云南中甸-大具断裂马家村-大具段古地震初步研究

中甸-大具断裂马家村-大具段位于哈巴雪山北麓及玉龙雪山以北的大具盆地内,总体走向310°～320°,根据卫星影像解译和详细的野外地质地貌调查,认为中甸-大具断裂马家村-大具段自第四纪以来长期活动,横跨断裂的水系右旋位错量可分为8.5～12m、22m左右、47m左右、200～280m、500～510m和1000m左右6个等级。在大具盆地内发现了长约600m的地震地表破裂带,这是该断层段在全新世活动的直接地质证据,在破裂带南东端附近开挖的探槽揭示出自晚更新世以来断裂存在三期活动,可能对应3次地震事件,结合前人在该断裂段获得的地质剖面和断错地貌面测年结果,分析认为马家村-大具段自晚更新世以来至少发生了3次古地震事件,发生时间分别为4910～45 a BP、7000 a BP左右和32.93～19.96ka BP,利用垂直同震位移值估算了水平同震位移量,最终得出每次地震事件的震级为7.5级左右。

A Preliminary Study of Paleo-earthquake in the Majiacun-Daju Section of Zhongdian-Daju Fault,Yunnan Province

Majiacun-Daju segment of Zhongdian-Daju fault is located in the north piedmont of Haba Snow Mountain and the Daju Basin of the north of Yulong Snow Mountain with an overall strike of 310°~320°. The satellite image interpretation and detailed field geological and geomorphological survey suggested that Majiacun-Daju segment of Zhongdian-Daju fault has been active for a long period since Quaternary,and the dextral displacements of the rivers across the fault were divided into six grades of 8.5~12m,about 22m,about 47m,200~280m,500~510m and about 1000m. An earthquake surface rupture zone with a length of about 600m was discovered in the Daju Basin,which is the direct geological evidence of Holocene activity of the fault section. The trench excavated near the southeastern end of the rupture zone revealed that there existed three active times along the fault since late Pleistocene,which may correspond to three earthquake events. Based on the geological profile and fault geomorphological surface dating obtained by the previous people in the fault section,we believed that there exist at least three paleoseismic events in Majiacun-Daju segment of Zhongdian-Daju fault since the late Pleistocene,which occurred in 4910~45aBP,about 7000aBP and 32.93~19.96kaBP respectively. The horizontal coseismic displacement is estimated by using the vertical coseismic displacement value,and the magnitude of each event is about 7.5.