Coseismic Rupture Behaviors of the January and March 2022 MW > 5.5 Hala Lake Earthquakes, NE Tibet, Constrained by InSAR Observations

On 23 January and 25 March 2022, two M-W > 5.5 Hala Lake earthquakes characterized by right-lateral strike-slip faulting occurred around the Elashan Fault in Northeastern Tibet, marking the two largest events since the 1927 M-W 6.2 Hala Lake earthquake. Since no surface rupture related to the two earthquakes has been reported, the seismogenic faults and coseismic rupture behaviors of the two events are still unknown. The occurrence of the two events provides a rare opportunity to gain insight into the seismogenic structure and rupture behavior of the less studied region, further helping us accurately evaluate the regional seismic hazard. Here, we first exploit Interferometric synthetic aperture radar (InSAR) data to obtain the coseismic deformation associated with the two earthquakes and then invert for the fault geometry and detailed coseismic slip of the two events. Coseismic modeling reveals that the January and March 2022 earthquakes ruptured two buried west-dipping moderate-angle and high-angle right-lateral strike-slip faults, respectively. Most of the slip of the January event occurred at depths from 1.7-7.6 km, while the majority of the slip associated with the March event occurred at depths from 2.5-10 km, which may have been restricted by the intersections between the January and March Hala Lake seismogenic faults. By a comprehensive analysis of the coseismic inversions, stress changes, and early postseismic signal, we suggest that the significant fault dip difference (similar to 30 degrees), highlighting a fault segmentation, stops the rupture propagation from one fault segment to another and that fluid migration may encourage the restart of the rupture of the later event, which requires further investigation. Moreover, Coulomb stress modeling shows stress loading on the eastern segment of the Daxueshan-Shule Fault and the northern segment of the Elashan fault, which we should pay more attention to.

Automated summary

On January 23 and March 25, 2022, two right-lateral strike-slip earthquakes with magnitudes larger than 5.5 occurred near Hala Lake in northeastern Tibet. These two events are the largest since the 1927 Hala Lake earthquake. The lack of surface rupture makes it difficult to determine the seismogenic faults and coseismic rupture behaviors of the two events. However, studying these events can provide valuable insights into the seismic hazard of the region.