Relocation of the 2021 MW 7.4 Maduo, Qinghai, China earthquake sequence and implications for seismogenic structure

Abstract

An MW 7.4 earthquake struck Maduo County, Qinghai, China on 22 May 2021. To better understand the seismogenic structure of this region, we collect local earthquake arrival time data at the MAD station in the China Earthquake Networks Center observational bulletins during 1 June to 20 September 2021, and manually pick P and S wave arrival times from high-quality seismograms recorded at 34 recently deployed MaduoArray portable seismic stations. Using these arrival times, we relocate the Maduo earthquake sequence using earthquake association, absolute location and relative location methods. Our results show that the 2021 Maduo earthquake sequence occurred along the Kunlun Mountain Pass-Jiangcuo fault zone in the NWW-SEE direction and the aftershocks are located on both sides of the mainshock, showing characteristics of bilateral rupture. Vertical cross-sections of the aftershock distribution illustrate a nearly vertical shape of the seismogenic fault that tilts toward the northeast and southwest in different sections, reflecting a complex geometry of the fault plane. There is a horsetail bifurcation phenomenon at the eastern end of the fault zone. A sparse area of aftershocks appears at about 30 km east of the mainshock epicenter, which may be associated with a uniform fault friction and sufficient release of rupture energy caused by super-shear rupture of the mainshock. Taking into account many geophysical results including seismic tomography and magnetotelluric soundings, we speculate that the occurrence of the Maduo earthquake could be affected by crustal fluids in the fault zone. The fluids may ascend from the lower crustal flow beneath northeastern Tibet.