念青唐古拉山东南麓断裂当雄段的全新世活动性与地震危险性分析

Holocene Activity and Seismic Hazard Analysis in Damxung of the Southeastern Piedmont Fault of Nyainqentanglha Mountain

根据遥感解译结果和野外实地考察,厘定出念青唐古拉山东南麓断裂当雄段有三条次级断裂在台地前缘平行展布,其切割台地前缘I级阶地并形成断层陡坎。通过测定错断地质体位移和收集沉积物年龄数据,认为该段全新世4ka以来,垂直活动速率约为1. 7 mm/a,左旋走滑活动速率约为0. 6 mm/a。综合分析认为,当雄盆地北缘所积累应变能在1952年谷露7. 5级地震和1411年羊八井8. 0级地震中未能够得到充分释放,据此推断该区应为念青唐古拉山东南麓断裂带上的地震空区,且全新世以来仍在持续积累应变能。该地震空区的断裂长度可视为潜在地震地表破裂的最小长度,利用Wells等模型计算认为,当雄盆地北缘断裂上潜在地震的最大矩震级至少为M6. 8级。

Based on interpretation of remote sensing and geological field survey result, three secondary faults are distributed in parallel in Damxung of the southeastern piedmont fault of Nyainqentanglha mountain,which form landform profile across normal faults of graben due to cut platform margin of grade I terrace scarp formation.Through researching the displacements and the collected sediments dates, it is obtained that the horizontal slip rate is about 0.6 mm/a, and the vertical slip rate is about 1.7 mm/a since 4 ka.The northern margin of Damxung basin is a seismic gap,which continuously accumulated strain energy is not released in the M7.5 Damxung earthquake and the M8.0 Yangbajain earthquake. The fracture length of the seismic space can be regarded as the minimum length of potential surface rupture. According to Wells et al., the maximum moment magnitude of potential earthquakes is at least M6.8.in northern margin of Damxung basin.