安宁河断裂带南段滑动速率估计

DETERMINATION OF SLIP RATE ON THE SOUTHERN SEGMENT OF THE ANNINGHE FAULT

安宁河断裂作为青藏高原地区川滇地块东边界断裂系的重要组成部分,研究其断层活动性,特别是晚第四纪以来断层滑动速率,能够为进一步揭示川滇地块的变形机制和运动学特征提供一定的基础资料。目前安宁河断层的滑动速率研究主要集中在断裂的北段,而南段相关的研究还比较少。文中选择在安宁河断裂南段的大水沟和帽盒山2个地点,通过高精度影像解译、实地测量、探槽开挖及14C年代测试,获得大水沟一带近3 300a以来断层左旋平均位移速率约4. 4mm/a,推测帽盒山地点的断层左旋位移速率可能为2. 6～5. 2mm/a。2个地点的位移速率存在较好的一致性,该位移速率与安宁河断层北段基本一致,另外考虑到南北2段的古地震复发周期相近的特征,认为安宁河断层南北2段的断层活动性存在一致性。

The Anninghe Fault has been suggested as an important segment of the fault system along the eastern boundary of the Sichuan-Yunnan faulted block in the southeastern region of the Tibetan plateau.Reliable determination of the Late Quaternary slip rate on the Anninghe Fault is very helpful and significant for revealing deformation mechanism and kinematic characteristics of the Sichuan-Yunnan faulted block,which further helps us understand fault activity and seismic potential of the region.However,previous studies were focused mainly on the northern segment of the Anninghe Fault,while slip rate on its southern segment has been less studied.Therefore,in this paper,we chose two sites at Dashuigou and Maoheshan on the southern segment of the Anninghe Fault,and used high-resolution images of unmanned aerial vehicle(UAV)photogrammetry technology,detailed field survey,multiple paleoseismic trenching and radiocarbon dating methods to constrain slip rate on the southern fault segment of the Anninghe Fault.Specifically,we suggest that the slip rate at the Dashuigouo site is narrowly constrained to be^4.4mm/a since about 3￣￣300a￣￣BP based on a linear regression calculation method,and speculate that a slip rate of 2.6~5.2mm/a at the Maoheshan site would be highly possible,although we poorly constrained the whole deformation amount of the two branch faults at the Maoheshan site from multiple paleoseismic trenching.The data at the two sites on the southern segment show a consistent slip rate compared with that of the northern segment of the Anninghe Fault.Moreover,considering a similar paleoseismic recurrence interval on the two segments of the Anninghe Fault from previous studies,we further suggest that the fault activity and deformation pattern on the two segments of the Annignhe Fault appears to be well consistent,which is also in agreement with the regional tectonic deformation.