High resolution catalog of the Luxian (Sichuan, China) MS6.0 earthquake sequence and analysis of the seismogenic structures

Abstract

The epicenter of the Luxian M_S6.0 earthquake on September 16, 2021, was located in the southern Sichuan Basin, which is a historically seismically quiescent area. In recent years, the frequency of earthquakes has increased with the large-scale exploitation of shale gas. No evident surface fractures or seismic faults were observed after the Luxian earthquake. Based on high-quality data recorded by a dense seismic array composed of 70 portable stations with an average spacing of 2–3 km, a high-resolution seismic catalog was constructed for 7 days before and 36 days after the M_S6.0 earthquake using LOC-FLOW, an effective workflow of phase picking, phase association, and earthquake location. Based on the new earthquake catalog, four earthquake clusters that occurred within the Yujiasi Syncline during this period were identified. Among them, the M_S6.0 main earthquake sequence had a NW-SE trend and inclined towards the SW, with a length of approximately 8 km and width of 5 km. The M_S6.0 earthquake sequence only appeared after the mainshock. The other three clusters were located in the northeast direction of the M_S6.0 earthquake sequence, all of which were NE-SW trending strips and had no evident direct correlation with the M_S6.0 mainshock. The focal depth was concentrated in the range of 2–7 km. Based on the seismic sequence profile and structural background, the M_S6.0 seismic structure may be a blind buried fault zone with a NW strike composed of multiple small conjugate faults with NE and SW dip. The fault was not exposed on the surface and was related to the detachment structure in the deep part of the Sichuan Basin.