Fault geometries of two moderate earthquakes in the interior of Asia
Continent revealed by InSAR
Abstract
Intra-continental dip-slip earthquakes often occur in the orogen and
rift zones with complex tectonics, providing rare opportunities to
illuminate the deformation and evolution of continental structures.
However, due to the sparse seismological and geodetic observations, such
earthquakes are less studied. Here, we report the fault geometries of
two dip-slip earthquakes recently occurred in Southern Tian Shan and the
Mongolia-Baikal rift zone revealed by InSAR . The 2020 Mw6.0 Jiashi
earthquake occurred in the Keping-tage fold-and-thrust belt in southwest
Tian Shan. This region is seismically active, yet most well-recorded
earthquakes occurred south of the mountain front. The lack of large
earthquakes beneath the belt thus hinders our understanding of the
orogenic process to the north. Combining InSAR measurements and
relocated aftershocks, we found that a fault model involving a shallow
thrust fault and two deeper faults can best reconcile the surface
deformation and aftershock distribution. Stress analysis suggests that
slips on the shallow fault reactivated the older basement structures at
depth. Our results reflect the basement-involved shortening activated by
a thin-skinned thrust faulting event with surface deformation, implying
a southward orogenic process of the southwest Tian Shan. The 2021 Mw6.7
Lake Hövsgöl earthquake occurred in the Mongolia-Baikal rift zone
(MBRZ), which is located in the northern tip of the northern Mongolia,
and is bounded by the Tibet Plateau orogenic belt and the Siberian
Platform. Using the Bayesian inversion method we derived a fault plane
with two slip patches, one is mainly strike slip and the other is mainly
normal slip component. The correlation between the observed and
predicted displacements by the single fault model is 97.46%. Coulomb
stress analysis shows that the 2021 event has a triggering effect on the
western segment of the Tunka Fault to the north, where no large
earthquakes have occurred since the 1905 M8+ earthquake, raising the
potential for seismic risk in this region.