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自贡-隆昌地区地震重新定位及P波速度结构研究
张致伟1, 程万正1, 吴朋1, 宫悦1, 陈文康2, 许艳2, 周秀忠3
1.四川省地震局,成都市人民南路三段29号610041;2.自贡市防震减灾局,四川自贡643000;3.成都地震基准台,成都611730
摘要:
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。
关键词:  自贡-隆昌地区  加压注水  双差定位  联合反演  速度结构  
DOI:
分类号:
基金项目:地震科技星火计划项目(XH1021Y)、中国地震局监测预报司震情跟踪定向工作任务(2012020107)及国家自然科学基金项目(41090294)共同资助
Study on earthquake relocation and P-wave velocity strcture in the Zigong and Longchang area
Zhang Zhiwei1, Cheng Wanzheng1, Wu Peng1, Gong Yue1, Chen Wenkang2, Xu Yan2, Zhou Xiuzhong3
1.Earthquake Adiministration of Sichuan Province, Chengdu 610041, China;2.Earthquake Adiministration of Zigong City, Zigong 643000, Sichuan, China;3.Chengdu Seismic Station, Chengdu 611730, China
Abstract:
Based on earthquake observation report recorded by the Zigong local digital seismic network and mobile stations from January 2007 to August 2010, the earthquake relocation and velocity structure inversion are developed in the Zigong and Longchang area. Taking into account the time series of seismic activities and injection pressure of water injection well (Jia 33 well) in study area, we discuss the focal depth distribution, the characteristics of P-wave velocity structure and relationship with injection pressure of Jia 33 well in and around injection region. The positioning result shows that the earthquake space cluster distributions are more obvious, the earthquakes are concentrated in three cluster regions of Zigong (region A) , Fushun-Longchang juncture (region B) and Longchang (region C). Region A is about 20kin to the west of Jia 33 well, earthquakes distribute along NNE direction, and the dominant range of focal depth is 5 15kin. Earthquakes distribute along NW direction in regions B and C. Region B is where Jia 33 well locates in, the focal depth of most earthquakes are between 2km and 6km, which is near the affusion layer of Jia 33 well. The focal depth presents shovel-shaped distribution characteristic which spreads from NW to SE, and then become gradually deep. Region C is about 15kin to the southeast of Jia 33 well. The focal depth in region C is relatively deeper than that in region B. The dominant depth is 8 - 15kin. The seismic activities of region A are independent of injection pressure of Jia 33 well. However the injection pressure of Jia 33 well has obvious regulatory effect on seismic activities of Rgions B and C. The P-wave velocity structure shows that near the affusion layer at the depth of 3km, there is a near NS direction transition zone of high-and-low velocity between regions B and A. P-wave velocity in region B is higher than that in region A. We make the conclusion that the significantly increased P-wave velocity in region B results from the higher water saturation of underground medium by square-cavity saturation of Jia 33 well and it has a correlation with injection pressure of Jia 33 well.
Key words:  Zigong and Longchang area  Injection pressure  Double-difference  Algorithm simultaneous inversion  Velocity structure