Coseismic surface deformation and source mechanism of the 2023 Ms 6.2 Jishishan earthquake, northeastern Tibetan Plateau

On 18 December 2023, the Ms 6.2 Jishishan earthquake struck the border region of Gansu province and Qinghai province in the northeastern Tibetan Plateau in China. Field investigations revealed that the 2023 Ms 6.2 Jishishan earthquake produced a ∼1.2-km-long coseismic surface deformation zone with the characteristic centimeter-sized uplift and bulge in the range of 1–13 cm (generally<5 cm), which was mainly restricted to a narrow corridor of 40–50 m in width along an previously-unknown frontal blind fault of the North Lajishan thrust fault zone. In spatial location, the coseismic surface deformation zone corresponds to the core of a late Cenozoic anticline on the hanging wall of blind fault, indicating that the coseismic surface uplift was constrained by the pre-existing tectonic environment.

The North Lajishan thrust fault zone is composed of the west branch fault (F1), east branch fault (F2) and the frontal blind fault (F3), the surveying results document that only the frontal thrust fault (F3) is the Holocene seismically active fault. Thus, the seismogenic fault of the 2023 Ms 6.2 Jishishan earthquake was suggested to be the F3 fault, indicating the northeastward propagation and expansion of the most recent earthquake activities within the North Lajishan thrust fault zone related to the ongoing northeastward shortening of the northeastern Tibetan Plateau accommodating the Eurasia-India continental collision.