Electrical resistivity structure of the Southeastern part of Bayan Har Block: Insights into the seismogenic environment of 2022 Maerkang earthquake swarm

Abstract

The Bayan Har block (BHB) is one of the areas with the strongest seismicity in China. Since 1997, six earthquakes with magnitudes of 7 or greater have occurred in this block. The activity of earthquakes has shown a trend of increasing from the edge of the BHB to its interior. In this article, three-dimensional inversion was used to generate the electrical resistivity structure in the Maerkang earthquake area based on magnetotelluric data in the Maerkang earthquake area in the southeast of the BHB. Combined with the electrical resistivity structure characteristics of the Maduo earthquake area in 2021 and the Jiuzhaigou earthquake area in 2017, the seismogenic environment and tectonic deformation in the BHB were revealed and analyzed. The electrical resistivity structure revealed that the Songgang fault was an electrical resistivity contrast zone that extends into the middle and lower crust, and connects to the Dari fault zone to the northwest, which is the seismogenic fault of the 2022 Maerkang earthquakes. The resistivity structure of the BHB exhibits a layered structure with a widespread high-conductivity layer in the middle and lower crust. The burial depth of the high-conductivity layer is undulating in waves along the profile, which may be a deep manifestation of the strong shortening deformation in the middle and lower crust of the region. The lower crust of the BHB is a medium with a high melt fraction, which may provide a material source for the flow of the middle and lower crust in the northeastern part of the Tibetan Plateau and may be an important controlling factor in the occurrence of moderate and strong earthquakes in the region.