Description
Large earthquakes commonly occur along plate boundaries, but, although less frequent, they can also take place within slowly deforming continental interiors. In these intraplate settings, deformation is challenging to measure with geodetic methods, and the long recurrence time of major earthquakes means that direct observations — instrumental or historical — are scarce. Aftershocks and persistent microseismicity along the faults responsible for these major ruptures therefore provide key information for understanding the behaviour of intraplate fault systems whose seismic potential remains poorly constrained.
The 1905 Tsetserleg–Bulnay earthquake sequence in Mongolia — the largest recorded intraplate rupture sequence, with two magnitude-8 events — provides a unique natural laboratory to explore the dynamics of large intraplate fault systems. More than a century later, this fault system still produces a surprisingly high rate of small earthquakes. To investigate this ongoing activity, CEA (France) and IAG (Mongolia) deployed a dense temporary seismic network at the junction of the main ruptures. Using modern automated processing workflows, we detected and precisely located thousands of micro-earthquakes, revealing the fine-scale architecture of the fault system at depth.
Our observations reveal a highly uneven pattern of microseismicity: some fault segments are highly productive while others are almost quiet. This spatial variability, together with fault kinematics, highlights the role of the stress field orientation in controlling the current activity of the fault system. These observations help revisit how the 1905 earthquake sequence unfolded. Moreover, the depth distribution indicates that the fault system has not fully healed and may still be undergoing long-term post-seismic processes.
Beyond this regional case study, our results highlight the potential of temporary seismic experiments to better characterize fault structure and dynamics in intraplate regions where observations remain limited. This presentation will take the audience from field investigations in the Mongolian steppe to the interpretation of fault processes beneath the surface, offering a broader perspective on the behaviour of intraplate fault systems.
| Speaker information | PhD 2nd year |
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