Unmanned Aerial Vehicle Aeromagnetic Analyses Reveal the Causative Faults and Seismogenic Mechanism of the 2021 Ms 6.0 Luxian, China, Earthquake

Abstract

Abstract On 16 September 2021, an Ms 6.0 earthquake occurred in Luxian, Sichuan, China, breaking the historical record of no earthquake with magnitude ≥ M 6 along the Huaying Mountain fault belt. The regional geological structure is primarily controlled by the northeast-striking fault belt, but the long axis of the isoseismic line, distribution of early aftershocks and coseismic rupture plane all strike northwest, posing challenges to the seismogenic mechanism. To investigate this, we conducted a 400  km2 unmanned aerial vehicle (UAV) aeromagnetic survey near the epicenter, with a line spacing of 1 km. Through aeromagnetic analyses, combined with the spatial distribution of relocated foreshocks and aftershocks, we outline potential basement causative faults and a change in the structural trend between the shallow and deep portions of the seismic zone. We conjecture that the Luxian earthquake was triggered by the hydrofracturing-driven reactivation of a pre-existing northwest-striking and southwest-dipping basement fault, of which the upward propagation induced extrusion and dislocation at the hypocenter within the sedimentary layer. The special structural configurations for the focal area could contribute to the stress concentration and occurrence of large earthquakes.