安宁河断裂西支全新世活动证据

Holocene Activity Evidence of West Branch of Anninghe Fault in Southeastern Tibet

安宁河断裂是川滇菱形块体东边界主要构成断裂之一,在冕宁县城附近因南河断裂与其汇交,导致该区域断层几何结构复杂。通过地质考察和探槽开挖,新发现了一段全新世活动断裂,命名为安宁河断裂西支。通过典型断错地貌位移测量和年代学样品测试得到调查点左旋滑动速率为(1.6±0.2)mm/a。开挖的古地震探槽揭示了2次古地震事件,分别为(2300±30)~(1700±30)a BP之间的一次地震和公元1536年7½级地震。已有研究在安宁河断裂南段获得的2次大地震事件与本次探槽揭示的地震事件时间较好地对应,说明安宁河断裂南段的大震事件可能导致了安宁河断裂西支同时破裂。

Anninghe fault controls eastern boundary of Sichuan-Yunnan rhomboid block,and its structure is complex near Mianning County.Based on geological investigation and excavation,the fault is Holocene fault in chronology.Combined with offset geomorphology and chronology,the left-lateral slip rate of the fault is 1.8 mm/a.The excavation indicates that the West branch of the Anninghe fault has occurred two Paleoearthquakes since 2130 a BP at least,whose active ages are(2300±30)~(1700±30)a BP and 1536 a,respectively.The west branch of the Anninghe fault does not have a large scale enough to trigger large earthquake.Two major seismic events in the southern segment of the Anninghe fault caused the simultaneous rupture of the western branch of the fault.