川西理塘断裂晚第四纪活动性及古地震复发特征

Late Quaternary activity and paleoearthquake recurrence characteristics of the Litang fault in western Sichuan

块体内部活动断裂具备发生7级以上大地震的能力,其空间展布特征、活动性及地震危险性不容忽视。理塘断裂带位于川滇块体内部,是川西高原理塘地区重要的发震构造。关于理塘盆地地表破裂的形成时代、理塘断裂的古地震复发特征及运动性质仍存在争议。本文基于遥感解译、野外调查、无人机摄影测量、古地震探槽、^(14)C测年等手段,厘定了理塘断裂的空间几何展布、活动性及古地震历史。研究结果表明,理塘盆地地表破裂可能为1948年理塘M71/4级地震和1729年理塘地震叠加形成。理塘断裂古地震复发行为符合丛集地震特征,与毛垭坝断裂强震复发特征较为相似,指示两者可能同时发生破裂。理塘断裂运动性质为左旋走滑兼有正断分量,除受控于青藏高原东南缘侧向挤出运动,可能还受雅江和香格里拉次级块体差异运动的影响。本研究为理解川滇块体内部活动断裂的地震危险性、构造变形机制,以及区域重大工程规划建设与安全运营提供了详实资料。

Active faults within the block have the ability to trigger large earthquakes of magnitude 7 or above,and their spatial distribution characteristics,activity,and seismic risk cannot be ignored.The Litang fault zone is an important seismogenic structure in the Litang area of the western Sichuan plateau,which is distributed within the Sichuan-Yunnan block.There are still different understandings about the formation age of surface raptures in the Litang basin,the recurrence characteristics of paleoearthquakes,and the kinematic characteristics of the Litang fault.Based on remote sensing interpretation,field geological survey,unmanned aerial vehicle photogrammetry,paleoseismic trench exploration,and^(14)C dating,this paper has determined the spatial geometric distribution,activity,and paleoseismic history of the Litang fault.The research results indicate that the surface rapture of the Litang basin may be formed by the superposition of the 1948 Litang M71/4earthquake and the 1729 Litang earthquake.The recurrence behavior of paleoearthquakes along the Litang fault conforms to the characteristics of cluster earthquakes,which is relatively similar to the recurrence characteristics of strong earthquakes along the Maoyaba fault,indicating that both faults may rapture simultaneously.The movement of the Litang fault is characterized by sinistral strike-slip with normal fault components,which is controlled not only by lateral extrusion movements on the southeastern margin of the Tibet Plateau,but also by differential movements of the Yajiang and Shangri-La secondary blocks.This study provides detailed information for understanding the seismic risk and tectonic deformation mechanism of active faults within the Sichuan-Yunnan block,as well as for planning,construction,and safe operation of major regional projects.