Spatial Variations of Deformation along a Strike-Slip Fault: A Case Study of Xianshuihie Fault Zone, Southwest China  
[PERSON]  
Key Laboratory of Shale Gas and Geoengineering, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China; [EMAIL_ADDRESS] (J.L. ); [EMAIL_ADDRESS] (S.Q. ); [EMAIL_ADDRESS] (Q.W. ); [EMAIL_ADDRESS] (B.Z. ); [EMAIL_ADDRESS] (Y.Z. ); [EMAIL_ADDRESS] (X.L.) School of Civil Engineering, Chang'an University, Xi'an 710061, China; [EMAIL_ADDRESS] (J.L.) Innovation Academy of Earth Science, Chinese Academy of Sciences, Beijing 100029, China (J.L. of damage zones based on geologic maps, field surveys, and microstructural analyses of orientated rock samples [2; 17], as well as the characterization of the damage zone evolution associated with geologic faults, based on numerical models and diagenetic environments [11; 18; 19]. In general, determining the width of the fault damage zone is crucial. It is usually defined by the distribution and frequency of the cracks, fractures, and deformation zones of the damaged structures, which normally decreases with increasing distance from the main fault core [20]. For quantitatively portraying the width of fault damage zones, some scholars carried out studies on the scalar correlations between the width and displacement of fault damage zones based on fault evolution models [21], while others studied the distribution pattern of the damage zones based on the statistical evaluation of the fracture frequency at a distance from the fault zone [22; 23]. There often exists a close correlation between the width of the damage zones and the cumulative displacement of the fault, but it is still relatively difficult to accurately quantify the extent of width of the damage zones associated with an active fault because the physical and mechanical characteristics of the rock in the damage zones change progressively away from the core of the main fault [24; 25]. Most of the studies regarding the determination of the width of the fault damage zones targeted small-scale faults [4; 23], and knowledge of the rock damage conditions surrounding large-scale active fault zones is still absent, especially when they have a length of more than 100 km. However, large-scale fault zones, which usually act as boundary faults between lithospheric plates, have a significant impact on the control of the regional crustal stress-deformation field and profoundly influence seismic activities [26; 27]. The development of the damage zones around such large geologic faults is closely related to the regional geomorphic evolution and mountain hazards [28; 29] in that area. Since the 21 st century, many major strategic projects have been proposed in southwest China; therefore, for safe and resilient construction of these projects, prior determination of the width of the damage zones along major faults is a crucial activity. For this study, we selected the Xianshuihie fault zone (XSHF) in the eastern margin of the Qinghai-Tibet Plateau (Figure 1a) [30]. In the Cenozoic, the Tibetan Plateau uplifted and its materials moved and extruded eastward. As a result, the Mesozoic structures in the western margin of the Yangtze block were superimposed and transformed into large-scale strike-slip faults and thrusts [31; 32], and the XSHF is one of the most active faults and serves as the eastern boundary of the Qinghai-Tibet Plateau; it also has unique intracontiental deformation characteristics [33]. The XSHF is a prominent arclinear, northwestern-southeastern trending fault. In the vicinity of the Huiyuan temple basin, the XSHF can be divided into northwestern and southeastern segments. The northwestern segment of the XSHF is characterized by a left echelon pattern, while in the southeastern section, four secondary sub-faults diverged through the Huiyuan temple basin and eventually developed southward in Kangding, where XSHF splays coincided.