- © 2015 by the Seismological Society of America
Online Material:Tables of focal mechanisms and crustal models.
On 3 August 2014, an Ms 6.5 earthquake struck Ludian County, Zhaotong City in Yunnan Province, China (hereafter called the Ludian earthquake). Although this earthquake was not very big, it caused unusually severe damage (Cheng et al., 2015; Li et al., 2015). Thus, studying the causes of the severe damage from this moderately strong earthquake may help us evaluate seismic hazards of similar earthquakes. There are many kinds of factors that may play important roles in the damage caused by the Ludian earthquake, including site effects, quality of buildings, a large difference between surface-wave magnitude and centroid magnitude, and so on. Besides these effects, other factors, especially the characteristics of the source properties, such as focal depth and seismogenic environment, may be also important reasons for such serious damages.
The relocation of the aftershock sequence (Wang et al., 2014) (Fig. 1) suggests that the Ludian earthquake may be occurred at the east side of the Xiaojiang fault, which is surrounded by a series of active faults, including the Lianfeng fault and the Zhaotong–Ludian fault (ZLF). In addition, there is a secondary fault called the Baogunao–Xiaohe fault (BXF), which is a conjugate fault of the ZLF (Xu et al., 2003). Under compression from the northward-moving Tibetan plateau and with the presence of the strike slip of the active faults in the Sichuan–Yunnan region (Royden et al., 2008), the seismicity in the source region of the Ludian earthquake and its surrounding areas is quite high. Several moderate earthquakes occurred in this region in recent years (Fig. 1; Lv et al., 2013; Wen et al., 2013). Many aftershocks occurred after the Ludian earthquake. By UTC time 23:00 on 23 August, there had been 1573 aftershocks with magnitude greater than 1.0, …