The 2019 MW 5.7 Changning Earthquake, Sichuan Basin, China: A Shallow Doublet With Different Faulting Styles

Changning county in Sichuan Basin belongs to major salt‐producing resources, with water injection wells drilled to ~3‐km depths. Enhanced occurrence of small earthquakes was observed in the last ~10 years. However, on June 17, 2019, a damaging earthquake struck the region. Seismic agencies reported diverse focal mechanisms and pointed to departures from shear faulting, typical for tectonic events. To understand these enigmatic features, we modeled records from 12 broadband seismic stations, adding over 100 first‐motion polarities. We found that the earthquake was very shallow (~4 km) and consisted of two shear events: the initial thrust faulting and the following strike‐slip faulting along an SE‐NW trending near‐vertical plane, aligned with aftershocks. The initial episode was “normal,” expected on existing faults and supported by tectonic stresses of the region. Contrarily, the significant strike‐slip faulting appears to be rather “abnormal,” probably facilitated by the initial shock and by elevated pressure of underground fluids. The 2019 earthquake provided a rare opportunity to illuminate interplay between long‐lasting water injections, tectonic stress, complexity of existing faults, and their dynamic interactions. That is how seismology aims at making industrial activities sustainable and safe.