Rupture Directivity of the 2019 M-w 5.8 Changning, Sichuan, China, Earthquake and Implication for Induced Seismicity

摘要

On 17 June 2019, an ML 6.0 earthquake struck the Changning county in Sichuan Province of China, causing substantial casualties and property losses. The earthquake is the largest and the most damaging event in the Changning area and close to shale gas and salt mining production region. To investigate the possibility of the earthquake being induced, we resolve its rupture dimension and hypocentral depth via modeling of local seismic waveforms. The result reveals that its hypocentral depth is about 4 km, much shallower than most tectonic earthquake in surrounding regions. From moment tensor inversion (nodal plane 1 [NP1], strike 125 degrees/dip 46 degrees/rake 28 degrees; NP2, strike 14 degrees/dip 70 degrees/rake 132 degrees), the earthquake is found to be a strike-slip event with significant thrust component. We resolved rupture directivity via measuring the difference between centroid location and hypocenter location, and found that the causative fault is NP1 and ruptured northwestward with length about 14 km. Based on its shallow hypocentral depth, and proximity to nearby mining regions, we hypothesize that the Changning earthquake might be an induced event due to long-term fluid injection for salt mining. However, interdisciplinary studies are needed to test the hypothesis, including simulation of fluid migration and investigation of background stress as well as resolving mechanical parameters of the rocks in the epicentral regions.