Seismic activity characteristics of the Tongkuang Shan fault (Southeastern Tian Shan, China) revealed by high-resolution topographic data

Abstract

With the rapid development of remote sensing technology, it is getting easier to obtain high-resolution topographic data, which is of great significance for quantitative investigations of active tectonics, particularly in inaccessible regions. The Tongkuang Shan Fault is a thrust fault located within the Yanqi Basin in the southeastern Tian Shan Mountain, and can be divided into the west and east segment based on the fault geometry. Although obvious fault scarps have developed along the fault, its activity has rarely been investigated since most part of the fault is located in a closed military area. In this study, the Worldview satellite stereoscopic images were utilized to create a 0.5 m resolution Digital Elevation Model (DEM) and orthoimage of the Tongkuang Shan Fault. Based on the high-resolution topographic data, we interpreted the geometric structure of the fault, classified the different geomorphic units, and measured the vertical displacements along the fault. A total of 296 vertical displacements were measured on different geomorphic surfaces along the fault trace. The results show six distinct clusters in the distribution of vertical displacements along the fault, with peak values at 1.4 ± 0.4/1.5 ± 0.5 m, 3.0 ± 0.7/3.4 ± 0.6 m, 5.7 ± 0.9/5.5 ± 0.7 m, 8.9 ± 1.2/8.2 ± 1.3 m, 15.4 ± 1.0/16.2 ± 0.9 m, and 28.3 ± 1.8/26.5 ± 1.5 m on the west and east segment, respectively, which are in good agreement with the vertical displacements acquired from different geomorphic units, indicating a multiple phase of activity on the fault. The fault may have undergone at least six strong paleoseismic events, and the smallest displacement cluster (1.4 ± 0.4/1.5 ± 0.5 m) is considered to be the coseismic displacement of the most recent event, yielding an earthquake magnitude of approximately M_w 7.0–7.2. Moreover, the coefficient of variation of the first four peak displacements are 0.39 and 0.24 for the two segments, indicating a high repeatability of paleoseismic displacements on the fault, potentially conforming to a characteristic earthquake model.