Complex seismogenic fault system for the 2022 Ms6.0 Maerkang (China) earthquake sequence resolved with reliable seismic source parameters

Abstract

The Bayan Har block in central Tibetan Plateau is characterized by low historical seismicity and has rarely experienced M6+ earthquakes. However, on June 10, 2022, at 01:28 AM (UTC + 8), an $M_s$6.0 earthquake struck Maerkang in Sichuan Province, China, within the Bayan Har block. Four foreshocks and eight aftershocks with magnitudes greater than 3 occurred during the week of the mainshock with the largest foreshock reaching $M_s$5.8. Previous studies have suggested two probable seismogenic faults. One proposes that the earthquake sequence occurred on the V-shaped Songgang secondary fault, while the other suggests an unmapped fault located east of the V-shaped fault is the causative fault. Additionally, there are inconsistencies in the focal depth and rupture direction in these studies. To better identify the seismogenic faults of the Maerkang earthquakes, we first estimated the focal mechanisms and centroid depths of all M$\ge$2.9 events during one week of the mainshock occurence, using both regional and teleseismic waveform data. We then refined the mainshock epicenter by by incorporating 3D velocity models to account for their influence on the earthquake location. Other events were relocated relative to the mainshock using the surface wave differential times. Finally, we analyzed the rupture directivity of the mainshock and the $M_s$5.8 foreshock via the empirical Green's function (EGF) method. The results suggest that the mainshock likely ruptured along an unmapped fault to the east of the V-shaped Songgang secondary fault, while the $M_s$5.8 foreshock occurred on the Songgang fault itself, suggesting complex fault system for the earthquake sequence.