新生逆冲断裂地表垂直位错分布与断层活动性关系:以河西走廊临泽断裂为例

Vertical Slip Distribution along Immature Active Thrust and Its Implications for Fault Evolution: A Case Study from Linze Thrust, Hexi Corridor

活动断裂地表位错定量研究对理解断裂活动习性和构建多周期地震复发模型有重要意义.前人基于高精度地形数据对断裂地表位错分布开展了大量定量研究,但是关于累积位错变形沿新生逆冲断层的走向分布特征依然不清楚.本文选择河西走廊内部新生临泽逆冲断裂(<20 ka)为例,利用UAV(unmanned aerial vehicle)航测方法采集了断裂沿线约8 km长、2.5 km宽的高精度(0.5 m)地形数据,开展了精细地貌填图(1∶500)、断层垂直位错测量(73个)、断层活动定量参数分析以及野外地质调查等工作.研究揭示,新生临泽逆冲断裂主要由2条左阶展布分支逆冲断层组成(L1和L2),阶区宽度约260 m.位错测量揭示,断层最大和最小累积位错分别为4.5 m和0.2 m,累积垂直位错呈明显不对称三角形分布,断层上位移亏损点与断层几何形态变化区域明显对应.断裂位错定量参数分析显示,临泽断裂结构不成熟,两个分支断裂后期会在破裂长度和位错增加下逐渐贯通.因此,可能需要注意后期强震活动造成新生逆冲断层向盆地内部拓展,及其对邻近城镇带来的直接和衍生灾害效应.

Slip distribution is necessary for the understanding and construction of rupture behavior along active faults. Although large number of researches have been focused on this issue using high-resolution topographic data, the slip distribution along immature active thrusts is still unclear. Two significantly different scenarios exist on this issue until this day. One is the large variation triangular distribution, and the other is comparatively uniform distribution. Using 8 km length, 2.5 km width and 0.5 m resolution UAV derived DEM data;we mapped in detail the geomorphic units, measured 73 vertical separations, and analyzed the parameters of the surface rupture. The Linze thrust is mainly composed of two left stepping branches, and the width of the step is~260 m. The triangular slip distribution, with maximum and minimum vertical throws of 4.5 m and 0.2 m, respectively, reveals progressively lateral propagation of the thrust. The analysis of surface rupture parameters for the Linze thrust reveals the immature structure and the trend of connection and propagation of the segmented branches. Thus, more attention possibly should be paid to the influence of the propagation and connection of the thrust for the neighboring counties.