Abstract: On December 18, an M_S6.2 earthquake occurred in Jishishan County, Gansu Province, which causing casualties and property losses. The earthquake occurred on the northeastern margin of the Qinghai-Tibet Plateau where developed two groups of typical fault structures due to the extension of the Qinghai-Tibet Plateau to the northeast. The NWW trending large left-lateral strike-slip faults are seemed as the boundaries of the active blocks, and the other group of NNW-trending right-lateral strike-slip faults develop within the blocks as the secondary block boundaries. The Jiashishan M_S6.2 earthquake occurred in the large compression stepover between the NWW-trending left-lateral strike-slip fault zone of the north margin West Qinling and the NNW-trending Riyueshan right-lateral strike-slip fault zone, and the seismogenic tectonic is determined to be the southeastern segment of Lajishan fault zone named eastern margin of Jishishan fault. The distribution of aftershocks are strictly limited to the south of Yellow River and within the Dahejia tertiary basin in the eastern piedmont of Jishishan. The ridgelines and piedmont lines on the eastern section of Lajishan and Jishishan are discontinuous, and there are fault triangle faces along east bank of Yellow River which flows between the two mountains. It is speculated that a transverse fault with the function of adjusting the regional differential compression deformation is developed in this area. This fault cuts the southeastern segment of Lajishan fault zone and may make the eastern margin of Jishishan fault to be an independent active segment with a length of less than 40 km. It is determined that the possibility of a larger earthquake occurring in this area is not high in near future.

Key words: The 2023 Jishishan M_S6.2 earthquake, Seismogenic tectonics, Northeastern margin of the Qinghai-Tibet, Lajishan fault zone