Abstract: In this paper, the eikonal equation-based seismic tomography method was used to invert the velocity structure of the source and surrounding area of the Changning M_S6.0 earthquake in 2019. High-resolution 3-D P- and S-wave velocity as well as the P-wave azimuthal anisotropy models are obtained, and Poisson's ratio of several typical profiles is analyzed. The results show that the azimuthal anisotropy significantly affects the P-wave travel times, revealing strong crustal heterogeneities in the study area. Some low-velocity anomalies have good spatial correspondence with industrial activities fields, which may indicate the properties of upper crustal media have been affected by the shale gas hydraulic fracturing, fluid injection in salt minefields, and/or disposal of wastewater in natural gas fields. The Changning M_S6.0 earthquake may be directly induced by salt mining by water injection, and the velocity anomaly structure caused by industrial activities may have a sustained effect on the occurrence of earthquakes in the region. The P-wave azimuthal anisotropy in this region may be dominated by the plate motion and principal compressive stress. The anisotropy in the shallow depth of the Changning earthquake source region shows near EW direction, which is consistent with the direction of regional principal compressive stress. These results provide new insight into the fine crustal structure, deep material movement, and dynamic mechanism in the southeastern margin of the Sichuan Basin.

Key words: The 2019 M_S6.0 Changning earthquake, Seismic tomography, 3-D velocity models, P-wave azimuthal anisotropy