Comparison of induced seismicity in Changning and Gongxian-Junlian area

Abstract:

Since the 1980s, salt mining operations have been existing in Changning county, Sichuan Province, China, which have an indispensable impact on local seismic activities. M_S 6.0 Changning earthquake (Yi et al., 2019), the largest earthquake in Sichuan Basin on record, happened in this area on 17 June 2019, which could be related to the injection for salt mining. While the shale gas exploitation in the Gongxian-Junlian area, not far from Changning County, has begun since 2012, which made the frequency of small earthquakes in the region surge since 2015. Particularly after the M_S 4.9 earthquake occurred in Junlian County on 28 January 2017, a series of moderate earthquakes occurred in this area. Most of these earthquakes have the characteristics of shallow focal depth and strong sense, and some of them caused casualties. M_S 5.7 Xingwen earthquake, the largest earthquake in the local area, was suggested to be induced by shale gas hydraulic fracturing operation (Lei et al., 2019).

Due to the different tectonic environment and injected volume in each exploitation area, the characteristics of induced seismicity could be relatively different, which provides a basis for studying the correlation of induced earthquakes. In this study, double-difference tomography (tomoDD) method (Zhang and Thurber, 2003) was employed to carry out the relocated results and high-resolution three-dimensional velocity structure of Changning and Gongxian-Junlian area. Combined with regional geologic data and injection data, characteristics of the seismic activity of two areas are compared and discussed respectively. All these results could provide an important basis for understanding the seismogenic environment and reasonably evaluation of the regional potential seismic risk in the two study area.