 5 broadband stations, operated altogether for five months, complementing the national network, and recorded local seismicity with unprecedented resolution. The collected data are being processed to automatically detect seismic phases using state-of-the-art methods, including the PhaseNet artificial neural network implemented in Seisbench. The detected events are then precisely located using an absolute location method, followed by an absolute relocation corrected with a Source Specific Station Time approach as proposed in the NonLinLoc-SSST framework. We present the experiment along with preliminary results, including a precisely determined earthquake epicenter map.
Orateur: Laure Manceau (CEA IPGP) -
31
Microbial community responses to repetitive heating and cooling in high-temperature aquifer thermal energy storage
Storing seasonal energy in the subsurface using High-Temperature Aquifer Thermal Energy Storage (HT-ATES) can significantly reduce the energy consumption and greenhouse gas emissions of the heating sector. Compared to conventional ATES, which operates at lower temperatures (25–30°C), HT-ATES can store water heated up to 90°C. While higher temperatures improve efficiency, they also induce significant thermal and biogeochemical changes in the reservoir.
Elevated temperatures alter geochemical equilibria, affecting groundwater composition, mineral stability and overall water quality. While geochemical impacts of HT-ATES have been thoroughly investigated, the effects of repeated thermal fluctuations on aquifer microbial communities and functions remain poorly understood. Microbial activity can influence groundwater chemistry, mineral dissolution and precipitation, enhance clogging through biofilm formation or accelerate corrosion of infrastructures. Better understanding these mechanisms, particularly via groundwater sampling, laboratory experiments and field tests (push pull tests), is essential to tackle operational and environmental challenges.
In this framework, the Horizon Europe PUSH-IT project (https://www.push-it-thermalstorage.eu/) is aiming to demonstrate the feasibility of large-scale high-temperature heat storage solutions through six pilot and demonstrator sites in order to generalise their utilisation throughout Europe. One demonstrator site, located in TU Delft (Delft, Netherlands), will be a HT-ATES well storing water up to 90°C.
We first monitored the groundwater in order to describe the initial biodiversity of the aquifer before any heat storage process and gain insight on the natural baseline. In parallel, various microbial sampling, preservation and analysis methods were performed and tested to help future monitoring efforts.
Secondly, the effects of temperature variations induced by this HT-ATES on microbial communities in the reservoir are characterized by simulating HT-ATES conditions in the laboratory using a pressurised flow-through cell with BRGM’s high-temperature high-pressure BioREP platform. Groundwater from the TUDelft monitoring well is injected through aquifer sediments with cyclic temperatures ranging from ambient levels to 90°C. A first phase of inoculation of the sediments takes place for three months with continuous circulation of groundwater at the aquifer’s ambient temperature of 12°C. Following steps expose sediments to series of thermal cycles to gain insight into reservoir processes. Geochemical parameters (pH, redox potential, conductivity, key redox-sensitive compounds) and microbial community composition (qPCR, 16S rRNA Illumina sequencing) in both water and sediments are monitored over time to track their evolution in response to temperature variations.
In the last stage of the project, the microbial diversity evolution will be monitored under conditions more representative of the final storage process, during an initial hydraulic and thermal pumping test (hot push-pull test).
Acknowledgements: Funded by the European Union under grant agreement 1011096566 (PUSH-IT project). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or CINEA. Neither the European Union nor CINEA can be held responsible for them.Orateur: Maud Watkinson -
32
Numerical Simulation Insights into the impact of tidal stress on seismicity
Earthquakes result from the accumulation of stresses in the Earth's crust. Tidal stress is typically a few kilopascals, with primary components having periods of about 12 and 24 hours. Observational studies show that slow earthquakes are sensitive to tidal stress (Rubinstein et al., Science, 2008; Nakata et al., NG, 2008; Thomas et al., Nature, 2009), while the effect of tidal stress on ordinary earthquakes remains debated (Vidale et al., JGR, 1998; Tanaka et al., JGR, 2002; Ide et al., NG, 2016). Here, we investigate how small tidal stress can modulate seismicity (earthquakes and slow slip events) within the framework of rate-and-state friction.
We focus on two key questions regarding tidal modulation of seismicity: First, can tidal stress induce earthquakes on stable sliding faults? Second, how does tidal stress modulate the timing and magnitude of earthquakes on unstable faults with stick-slip behavior?
To explore these questions, we perform simulations using spring-slider model with rate-and-state friction and the aging law, considering typical tidal stress perturbations on normal stress for stable sliding faults (k = 1.1 kc) and unstable faults (k = 0.9 kc).
It has been found that for stable sliding faults, as the perturbation amplitude ratio increases, stable sliding transitions to single periodic oscillations. Further increase in amplitude leads to larger and more complex oscillations. In addition, resonance phenomena have been observed (Perfettini et al., GRL, 2001). At a perturbation amplitude ratio of 0.1%, the slip rate increases by about 5 times as the perturbation period nears the resonance period. At a perturbation amplitude ratio of 1%, slow slip events are generated, but no earthquakes occur. For unstable faults, the effect on earthquakes is very small at realistic tidal perturbation amplitude ratios. These results suggest that tidal stress may enhance slip rate, leading to local stress accumulation, which indirectly promotes slow slip events, or directly increase local stress, triggering slow slip events. However, under the given conditions, the effect of tidal stress on earthquakes is negligible.
We also further investigate the continuum two-dimensional fault model with a velocity-weakening zone surrounded by velocity-strengthening zones, focusing on the effect of tidal stress on the nucleation of both earthquakes and slow slip events, thereby extending and validating the results obtained from the spring-slider model above.Orateur: YIshuo ZHOU (LG_ENS) -
33
Peering into the Planet : Novel Tools for Modelling Seismic Waves and Imaging Earth’s Interior
Accurate models of the Earth's interior are essential not only to satisfy scientific curiosity but also to serve society, given their immediate applications and practical significance. Seismic waves remain our most powerful window into the Earth's interior, yet both the modeling of wave propagation and the interpretation of seismic data present significant challenges. Numerical methods, for instance, are often either computationally expensive and complex or simplistic and limited in accuracy. In addition, the inherent reliance on existing Earth models can constrain our ability to resolve absolute velocity structures. Overcoming these challenges is crucial for advancing our understanding of deep Earth.
This work addresses these challenges on two fronts: theoretical and observational. On the theoretical or numerical side, I develop one- and two-dimensional elastic wave propagation models using Radial Basis Functions (RBFs), a mesh-free numerical method that has gained prominence in recent years for its exceptional flexibility and precision in simulating elastic wave propagation in complex, heterogeneous media. RBFs are particularly well-suited for modeling wavefields in irregular geometries, allowing for high accuracy without the need for a structured grid. One of the persistent challenges in numerical simulations is the generation of parasitic waves due to the use of point sources, which are modeled as Dirac delta functions. These point sources, while convenient mathematically, introduce high-frequency noise that contaminates the primary wave signals. To address this, I use binomial filters at source locations, which approximate the Dirac distribution more smoothly and reduce parasitic waves. This technique improves both the spatial and temporal accuracy of the seismic waveforms without increasing computational costs.
On the observational front, I apply the recently developed Virtual Receiver Approach (VRA), a technique that leverages travel-time differences between closely spaced seismic stations to directly estimate local absolute velocities, independent of assumed Earth models. This independence from pre-assumed velocity structures provides a unique opportunity to investigate deep Earth features with minimal bias. While previous applications of VRA have successfully imaged the intricate structures of the Pacific Large Low Seismic Velocity Province (LLSVP), my work extends the application of this method to a new, yet-to-be-specified region of Earth’s interior. This extension aims to uncover new velocity anomalies that could provide insights into previously unexplored territories and compositional variations at depth.
This work combines refined numerical simulations with model-independent observational techniques to improve seismic imaging of Earth’s interior. The dual approach not only enhances the reliability of seismic interpretations but also opens new possibilities for global deep Earth studies and hence further ongoing geophysical studies.
Orateur: Mlle Chahana Nagesh (IPGP, U. Paris Cité) -
34
Photogeodesy : GNSS, Acoustic and Photogrammetric fusion for underwater centimetric positioning
GNSS/Acoustic technology enables the measurement of absolute horizontal seafloor displacements through repeated surveys of acoustic beacons over several years. However, a key limitation of this approach is that the beacons must remain underwater for extended periods.
In this study, we explore an alternative method that combines photogrammetry and GNSS/Acoustic techniques to determine the absolute positions of distinct seafloor features, such as rocks, outcrops, or shipwrecks. Our approach utilizes an Autonomous Underwater Vehicle (AUV) equipped with a high-resolution digital camera capable of capturing overlapping, near-vertical images with sub-centimeter pixel resolution. The AUV's trajectory is managed using multiple Uncrewed Surface Vessels (USVs), which are geolocated with GNSS systems.
This method produces orthorectified images of the seafloor that may still exhibit internal deformations and limited georeferencing accuracy. To address this, we incorporate a temporary GNSS/Acoustic system deployed during the photogrammetric survey. Acoustic beacons are used as ground control points to correct internal distortions within the photogrammetric model and to accurately anchor it to an external reference frame with centimeter-level precision.
In this poster, we present the current status of our project and highlight several key challenges that need to be addressed to operationalize this innovative approach.
Orateur: Hugo Reveneau (CNRS) -
35
Studying eccentric supermassive black hole binaries in PTA
Pulsar Timing Array (PTA) observations are carried out to search for
gravitational waves (GWs) in the nano-Hertz band. The most plausible
source is the population of supermassive black hole binaries emitting
GWs that incoherently superpose and form a stochastic GW background
(SGWB). In addition, particularly massive and nearby SMBHBs produce
strong signals that may stand out above the GWB and be individually
resolvable. PTAs will see the early inspiral of these systems observed
at large orbital separations, where the orbital evolution may be
strongly influenced by dynamical interactions with the environment,
through which SMBHBs may retain a significant eccentricity.
In this poster, I will present a gravitational waveform model based on
the Effective-One-Body (EOB) approach. We use it to search for eccentric
binaries in the data collected by EPTA collaboration. We verify the
efficiency of the search and its limitations using simulated PTA data.
In particular, we focus on disentangling a continuous GW signal from a
binary from SGWB. Evaluating our ability to detect and correctly
characterise eccentric binaries is an essential step in analysing and
interpreting results based on EPTA and IPTA data, which, in turn,
impacts our understanding of the properties of the SMBH population in
the local Universe.Orateur: Sara Manzini (APC - Université Paris Cité) -
36
The 2021–2022 Alboran-Al Hoceima Seismic Swarm: Seismic Relocation, Fault Reactivation, and the Role of Mantle-Derived Fluids
The Alboran-Al Hoceima region is a tectonically complex active zone, marked during the last decades by several major earthquakes (1994, 2004, 2016) and series of seismic swarms that reveal diverse triggering mechanisms. These mechanisms are driven by a combination of evolving mantle-lithospheric processes, tectonic forces, and fluid interactions. The prolonged 2021–2022 seismic swarm, marked by a maximum magnitude of M 5.3, exhibited a distinct fluid-driven behavior. Our integrated analysis, using double-difference relocation techniques (HypoDD) with a regional seismic velocity model (CSEM Iberia 2019), applied to seismic bulletins from both sides of Alboran sea, reveals clear migration patterns. The diffusivity analysis indicates a rapid initial episode, with values reaching approximately 14 m²/s, followed by a decline to more stable and slower migration rates ranging between 3.47 and 8.10 m²/s. The swarm activity was primarily clustered along the southern tips of the Alboran Ridge and the Al-Idrissi Fault Zone, extending southward offshore where it connects east of Ras-Tarf The spatial distribution of seismicity also suggests a notable linkage to a newly identified fault F1. Focal mechanism solutions from key events, indicate transtensive strike-slip faulting. The geometry of seismicity, spanning depths from 0 to 50 km, shows a strong correlation with low-velocity anomalies, shallow Moho depths, and the presence of recent Neogene volcanic structures, support the involvement of mantle-derived fluids in fault reactivation. This swarm contrasts sharply with earlier seismic sequences, including the 2016 (Mw 6.4) and the 2004 Al Hoceima (Mw 6.3) earthquakes, whose larger-magnitude mainshocks reflect more mature fault behavior. The spatial progression of seismicity, shifting from burst-like to prolonged activity reveal varying underlying driving mechanisms, illustrates the movement of deformation fronts. These variations point to a regional transition towards a distributed plate boundary, with swarm behavior acting as a proxy for lithospheric fragmentation. The recurrence of distinct swarm types over two decades provides valuable insights for understanding seismic cycles in the Alboran region.
Orateur: Hamza Akka (Laboratoire de Géologie - UMR8538, École Normale Supérieure – PSL, CNRS, Paris) -
37
Tracing subducted carbon cycling by potassium isotopes of carbonatites
Carbon cycling between Earth's surface and mantle reservoirs is crucial for maintaining planetary habitability. However, a significant yet poorly constrained aspect is the extent to which crustal carbon can withstand devolatilization during subduction, thereby influencing the deep Earth's carbon budget. Carbonatites offer an invaluable record to investigate this issue. Here, we present high-precision potassium isotope data from a comprehensive collection of carbonatite samples from continental and oceanic settings, spanning the last two billion years. Our modeling indicates that the enriched (heavy) potassium isotopic signatures observed in carbonatites originate from their mantle sources rather than magmatic or post-magmatic processes. These results provide compelling evidence for a robust link between oceanic crust subduction and the recycling of carbonates into the mantle sources of carbonatites. Consequently, our findings strongly support the hypothesis that subduction of carbonate-rich altered oceanic crust has served as a critical mechanism for transferring carbon into Earth's deep interior throughout geological history.
Orateur: Zhengyu Long (IPGP)
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20
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Shaping the Earth: Faults, Quakes, and Erosion: CDD-03 1/2
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38
Keynote 04: From paleoseismology to space geodesy, can we still discover a new tectonic plate? Example along the Dead sea fault.Orateur: Yann Klinger (IPGP)
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39
From thermal pressurization to dilatant strengthening during stick-slip ruptures on saturated saw-cut thermally cracked westerly granite
Earthquakes result from the transient frictional weakening of faults during co-seismic slip. Dry faults weaken due to the degradation of fault asperities by frictional heating (e.g. flash heating). In the presence of fluids, theoretical models predict faults to weaken by thermal pressurization of pore fluid. Despite theoretical predictions, not only numerical models seldom consider the Pressure-Temperature dependence of the fluid properties, but experimental data is also scarce on rock-fluid interactions during dynamic rupture under realistic stress conditions. This study seeks to elucidate how fluid thermodynamic properties influence the respective roles of thermal pressurization and flash heating in fault weakening.
Here, dynamic stick-slip events (SSEs) were experimentally produced under low and high pore fluid pressure conditions on samples of Westerly granite, previously heat treated to enhance their permeability. To investigate the mechanisms driving frictional weakening, fluid pressure was directly monitored on and off the fault during SSEs using in-situ pore fluid sensors. Acoustic emissions, both amplified and unamplified, provided microseismic counts, location, magnitude and rupture velocities of each SSE. The post-SSE temperature was assessed using Raman spectroscopy on a carbon layer deposited along the fault surface.
Preliminary experimental results highlight the transition from thermal pressurization (TP) to dilatant strengthening (DS) and off-fault damage depending on the stress regime. At low shear stress and compaction stage, TP was observed as a coseismic increase in pore fluid pressure for each SSE. On the contrary, in the later stages of our experiment, at higher shear stress accompanied with dilatancy, SSEs were preceded by a pre-seismic drop of on-fault pore fluid pressure, followed by a large coseismic one. Off-fault pore fluid pressure showed a slight increase throughout all SSEs. Strain responses in the sample bulk exhibit unique patterns: dynamic dilatancy followed by dynamic compression during early SSEs, and static dilatancy followed by dynamic compression during later SSEs. Rupture velocity inversions predominantly indicate supershear characteristics. Finally, the slow transition between TP and DS was accompanied by a long phase during which only slow stick-slip ruptures were observed. The mechanism underlying this inversion and the role of fluid pressure behaviors on fault weakening remains to be analyzed.
Eventually, key physical and seismic parameters derived from the experiments will inform numerical models, which will be compared against thermal pressurization theory—adjusted to account for fluid thermodynamic property dependencies—and extrapolated to crustal depths (~2–10 km) where natural earthquake nucleation typically occurs.Orateur: M. Caiyuan FAN (École Normale Supérieure, Paris) -
40
Synthetic earthquakes in a 3D numerical sandbox
This study presents a numerical sandbox experiment in which earthquakes occur. The experiment models a strike-slip fault by enforcing translation motions to the bottom and lateral boundaries of a virtual, rectangular box. The approach used is the Discrete Element Method (DEM), where rock is modelled as a set of spherical, rigid particles interacting with one another.
The geometry of the fault is not prescribed but emerges spontaneously when the applied boundary conditions shear the initially homogeneous, intact material. As shearing continues, oblique, Riedel shears form and progressively coalesce, until they give birth to a more mature through-going fault. This fault retains geometric complexity, with traces of the earlier Riedel structures still apparent.
Throughout the fault's development, different regions of the fault zone alternate between periods of locking and slipping, which we can identify as interseismic, coseismic or aseismic (creeping) phases. Slipping patches can be delimited in order to define seismic events, of which we can measure the rupture surface, the amount of slip and the moment magnitude, and whose geometry can be visualized in 3D. The frequency-magnitude distribution of these events reproduces the well-known Gutenberg-Richter law.
This model is therefore capable of capturing multiple timescales, from short-term events (earthquakes), through seismic cycle, to the long-term evolution of seismicity. As such, is provides novel insights into the past, present and future dynamics of strike-slip faults.
Orateur: Adélaïde Allemand (IPGP) -
41
Slip rates and deep lithospheric deformation along a fault ruptured during the 2012 Mw 8.6 Wharton Basin earthquake
The traditional understanding of plate tectonics posits rigid plates primarily undergoing deformation at narrow plate boundaries. However, the equatorial Indian Ocean presents a unique scenario with a diffused deformation zone spanning ~3000 km within the Indo-Australian plate. Past investigations have identified N-S compression in the Central Indian Ocean basin and strike-slip motion along N-S trending reactivated fracture zones of a fossil spreading center in the Wharton Basin located at the eastern margin of the Indian Ocean. The massive Mw 8.6 earthquake on April 11, 2012, challenged the existing notions about the intraplate deformation in the Wharton Basin. Seismological and geodetic observations showed that in addition to the deep centroid depth and high-stress drop, the earthquake ruptured along a complex set of faults at high angles to the presumed north-south direction of slip motion along fracture zones, indicating the existence of additional fault systems. However, since the earthquake ruptured in the deep ocean, far away from land stations, the constraints on the fault characteristics (e.g., length, dip, strike, etc.) and rupture propagation remained poor. Recent studies in the Wharton basin mapped different classes of active faults and shear zones, compatible with the regional stress field and closely aligned with the fault plane solutions from the seismological studies. In this study, we analyzed high-resolution bathymetry, active source seismic, and sub-bottom profiler data to investigate the surface and subsurface expression of one of the faults that ruptured with a magnitude (Mw) of 8.3 during the earthquake. Bathymetry data revealed a complex fault geometry with en echelon segmentation and diffused deformation in some regions up to a total fault length of ~200 km. We found substantial evidence of both long-term deformation (since ~4-5 Ma) as well as recent deformation (since ~50 Kyr), preserved in transtensional type pull-apart basins with faults penetrating down to the basement and horizontal offsets in several bathymetric markers (such as seamount and submarine channels) due to strike-slip motion along this fault. We found seismic evidence of deep faults that penetrate down to the upper mantle compatible with the deep centroid depth (~30 km) of the earthquake. We suggest that the rupture along this fault played a significant role in transferring stress toward the epicentre of the Mw 8.2 aftershock that occurred 2 hours later after the Mw 8.6 event. We estimated the long-term horizontal and vertical slip rate along the fault to be varying between 0.1-0.7 mm/yr. Such slow slip rates could indicate a long recurrence time for large earthquakes along this fault. The results of this study will be crucial to understand the seismic hazard associated with large oceanic intraplate earth-quakes as well as the kinematics of the diffused deformation in the Wharton basin.
Orateur: Saksham Rohilla (IPGP)
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38
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15:00
Break
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Posters: Posters 2/2
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Shaping the Earth: Faults, Quakes, and Erosion: CDD-03 2/2
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42
Interactions between fault geometry, crustal damage and slip before, during and after the 2023 Kahramanmaraş earthquakes (Turkey)
Large continental strike-slip earthquakes usually present a complex rupture trace composed of several segments separated by discontinuities. Fault geometry may interact with stress concentration and rupture propagation and have an influence on the distribution of coseismic slip and the termination of ruptures. However, other factors can influence slip distribution and rupture propagation, such as the rheology of the fault and the bulk, which can be affected by crustal damage from earthquakes, and the initial stress state, which notably depends on slip history. Here we characterize these complex interactions in the case of the 2023 Mw 7.8 Pazarcık and Mw 7.5 Elbistan earthquakes that ruptured several segments of the East Anatolian Fault Zone (EAFZ) in south-central Turkey. We use a Bayesian framework to model coseismic slip in a layered elastic medium with geodetic data. In our model, most of the slip occurs above 15 km depth, with a shallow slip deficit. Shallow slip decreases at geometrical complexities supposedly due to off-fault deformation in these highly damaged areas. The termination of both ruptures also correspond to geometrical complexities. Aftershocks spread in wide fan-shaped damage zones around the southwestern tip of both ruptures, whereas they are more focused on the main fault or on subparallel planar structures to the northeast. We also build 2-year postseismic Sentinel-1 InSAR displacement time series and find that the segments with relatively strong shallow afterslip are located at the northeastern end of the rupture trace for both earthquakes. Preseismic InSAR time series computed by the FLATSIM service also show shallow creep on the Pütürge segment northeast of the Pazarcık rupture and more distributed deformation in the rest of the EAFZ. These observations suggest that deformation in the EAFZ is more localized to the northeast and more distributed to the southwest before, during and after the 2023 earthquakes. Our postseismic displacement time series also shows shallow creep on several secondary faults. Comparing these deformations to the stress changes caused by the 2023 earthquakes can give interesting rheological insights and help refine our understanding of the complex interactions between fault geometry, crustal damage and slip.
Orateur: Paul Dérand (ENS) -
43
An enhanced earthquake catalog of the 2010 Mw 8.8 Maule aftershock sequence using modern tools
Understanding rupture mechanisms, seismicity propagation, distribution, and migration after a major earthquake relies on the quality of earthquake catalogs, particularly their detection capabilities, location accuracy, and magnitude completeness. On February 27, 2010, a Mw 8.8 earthquake struck the Maule region in south-central Chile, causing widespread damage and substantial loss of life. As the largest well-instrumentally recorded earthquake in Chile, this event offers a unique opportunity to revisit an old dataset, refine the aftershock sequence analysis, and gain deeper insights into subduction zone dynamics.
Here we analyze ~10 months of continuous seismic data from the International Maule Aftershock Deployment (IMAD), a temporary network with about 156 stations deployed throughout the rupture zone. Using the recent Back-Projection and Matched Filtering (BPMF) workflow, which integrates PhaseNet, a deep-learning-based phase picker, we detected more than 100,000 earthquakes with at least 10 P and S-wave arrival phases. We relocated these events using NonLinLoc-SSST-Coherence, a probabilistic algorithm. A subset of them served as templates for template matching, producing a final catalog of about 375,000 events. This represents nearly a ninefold increase in detected events compared to prior catalogs and achieves a magnitude of completeness of Mw ~1.7, lowering it by over one order of magnitude.
Our catalog significantly enhances the spatio-temporal resolution, revealing intricate seismic structures (e.g., fault geometries) and dynamic post-seismic activity. Our improved relocations draw these key features, including the shallower seismic zone in the Pichilemu-Vichuquén region (33.5°S–35°S) and deeper seismic clusters near Concepción (37°S–38°S) in unprecedented detail. Temporal b-value variations (0.8–1.1) reveal zones of high-stress accumulation and the activation of multiple fault systems, highlighting the heterogeneous nature of post-seismic deformation. This high-resolution dataset underscores the potential of modern methodologies and algorithms, unveiling features from older data with improved clarity and detail.
Orateur: Rodrigo Flores Allende (IPGP) -
44
Characterisation of the soil properties along railway tracks using Distributed Acoustic Sensing
A precise understanding of the soil profile is important for railway operations, impacting not only vibration and noise propagation but also broader aspects such as train speed adjustments and infrastructure resilience. Soil properties influence track stability, and changes due to climate variations—such as extreme rainfall or drought—can affect safety and performance. Monitoring these variations enables proactive maintenance and operational decisions, including speed regulation to prevent track deformation or instability. Traditional geophysical campaigns using methods like geophones, while useful, are not suited for large-scale, long-distance monitoring. These methods provide valuable data but are limited by their spatial and time coverage, as they are temporary.
In this context, Distributed Acoustic Sensing (DAS) technology provides a complementary solution, enabling high-resolution, continuous monitoring over long distances. DAS uses optical fibers, installed for communication purposes along railway tracks, and we use the dark fiber to measure vibration. This study explores the potential of DAS for passive seismic monitoring of soil properties along railway tracks.
DAS operates by sending a laser pulse through optical fibers, where backscattered light is analyzed to detect strain-rate. SNCF has developed an in-house DAS for use in railway applications, allowing real-time monitoring of the tracks. DAS offers spatial resolution on the order of a meter, making it a valuable tool for large-scale monitoring and a complement to traditional geophysical site studies.
In this study, DAS is used for passive seismic monitoring of soil properties. The wavefields generated by passing trains are analyzed using cross-correlation and using a Multi-channel Analysis of Surface Waves (MASW) technique to analyze their propagation. These wavefield can also be used to characterize the dominant frequency of the site. This methodology could also enable the monitoring of soil conditions in earthworks, such as embankments, by detecting potential changes in soil properties. This provides valuable insights for early warning systems and improved maintenance strategies.
This work demonstrates how DAS technology can complement traditional geophysical methods for large-scale soil characterization along railway tracks. DAS is a promising, cost-effective tool for monitoring the tracks and the mechanical properties of the soil beneath, with no need for specialized teams to be deployed in the field.Orateur: Joseph Grand (IPGP) -
45
Spatial assessment of erosive processes in a badland catchment using diachronic LiDAR, Draix, Alpes de Haute-Provence, France
Badlands have been extensively studied for their erosion dynamics and sediment transport due to their remarkable sensitivity to climate forcing [1]. These erosion processes, primarily driven by mass wasting, are typically investigated at the plot scale using rainfall experiments [2] or at the catchment scale by integrating export measurements at gauging stations [1]. However, detailed spatial analysis of sediment dynamics within a catchment remains scarce [3]. This lack of spatially explicit data limits our ability to identify the contributions of various mass-wasting processes to the overall sediment budget and landscape dynamics.
This work is based on the Draix-Bléone observatory [4], which provides time series of suspended and deposited sediment loads for the Laval catchment (French Alps). This small (86ha), steep, denuded (up to 57%) and unmanaged catchment is instrumented at its outlet since 1983. These chronicles emphasize very high denudation rates (>300 T/ha/year) associated to strong seasonal storms [1]. In addition, we analysed a 6-year diachronic LiDAR scans that cover the whole catchment and conducted shallow-water modeling of its hydraulic network with the GraphFloods algorithm [5]. This allow us to assess the contributions of the different erosion processes to the geomorphological dynamics as well as sediment residence.
Our results highlight several compartments of the critical zone that contribute significantly to the total sediment budget. In particular, landslides and crests failures account for 15% of the export measured at the outlet, although these areas together cover only about 1ha. This corresponds to the extreme erodibility we measure in marls on submetric and metric specific drainage areas. We also identify important sediment sinks that regulate export, such as the narrowing of the main channel upstream of a slow-moving landslide. In addition, uncleared debris on slopes and in elementary gullies represent in average 30% of the mass balance of associated slides, underscoring their central role in sediment dynamics.
Our results highlight the complex interplay between sediment sources and sinks in shaping steep badland catchments. By combining high-resolution spatial analysis with long-term monitoring data and hydraulic modeling, this study provides new insights into how small-scale processes drive large-scale sediment budgets. It contributes to wider efforts to model sediment flows in sensitive and rapidly changing landscapes.[1] N. Mathys et al., (2003). Erosion quantification in the small marly experimental catchments of Draix (Alpes de Haute Provence, France). Calibration of the ETC rainfall-runoff-erosion model. CATENA. DOI:10.1016/S0341-8162(02)00122-4. [2] D.J. Oostwoud Wijdenes and P. Ergenzinger (1998). Erosion and sediment transport on steep marly hillslopes, Draix, Haute-Provence, France: an experimental field study. CATENA. DOI:10.1016/S0341-8162(98)00076-9. [3] J. Bechet et al., (2016). Detection of seasonal cycles of erosion processes in a black marl gully from a time series of high-resolution digital elevation models (DEMs), Earth Surface Dynamics. DOI:10.5194/esurf-4-781-2016. [4] S. Klotz et al., (2023). A high-frequency, long-term data set of hydrology and sediment yield: the alpine badland catchments of Draix-Bléone Observatory. DOI:10.5194/essd-15-4371-2023 [5] B. Gailleton et al., (2024). GraphFlood 1.0: an efficient algorithm to approximate 2D hydrodynamics for Landscape Evolution Models, EGUsphere, DOI:10.5194/egusphere-2024-1239.
Orateur: Yassine Boukhari (Institut de Physique du Globe de Paris)
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42
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09:30
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10:00
Breakfast
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Flows of Change: Climate, Water, and Surface Processes: CDD-04
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46
On the forces at play during kilometer-scale iceberg calving: insight from numerical simulations
Iceberg calving is a complex process often followed by the capsize of the newborn iceberg because of the torque created by the buoyancy and gravity forces. In the case of kilometer-scale icebergs, calving/capsize events can trigger seismic waves (glacial earthquakes) recorded hundreds of kilometers away by global seismic networks. These recordings contain information on the seismic source such as the calved-iceberg volume as well as the contact force applied by the iceberg on the glacier, the glacier dynamical response but also water waves and flow following the capsize.
To obtain an accurate estimation of the iceberg volume, it is necessary to couple seismic inversion of glacial earthquakes with numerical modeling of the capsize [Sergeant 2019]. Therefore, based on our previous work, we use a Computational Fluid Dynamics (CFD) model to simulate the fluid-structure interaction between the ocean and an iceberg capsizing against a glacier terminus. The model reproduces with great accuracy lab experiments (rotation kinematics, effect of calving type, hydrodynamic pressure, etc).
In this talk, we will focus on field-scale simulations. We will show that the forces applied on the glacier terminus due to the hydrodynamic pressure and to the iceberg-glacier contact appear to have similar magnitude, are of opposite signs, and depend on the iceberg geometry. We also give a first estimation of the glacier deformation under the action of these forces.
https://doi.org/10.5194/egusphere-egu25-6688
Sergeant, A. et al. (2019) ‘Monitoring Greenland ice sheet buoyancy-driven calving discharge using glacial earthquakes’, Annals of Glaciology, 60(79), pp. 75–95. doi:10.1017/aog.2019.7.
Orateur: Nicolas DE PINHO DIAS (IPGP/ECN) -
47
Growth of a drainage network in the lab
In most environments, rainfall infiltrates into the porous ground, and forms a body of groundwater which flows into the neighbouring river network. The groundwater discharge is particularly strong near river heads where it triggers seepage erosion, causing existing channels to grow headward. Occasionally, this process initiates the development of new river branches, leading to the formation of a ramified network. Because seepage erosion is slow, drainage networks take hundreds to thousands of years to build. Therefore, observing their evolution in the field is difficult if not impossible. To bypass this issue, we build a laboratory experiment that allows us to replicate the formation of a drainage network over a few days. The experimental set-up consists of a square box of side 1.5 meter and height 30 cm. We fill the box with a 10 cm layer of cohesionless plastic grains (size 0.8 mm). The layer of grains forms an erodible aquifer. We inject water into the aquifer from below, at a rate controlled by a water tower. Groundwater homogeneously fills the aquifer, and flows towards the outlet of the set-up, positioned along one side of the box. If the discharge is large enough, the flow erodes the aquifer, and entrains sediments out of the system. This process initiates the growth of a drainage network. With time and increasing discharge, the network grows until it covers the entire experiment. Using a simple 2D model to solve the Poisson equation, we compute the shape of the groundwater table as the network changes. The numerical solution, validated by piezometric measurements, reveals the interplay between channel head growth and groundwater flow. Our laboratory experiment thus demonstrates that seepage erosion alone is sufficient to generate a branching network, offering a unique opportunity to observe the formation and evolution of river networks within a confined drainage area.
Orateur: Céleste Romon -
48
Reweaving the river’s story: A data-driven approach to stream chemistry prediction and interpretation
Rivers act as the primary harmonizer of the critical zone, integrating processes that regulate nutrient cycling, water quality, and energy flow within ecosystems. A deeper understanding of the hydro-biogeochemical processes warrants the study of river chemistry at a detailed temporal resolution, but this is often hindered by logistical challenges associated with traditional sampling and data acquisition.
Recent advances such as the RiverLab “lab-in-the-field” setup now allow sub-hourly monitoring of major ions and physico-chemical parameters, enabling novel insights that were previously eclipsed by coarse sampling. This facilitates inquiries into transient processes e.g. storm events, and aids the modelling and evolution of sources contributing to stream chemistry.
Despite these advancements, challenges remain. Issues such as sensor malfunctions, power outages create data gaps that impede the application of statistical methods, bias the model outputs and obscure patterns of periodicity. Collectively, these pose a risk of misconstruing
water quality trends that can negatively influence policy decisions.This talk outlines an approach combining Singular Spectrum Analysis and machine learning to “reconstruct” the stream chemistry, countering the aforementioned issues and laying the foundation for a low-cost monitoring-forecasting framework. Additionally, we will also touch upon the application of Dynamic Factor Models (DFMs), as a new tool for source
apportionment from hydro-geochemical time series data.Orateur: Amita Prajna Mallik (Institut de Physique du Globe de Paris, CNRS, Université Paris Cité, Paris (75005)) -
49
A dive into seasonal forecasting of groundwater resources: from hydrometeorological modelling to data assimilation.
In France, groundwater is one of the main resource for industry, agriculture, and drinking water.
As severe droughts affecting groundwater become more frequent,
the development of forecast has become essential for stakeholders.
The hydro-meteorological platform Aqui-FR (Vergnes et al., 2020), which gather
different groundwater models, is coupled with atmospheric reanalysis and downscaled seasonal forecasts
(Willemet et al., 2022) to achieve this goal.
However, due to the lack of observations of subsurface parameters, uncertainties in such models can remain high.
This often leads to bias (difference between observations and simulations) or poor representation of process dynamics.
Such errors degrade the estimation of the state variable used to initialise the forecast and
propagate errors in the forecast itself.To overcome these issues, a data assimilation (DA) scheme, based on the Ensemble Kalman Filter (EnKF ; Evensen et al. (1994))
has been developed within the Aqui-FR workflow.
By using measured observations in combination with a dynamical system model, derives an optimal estimate of the system states, together with an uncertainty estimate.
Here, the analysis focuses on hydrological state variable estimation, and more specifically on piezometric (groundwater) levels.
In situ piezometric data from monitored wells are assimilated into a hydrological model,
that uses the hydrogeological computer code MARTHE (Thiéry, 2020) to simulate both piezometric levels
and river discharge, at regional basin scale.First results obtained from numerical experiments show the benefit of DA on groundwater state estimation
with a regional model (mean RMSE reduced from 4.26 to 0.32), even with spatially sparse data. When assimilation is
stopped, the analysis shows an impact on state estimation up to a seasonal time step (mean RMSE about 2.9 after 180
days without assimilation), which is encouraging for forecast improvements. However, in regions of the model domain where
initial calibration is too poor, the correction shows less persistence and the dynamics of the model appears to be driven
by parameters rather than initial conditions. To improve the piezometric estimation in these areas, we plan to implement a two
step DA with parameter estimation before state estimation.Evensen, G. 1994. "Sequential Data Assimilation with a Nonlinear Quasi-Geostrophic Model Using Monte Carlo Methods to Forecast Error Statistics". Journal of Geophysical Research: Oceans 99(C5):1014362. doi: 10.1029/94JC00572.
Thiery, D. 2020. Guidelines for MARTHE v7.8 computer code for hydro-systems modelling. BRGM/RP-69660-FR. Orléans, France: BRGM.
Vergnes, JP, N. Roux, F. Habets, P. Ackerer, N. Amraoui, F. Besson, Y. Caballero, Q. Courtois, JR de Dreuzy, P. Etchevers, N. Gallois, DJ Leroux, L. Longuevergne, P. Le Moigne, T. Morel, S. Munier, F. Regimbeau, D. Thiery, and P. Viennot. 2020. "The AquiFR Hydrometeorological Modelling Platform as a Tool for Improving Groundwater Resource Monitoring over France: Evaluation over a 60-Year Period". HESS 24(2):633-54. doi: 10.5194/hess-24-633-2020.
Willemet, J-M., S. Munier, F. Besson, P. Etchevers, P. Le Moigne, F. Rousset, J.-M. Soubeyroux, Ch. Viel, F. Habets, Ph. Ackerer, N. Amraoui, J.-R. de Dreuzy, N. Gallois, C. Magand, D. Thiéry, and J.-P. Vergnes. 2022. "Aqui-FR: Towards a Hydro-Geological Seasonal Forecasting System for Metropolitan France". in Vol. IAHS2022-525. Montpellier, France: Copernicus Meetings.Orateur: Adrien Manlay (BRGM) -
50
Statistical analysis of geogenic CO2 dispersion in lower atmospheric layers using an integrated approach: Application to the Syabru-Bensi Hydrothermal System, Central Nepal
Highly concentrated geogenic CO2 emissions have been reported worldwide. Although atmospheric dispersion is most common, specific topographic and meteorological conditions can lead to surface accumulation in the form of “CO2 rivers”. While catastrophic events, - such as the deadly limnic eruption of Lake Nyos in 1986, are well documented, the behavior of these CO2 rivers remains poorly understood, posing challenges for risk assessment and mitigation. Although computational models such as CFD and integral models provide analytical insights, their practical application in risk management is hampered by computational cost and accuracy constraints. To address these limitations, we simulate the behavior of CO2 rivers by using the depth-averaged numerical model TWODEE which provides a computationally efficient alternative for simulating dense flows. TWODEE is based on shallow-layer continuity equations, where negative buoyancy drives the cloud dynamics, causing it to settle into a low-lying configuration. External physical forces are included in the form of three empirically parameterized terms: turbulence induced by terrain roughness, turbulence associated with atmospheric convection, and shear stress at the atmosphere-flow interface. To improve predictive capabilities, we rely on an integrated approach that compares simulation results with experimental results from analog laboratory experiments and field data collected at CO2 degassing sites. In analog experiments, high-density salt water is injected turbulently into a tank of lower-density fresh water and onto a rough and sloped surface. The volume flow rate, the slope angle and the surface roughness vary between each experiment. The recorded images allow the measurement of frontal and extensional velocities, which are then used to calibrate the model parameters. The model is tested at the Syabru-Bensi Hydrothermal System (SBHS) in central Nepal, where high seismicity and significant CO2 degassing have been reported. In the field, at each measurement point, the airborne CO2 concentration and the wind velocity and direction are measured at 0, 50, 150, and 300 cm above the ground, and the surface CO2 flux is measured using the accumulation chamber method. Our results suggest a refined set of model parameters that are consistent with previous studies. In addition, we assess the impact of the 2015 Mw 7.9 Gorkha earthquake, which triggered both the emergence of additional CO2 degassing vents and changes in CO2 flux across the SBHS. This work aims to improve our understanding of the dispersion of dense gases in the lower atmospheric layers. By quantifying the budget of CO2 rivers in different geodynamic contexts and estimating health risks in both volcanic and non-volcanic environments, this work lays the foundation for an operational hazard assessment tool with potential applications in real-time risk management.
Orateur: Marie Margot Robert (Institut de Physique du Globe de Paris)
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46
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12:00
Lunch
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Probing the Deep Earth: Volcanoes, Primitive Earth and Planetary Cores: CDD-05
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51
Keynote 06: From magma oceans to solid mantles: experimental insights into the differentiation of terrestrial planets
Planetary magma oceans were ubiquitous on terrestrial planets in the early Solar System and enabled their differentiation into a silicate mantle and an iron-rich core (metal-silicate differentiation). Over time, these large-scale magma oceans progressively solidified due to secular cooling, and their crystallization led to the formation of the main petrological and geochemical reservoirs in the mantle (magmatic differentiation). These two differentiation processes—metal-silicate and magmatic—are major planetary events that set the initial conditions of planetary bodies, and it is therefore essential to better constrain them.
To this end, the development of high-pressure experimental tools (such as large-volume presses and diamond anvil cells) since the mid-20th century has been a major advancement. On one hand, metal-silicate partitioning experiments conducted under core-formation conditions are used to infer the composition of planetary cores. On the other hand, crystallization experiments under conditions representative of the terrestrial mantle have helped us better constrain the solidification of Earth's magma ocean.Orateur: Héloïse Gendre (IPGP) -
52
Evolution of carbon dioxide dynamics in alkaline volcanic lake Dziani Dzahav
From May 2018 to the end of 2020, an underwater eruption gave birth to a new volcanic edifice, the Fani Maoré, 50 km east of Mayotte (Indian Ocean). Today, concerns on the volcanic activity in the area persist, and scientific community and authorities are on the lookout for signs of changes in volcanic activity.
Magmatic degassing can be observed on Petite-Terre Island of Mayotte archipelago as CO2 bubbling at the airport beach and in volcanic lake Dziani Dzaha. Since the eruption of Fani Maoré, an increase in degassing into the lake has been visually observed. This phenomenon likely attests of potential changes in the large-scale magmatic activity. We aim to quantify the degassing in the lake for a better characterization of these changes and identify future strategies for monitoring.
We present here geochemical measurements (water column chemistry, CO2 diffusive fluxes) from 2011 to 2024, covering the period before, during and after the eruption. Prior to 2020, the carbon cycle in the lake was well established and relatively stable. Between 2020 and 2022, pH of the lake went from 9.2 to 8 and CO2 diffusive fluxes at the water-air interface increased 20-fold. Most of the geochemical parameters in the lake are stable since June 2022.
Consistently with the observations of increased degassing, our findings suggest that the lake is continuously supplied by large amounts of magmatic CO2. Its pH is now controlled by [CO2]aq that itself reflects the balance between CO2 supplied to the lake and CO2 lost by diffusion at air-water interface. This allows us to estimate the quantity of CO2 dissolving in the lake as roughly 35 tons d-1. Additionally, modelling outputs suggest that the lake is highly sensitive to changes in input fluxes, and that pH and pCO2 are key parameters to follow for the monitoring of magmatic CO2 fluxes in Dziani Dzaha.
Orateur: Jonas Frère (Institut de Physique du Globe de Paris, Paris, France) -
53
Seismic Evidence of Hydrated/dehydrated Lava Flows at the Layer 2A/2B boundary from Full Waveform Inversion of Ultra-long Offset Multi-channel Seismic Data at the Axial Volcano in the Pacific Ocean
The magmatic upper crust is generally divided into Layer 2A and Layer 2B, where Layer 2A is interpreted to consist of lava flows and Layer 2B of dikes, although hydrothermal alteration processes have also been suggested to define the Layer 2A/2B boundary. Using 3D seismic reflection method at the Axial Volcano in the Eastern Pacific, we have recently imaged > 3 km of layered lava flows that dip inwards towards the rift zone and interact with the axial melt lens, hence indicating the absence of a dike sequence. These images also show the injection of melt sills within the lava pile. However, the conventional stacking of wide-angle data (triplication associated with the high velocity gradient zone at the base of Layer 2A) indicates that a classical Layer 2A/2B boundary can be defined in our study area. Here, we present results of seismic full waveform inversion applied to ultra-long offset (12 km) multi-channel seismic data collected in 2019 during the same survey that yielded the 3D seismic reflection results. In our high-resolution P-wave velocity section and associated velocity gradient section we find layered structures consistent with the 3D seismic image. We also find (1) a low-velocity layer in the upper part, evocative of Layer 2A, (2) a high-velocity gradient zone underlain by (3) a high-velocity but low-gradient zone (similar to Layer 2B) underneath, all within the imaged thick lava pile. We suggest that the uppermost lava flow layer consists of hydrated lava flows whereas the lower layer has undergone dehydration and metamorphism and has been formed by the interaction of lava flows with melt bodies and injected sills. Thus the classical Layer 2A/2B boundary would correspond to the boundary between hydrated and dehydrated lava flows. Our results suggest that the upper oceanic crust is formed by lava flows and their interactions with melt-sills, which resolves the long-standing debate about Layer 2A/2B boundary.
Orateur: Wenxin XIE (IPGP) -
54
Hydrating the oceanic lithosphere: from transforms to trench
Oceanic Transform Faults (OTFs) are active, strike-slip plate margins, which offset the mid oceanic ridges and form the Ridge Transform Intersections (RTI) on either ends. Beyond the active part, OTF’s fossil record is preserved as Oceanic Fracture Zone (OFZ), which eventually subducts at the convergent margins and often exhibits higher hydration/alteration and distinct mechanical properties from the surrounding oceanic lithosphere (e.g., clustered seismicity at shallow and deep levels, higher production of earthquakes and weaker seismic coupling at the OFZ-subduction interface). Such different OFZ-architecture is observed through δ11B enrichment in arc lavas produced above the subducted OFZ. However, processes responsible for such geochemical and geophysical characteristics of OFZ, and their long-term effect in subduction dynamics remain enigmatic. These processes are thought to be operational at the active part of the OFZs, e.g., at OTFs, where low seismic velocity anomaly and high Vp/Vs ratios are observed. Recent petrological studies of ultramafic rocks from transform faults suggest deep deformation-driven fluid percolation, which acts as effective weakening mechanism and is responsible for intense lithospheric hydration. However, the deformation and fluid-rock interactions affecting the magmatic crust at the transform faults remain elusive.
In this study, we investigate amphibolites and foliated-metagabbros collected from the east-RTI and Southern Transverse Ridge (STR) of the Vema Transform Fault at Mid-Atlantic Ridge. Micro-structural and geochemical analyses show four possible deformation regimes affecting the magmatic crust: (1) A high-temperature magmatic regime (~900–950 °C), marked by plastic deformation and melt-rock interactions, resulting in formation of brown amphibole, ilmenite-magnetite-apatite, and associated secondary plagioclase & clinopyroxene. (2) A high-temperature hydrothermal regime (~750 °C) associated with semi-brittle deformation and fluid-rock interactions at amphibolite facies, evidenced by presence of syn-deformational green-amphibole, secondary plagioclase, sphene-ilmenite and chloro-apatite. (3) Subsequent medium-temperature (~500 °C) phase with dominantly brittle deformation and fluid-rock interactions at greenschist facies, linked to hydrothermal fluid infiltration, producing green-amphibole, chlorite, and sphene; finally, (4) A low-temperature (~200 °C) brecciation phase with zeolites forming in the breccia-matrix. These distinct deformations and fluid-rock interactions show variable hydration/alteration, leading to chemical and rheological modifications of the magmatic crust at the Vema OTF. Understanding and quantifying the amount of fluid percolation and its depth as well as spatial distribution of the modified magmatic crust is essential to infer the dynamics of subduction zones linked to hydrated lithosphere along convergent margins.
To explore the effect of hydrated OFZ lithosphere at subduction, we conducted thermomechanical modeling, with and without incorporating the OFZ in the oceanic lithosphere. Our experiments show that the mobility of fluids play a crucial role in deforming the mantle wedge: i.e., when fluid migration is efficient, dehydration and subsequent fluid release from subducting OFZ-incorporated lithosphere, starts at shallow depth and continues over broader depth range. This produces distinct deformation regions and sustained hydration in the mantle wedge, also affecting long-term forearc hydration and deformation. By integrating petrological studies with numerical modeling, this work shows how the inherited P–T–fluid-deformation histories of oceanic transform-lithosphere may affect long-term subduction zone dynamics, fluid-flux, and the volatile cycles.Orateur: Sampriti Mukherjee (IPGP) -
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Semi-convective planetary cores
The recent Juno and Cassini space missions delivered a wealth of observations of Jupiter and Saturn.
Constraints from gravity data and ring seismology suggest that these planets host a dilute core of substantial size, in which the concentration of heavy material increases with depth.
This stabilising compositional gradient coexists with a destabilising thermal gradient induced by the secular cooling of these planets.
As thermal anomalies diffuse on time scales much shorter than compositional anomalies, this configuration is prone to fluid instabilities termed semi-convective instabilities.
Semi-convection has been studied in the context of oceanography and astrophysics.
Results from local models in Cartesian geometry show that semi-convection can take the form of internal gravity waves or layered convection, in which sharp interfaces separate well-mixed regions that can eventually merge.
In order to check to which extent these results can be applied to the interior of giant planets, we have conducted a parametric study of semi-convective dynamics in a non-rotating, non-magnetised sphere, using the MagIC code.A linear stability analysis shows that the instability takes the form of internal gravity modes, whose morphology and eigenfrequency can be adequately explained by an analytical solution derived in the ideal (diffusion-free) limit.
In particular, we find that the onset mode corresponds to the fundamental mode of the diffusion-free problem.Past the onset, we identify three distinct regimes of semi-convection from our catalogue of 93 simulations.
In the first regime, close to onset, internal gravity modes emerge, with a large-scale azimuthal structure near the centre of sphere, and finer-scale structure near the surface (Fig.1a).
The fluid remains stably stratified, and the transport of composition and temperature across the domain is weak.
Triadic interactions between small-scale, unstable gravity modes and large-scale, stable gravity modes explain the overall stability of this regime.The second regime is reached upon further increase of the thermal driving: internal gravity modes initially emerge but a convective core eventually develops at the centre (Fig.1b).
This core grows with time and finally occupies the whole fluid volume, which makes the transport of composition and heat more efficient than in the first regime.
Lastly, for the most driven simulations, convective layering occurs (Fig.~1c). In this third regime, the number of layer increases with the level of thermal driving.
These layers have a finite lifetime and they ultimately merge to yield a state of global overturning convection.We discuss the application of our findings to the interior of Jupiter, that could operate either in the second or third regime, based on a tentative extrapolation of our results.
Orateur: Sonja Zhou Wahlgren (IPGP)
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Conclusion
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15:00
Hekla Party
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