3D Crustal Structure and Seismicity Characteristics of Changning–Xingwen Area in the Southwestern Sichuan Basin, China

Abstract

Using seismic data recorded on permanent and temporary stations around the Changning area in the Sichuan basin, the high-resolution 3D crustal VP, VS, VP/VS models and earthquake locations in the Changning–Xingwen area are obtained using the VP/VS model consistency-constrained double-difference seismic tomography method. The results show that crustal structures in the source area of the 2019 Ms 6.0 Changning earthquake have significant variations, especially in the depth of 0–7 km. Seismic activity in the Shuanghe and Yutan anticline areas before the Ms 6.0 Changning earthquake outlined several northeast-trending stripes, implying pre-existing small-scale faults that are perpendicular to the major northwest-striking faults in the Changning–Shuanghe anticline system. We found that the Ms 6.0 Changning earthquake broke through these pre-existing small-scale faults and extended from the Shuanghe to the Yutan anticlines. Both the rupture process and aftershock activity were influenced by the pre-existing small-scale faults. Most earthquakes within the Changning area are located in a slant zone that gradually deepens from the Shuanghe anticline on the east to the Yutan anticline on the west with the maximum depth from 5 to 10 km, which are associated with obvious high-VS and low-VP/VS features. The relocated seismic clusters in the Luochang–Jianwu syncline area have different strikes and dips, which are mainly located at the edge of low-velocity anomaly bodies and correspond to the low-VP/VS area.

Upper crustal velocity and seismogenic environment of the <em>M</em>7.0 Jiuzhaigou earthquake region in Sichuan, China

“…This observation indicates that the high‐speed area is prone to rupture, which is also the reason that the aftershock sequence in the southern part of the earthquake area is deeply distributed. The distribution characteristics of the aftershock sequence of the M 6.0 Changning earthquake in 2019 also reinforce this point (Zuo KZ et al, 2020). Therefore, we can conclude that the spatial distribution of the Jiuzhaigou earthquake sequence is closely related to the velocity structure of the medium around the earthquake area.…”

Numerical simulation of the stress field and fault sealing of complex fault combinations in Changning area, Southern Sichuan Basin, China

“…The faults in the northeastern part of the study area have long extents and large fault throws, while small faults are mainly developed in the south and west; the main fault strikes are NE and NNW, which are quite different from the fold strike. 10,51,52 The faults in the region are superimposed under the influence of tectonic stresses with multiple stages and directions; this situation has led to multistage and multiform fault and fold combinations, which have great importance for the enrichment of shale gas and improvements in reservoir performance and productivity (Figure 1).…”

Enhanced 3D velocity structure, seismicity relocation and basement characterization of Changning shale gas and salt mining regions in southern Sichuan basin

“…This continuous flow of data has led to several seismic studies within the region, many of which focused on seismicity location and focal mechanism determination. A couple of researchers have recently utilized varying portions of this data flow to determine velocity models at these scales (Long et al, 2020;Zhang et al, 2020;Zuo et al, 2020). Pioneering seismic tomographic study of the region is that of Long et al (2020), which used 5,252 events recorded on relatively sparse seismic stations and 1-D initial velocity model developed from large-scale tomographic results of Zhao and Zhang (1987).…”

“…Given that the region has undergone extensive fluid injection involving over 200 wells (Figure 1B) since 2014, it is imperative that the V s model should reflect features related to fluid distribution. Recently, Zuo et al (2020) used a more complete version of the regional data set made up of 24,640 earthquakes, recorded by an array of 86 seismic stations to determine the crustal velocity structure of the region up to 5 km by 5 km resolution in the longitude and latitude directions. Their results show obvious high V s and low V p /V s ratio features for seismicity within the region, suggesting no fluid influence on seismicity.…”