关键词: 青藏高原, 拉脊山断裂带, 2023年积石山M_S6.2地震, 发震构造, 地震地表破裂

Abstract: Surface rupture is an important feature of earthquake occurrence, and a valuable tool for studying earthquake dynamics and tectonic deformation. It is generally believed that surface ruptures are only formed by earthquakes with magnitudes of M6$\frac{3}{4}$ or greater. However, in recent years, surface ruptures have also been observed in earthquakes with magnitudes of M6.0 or less. This study aims to explore the methods for identifying surface ruptures in moderate earthquakes. The identification of the seismic structures of moderate earthquakes is challenging, mainly due to the following factors: ① the relatively small scale of surface ruptures in moderate earthquakes (such as displacement, width, length, and depth), making them easily covered by thick loess and hidden; ② non-tectonic fractures interfere with the identification of tectonic fractures. In this study, we conducted a preliminary analysis of the identification markers of the seismic structures of moderate earthquakes based on the Jishishan M_S6.2 earthquake. We proposed the following identification markers. ① geometric distribution and profile morphology of surface ruptures, linear distribution of secondary disasters (landslides, collapses, sand liquefaction, etc.) associated with earthquakes provides references and clues for identifying the seismic structure; ② the rupture runs stably across different geomorphic units along the rupture direction and at least crosses one low terrain such as a gully; ③ the rupture on the geological profile shows a stable dip; ④ tectonic morphology associated with surface ruptures that develops alternating echelons folds (compressional mounds) and tension cracks along the rupture. The identification markers proposed in this study provide new ideas for the identification of the seismic structures of moderate earthquakes.

Key words: Qinghai-Tibet Plateau, Lajishan fault zone, The 2023 Jishishan M_S6.2 earthquake, Seismic structure, Earthquake surface rupture