Late Quaternary activity of the Songgang Fault on the eastern Tibetan Plateau from geological and geomorphological evidence

Abstract

The Late Quaternary activity characteristics of faults are essential for understanding regional strain distribution and estimating seismic hazards. The Bayan Har block, located in the northern Tibetan Plateau, is a region with a high level of seismic hazard. Remarkably, over the past three decades, many strong earthquakes have occurred on the block boundary fault zones of the Bayan Har block. However, the 2021 Ms 7.4 Maduo earthquake and the 2022 Maerkang Ms 6.0 earthquake swarm were exceptions as they took place within the Bayan Har block, not on the boundary fault zones. The reason for the occurrence of these intraplate earthquakes presents an interesting research query. The Songgang Fault (SGF) is a NW-trending strike-slip fault within the Bayan Har block. The 2022 Maerkang Ms 6.0 earthquake swarm occurred 6 km northeast of the SGF. What role did the SGF play in the process of the earthquake swarm? Through utilizing high-resolution remote sensing image interpretation, detailed field geological and geomorphologic surveys, trench analysis, and dating technologies, we found that the SGF is a sinistral strike-slip active fault since the Late Pleistocene, exhibiting tectonic behavior conducive to the preparation and occurrence of moderately large earthquakes. OSL dating of dislocated stream channels reveals a left-lateral slip rate of the SGF yields 1.6–2.1 mm/yr since the Late Pleistocene. The SGF distributes and transmits the tectonic deformation within the Bayan Har block, accommodating southeastward lateral extrusion of the Bayan Har block materials and contributing to the kinematic mechanisms of the entire eastern margin of the Tibetan Plateau. Furthermore, the 2022 Ms 6.0 Maerkang earthquake swarm exhibits a conjugate rupture phenomenon in a complex tectonic zone where several secondary fault planes of the SGF converge. This main fault zone deserves attention as a potential source zone of future earthquakes.