The Possibly Inducing Mechanism of the 2019 Changning Earthquake Sequence: New Evidence from Geodetic Observations

Abstract The mechanism that induced the 2019 Changning earthquake sequence is still a subject of debate. The discussion focuses on the dip angle of the seismogenic fault, which is directly associated with the intersection of the fault and the salt well of the Changning salt mine. This study employs Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System data to analyze the co- and postseismic deformation caused by the 2019 Changning earthquake sequence. The coseismic slip distribution model is constrained by geodetic observations, along with the geometry of the seismogenic faults. The afterslip model is also inverted from InSAR time series approximately one year following the mainshock. The findings indicate that the Mw 5.7 mainshock of the 2019 Changning earthquake sequence ruptured an approximately east–west-trending fault in the Changning anticline, with a dip angle of ∼53°. InSAR observations identified the displacement field resulting from the Mw 5.3 aftershock on 22 June. The majority of the coseismic ruptures took place in regions at depths less than 5 km. The afterslip was primarily observed at depths of 2–4 km, with a peak slip of 0.16 m. The aseismic slip exhibited significant overlap with the coseismic rupture, while minimal seismic and aseismic slip was detected in proximity to the salt wells of the Changning salt mine. According to the geodetic data and previous seismological findings, we propose that the seismogenic fault of the Changning earthquake did not have a direct intersection with the salt wells. Contrasting with the previous established “directly intersected” mechanism, this study introduces a “indirectly intersected” model for the Changning earthquake. This potentially induced mechanism can explain most of the seismological and geodetic observations.