川南泸州地区地震重定位与地壳三维速度结构研究

近年来全球范围内页岩气水力压裂开采区地震活动剧增的现象，引起社会公众、政府、产业部门和科学家的广泛关注.利用2010年至2021年期间四川南部区域台网和流动台站记录的近震P波和S波到时数据，采用双差层析成像方法，对泸州及周边地区地震位置和地壳浅部介质结构进行了联合反演.重新定位后，中小地震震源深度主要处于2~10 km范围内.在空间上，地震活动呈现丛集特征，集中在螺观山背斜和古佛山背斜之间的低缓区内，并具有一定的时空迁移特征.背斜以南区域和泸县M6.0地震震中处，可观测到北西走向的地震丛集现象，与区域内已知断层分布并不一致.成像结果显示，在地壳浅部，背斜之间低缓区内的S波(V_S)速度结构存在横向分区特征，中北部地区表现为明显的高速异常，对应的波速比(V_P/V_S) 值较低，且大部分地震分布在这些异常体内.但泸县M6.0地震震源区位于P波和S波的高、低速异常的交界地带.结合其他地质与地球物理研究，推测泸县地震发生在一条北西走向、以逆冲为主高角度的调节断层上.

Seismicity and three-dimensional crustal structure of the Luzhou region in the southern Sichuan Basin,China

In recent years, increases in seismic activity accompanied by hydraulic fracturing for producing shale gas have attracted widespread attention from the public, government, industry departments, and scientists. Using P- and S-wave travel times recorded by regional networks and portable seismic stations in Luzhou and adjacent regions between 2010 and 2021, we present new constraints on seismic relocation and shallow crustal structure with the double difference seismic tomography method. After relocation, most small-medium earthquakes occur at depths of 2~10 km. The seismicity seems to cluster in the low and gentle area between the Luoguanshan and Gufoshan anticlines, and the spatial-temporal variation of the clusters is apparent. There are also a few earthquakes clustering with a linear northwestern trending in both the Luxian M6.0 epicenter and the south region of the anticlines, which are not correlated with the northeastern trending of known faults of the study region. Our imaging shows clear lateral variation in S wave velocity (VS) in the shallow crust, and the central and northern regions between Luoguanshan and the Gufoshan anticlines where most earthquakes has occurred obvious high VS anomaly, and the corresponding VP/VS ratio is also low. The Luxian M6.0 earthquake is located both in the P and S wave high-speed and low-speed transition zone. Combined with the previous geological and geophysical studies, it is inferred that the Luxian M6.0 earthquake occurred on a high-angle, thrust-based adjustment fault with NW trending.