Coseismic and postseismic deformation of the Changning earthquake constrained by geodetic data

Abstract:

On June 17, 2019, the Changning Ms6.0 earthquake occurred in the Sichuan Basin, breaking a thousands-yr-long seismic quiescence for there is no M>6 historical earthquake recorded in the surrounding area. The aftershock activity continued up to now, which attracted much attention. Most of the previous studies focused on obtaining the focal mechanism and explaining the potential relationship between the earthquake and salt well mining, but the scientific contribution of geodetic data in this case has not been publicly displayed yet. We use GPS data and Interferometric Synthetic Aperture Radar (InSAR) images from the ALOS-2 and Sentinel-1 satellites in 4 different viewing geometries to map the coseismic surface deformation caused by this earthquake. Then the coseismic deformation field has been used to investigate both the fault geometry and rupture slip distribution. The results show that Changning earthquake sequence mainly occurred in the east-west buried faults in Changning anticline system. The Mw5.7 mainshock is characterized by deep thrust (~5km) and shallow strike slip (~1-3km). The main slip is concentrated in the depth range of 1-4km, and the maximum slip is 0.42m, with a depth of 2.68km. Geodetic data also distinguish the aftershock of Mw5.3 occurred on June 22. The aftershock is dominated by thrust, with the maximum slip of 0.27m. The slip directions of the main earthquake and Mw5.3 aftershock correspond to the direction of regional stress field, which proves that the Changning earthquake should be attributed to regional stress accumulation, and the salt well mining activities may accelerate the process of stress release. Continuous GPS observations and time series of the Sentinel-1 images show that the postseismic deformation of the Changning earthquake is not significant (less than 1cm). The westward expansion of Changning earthquake swarm is more likely to be related to Coulomb stress disturbance caused by the main earthquake.