Primary Surface Ruptures of the LudianMw 6.2 Earthquake, Southeastern Tibetan Plateau, China

Abstract

Online Material: Google Earth images. A M w 6.2 earthquake struck Ludian County at 08:30:11 UTC (16:30:10.2 local time) on 3 August 2014 and is one of the most destructive earthquakes that has occurred on an unmapped active fault east of the Xianshuihe–Xiaojiang fault system between the Chuandian rhomb block (the Sichuan–Yunnan block), southeastern Tibetan plateau, and the South China block, a stable tectonic terrain (Fig. 1; Wen et al. , 2013; X. Xu, Jiang, et al. , 2014; Cheng et al. , 2015). Its hypocenter is located at 27.11° N, 103.35° E, at a depth of ∼12 km, adjacent to Longtoushan Township, ∼29 km southwest of Zhaotong City (Liu et al. , 2014; L. Xu et al. , 2014; Y. Zhang et al. , 2014). The relocation of the aftershocks and a little of the reported fieldwork results may demonstrate the seismogenic fault of the Ludian earthquake is the Baogunao–Xiaohe fault, a northwest-trending left-lateral strike-slip fault, which cut through the Zhaotong–Lianfeng fault zone (http://www.eq-igl.ac.cn/contents/41/867.html, last accessed August 2014; Fang et al. , 2014; Liu et al. , 2014; W. Wang, et al. , 2014; X. Xu, Cheng, et al. , 2014; X. Xu, Jiang, et al. , 2014). We know nothing at all about the former, whereas the latter is a highly developed northeast-trending reverse fault with a right-slip component (Wen et al. , 2013). The finite-source inversion using regional seismic broadband data suggests the hypocenter of the Ludian earthquake was initiated from ∼12 km in the upper crust, then propagated unilaterally to the southeast and upward to the shallow with a peak left slip of ∼0.7 m; it likely offset the ground to form a surface rupture zone 10 km in length (Liu et al. , 2014), but there is no any reliable evidence to support or oppose this view. The significant directivity of the rupture propagation during …