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基于2007年1月～2010年8月自贡地方数字测震台网和流动台站记录的地震观测报告,对自贡-隆昌地区开展了地震精定位和速度结构反演两方面的研究工作,并结合研究区地震活动时间序列及注水井(家33井)的加压数据,探讨了注水区域及邻区地震震源深度分布、P波速度结构特征及其与家33井加压注水的关系。定位结果显示:地震的空间丛集性更加明显,集中分布在自贡(A区)、富顺-隆昌交界(B区)及隆昌(C区)等3个区域。其中距家33井西侧约20km的A区地震呈NNE向长轴展布,震源深度主要分布在5～15km;B、C区域内的地震则沿NW向长轴展布,家33井所在的B区绝大多数地震的震源深度在2～6km,即家33井的注水层位附近,呈现由NW至SE的铲形特征,并逐渐变深;位于家33井东南方向约15km的C区,地震震源深度相对B区较深,优势深度在8～15km。分析认为,A区地震活动与家33井加压注水无关,而B、C区域的地震活动却明显受到加压注水的影响。P波速度结构显示:在3km深的注水层位附近,区域B、A之间形成了1条近NS走向的高、低波速过渡带,B区地壳介质的P波速度明显高于A区,其原因是家33井出现容腔饱和,使该区地下介质具有较高含水饱和度引起的。
Based on the seismological observations recorded by Zigong local digital seismograph stations and mobile stations from January 2007 to August 2010, the authors carried out researches on the precise positioning of seismograms and velocity structure inversion in Zigong-Longchang area, combining with The time series of seismic activity in the study area and the pressure data of injection well (Well 33), the depth distribution of seismic focal depth and the characteristics of P-wave velocity and the relationship between them and the pressurized water injection in Well 33 were studied. Positioning results show that the spatial clustering of earthquakes is more obvious and concentrated in three areas: Zigong (A zone), Fushun-Longchang border (B zone) and Longchang (C zone). The A-zone earthquakes of about 20km west of Jijia 33 well are distributed along the long axis of NNE with focal depths of 5 ~ 15km. The earthquakes in B and C are distributed along the long axis of NW, The depth of focal depth of the vast majority of earthquakes in Area B is 2 ~ 6km, that is, the water level near the well of Well 33 is a shovel-shaped feature from NW to SE, and gradually deepens. In the C The focal depth of the earthquake is relatively deeper than that of the B zone, with the dominant depth of 8-15 km. The analysis shows that the seismic activity in Area A is not related to the pressurized water injection in Well Jia 33, but the seismic activity in areas B and C is obviously affected by pressurized water injection. The P wave velocity structure shows that near the waterflooding horizon of 3 km depth, there is a transition zone near the NS with high and low velocity in the region B and A, and the P wave velocity in the B zone crustal medium is obviously higher than that in the A zone. The reason is that the well in chamber 33 is saturated, which causes the underground medium in this area to have high water saturation.