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鲜水河断裂带南段深部变形的重复地震研究 被引量:18

Quantitative study of the deep deformation along the southern segment of the Xianshuihe fault zone using repeating microearthquakes
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摘要 利用2000—2013年四川数字地震台网和水库台网的波形资料以及川西流动台阵的事件波形,通过辨识发生在同一断层位置上的重复地震来定量研究鲜水河断裂带南段的深部变形.针对研究区台站分布稀疏的客观情况,应用了子采样条件下基于S-P相对到时差来约束震源位置一致性的方法,在鲜水河断裂带识别出11组重复地震,并利用连续波形资料进行了重复地震完整性的初步测试,同时运用结合波形互相关资料的双差法来完成研究区背景地震和重复地震位置的精确定位.重新定位后的地震图像展示研究区中上地壳存在明显缺震层,其与壳内的低速低阻层相吻合.利用重复地震的地震矩和重复间隔,估算出鲜水河断裂带南段孕震深部的滑动速率为3.0~10.2mm·a^-1,显示研究区不同地震构造区的深部滑动速率存在明显差异. Repeating earthquakes are a series of shocks regularly occurring at the same patch of a fault. They are commonly interpreted as repeated ruptures of a single asperity owing to the concentration stress due to aseismic slips in the surrounding areas. Deep slip rates along a fault can be estimated from coseismic slips of the repeating earthquakes, resulting in direct measurements of fault deformation at seismogenie depths. In this study, we used the waveform data recorded by the Sichuan digital Seismic Network (SSN) between 2000 and 2013,the Reservoir Seismic Networks(RSN) from 2008 to 2013, and West Sichuan Seismic Array(WSSN) from October 2006 to July 2009 to search for clusters of repeating earthquakes along the southern segment of the Xianshuihe fault zone. We then used them to investigate deep deformation of the fault zone. Using waveform cross-correlation analysis, we identified a total of 635 similar earthquake clusters including 357 doublets and 278 multiplets that consist of 3704 earthquakes in total. Most of sequences are aperiodic with recurrence intervals varying from a few minutes to hundreds of days. Due to the sparsity of the network in the study area, we used an empirical method to constrain the relative distance between event pairs based on S-P differential times measured at subsample accuracy. We used this method to identify a total of 11 sequences of repeating earthquakes along the southern segment of the Xianshuihe fault zone. We also utilized a temple matching technique to scan the continuous records to search for all the members of the repeating earthquake families and relocated all the background seismicity and repeating earthquakes using the double difference method with differential data measured with the cross correlation technique. The relocated seismicity suggests the existence of an aseismic layer in the upper crust or the middle crust, which is also featured by low seismic velocity and low electric resistivity. High seismicity is found in two depth ranges of ~0~13 km in the brittle upper crust and of ~25~50 km in the lower crust, respectively. The relocated seismicity shows possible existence of an eastward- inclining deep fault in the lower crust. Our results also suggest that the upper crust decouples with the lower crust at the top boundary of the lower-velocity zone (the aseismic layer), which leads to a listric thrust in the upper crust. The fault slip rate computed from the size and recurrence intervals of the repeating earthquake sequences varies from 3.0 to 10.2 mm · a^-1 at depths 3.6~18.7 km, and shows substantial differences among seismotectonic divisions.
出处 《地球物理学报》 SCIE EI CAS CSCD 北大核心 2015年第11期4138-4148,共11页 Chinese Journal of Geophysics
基金 中国地震局地震预测研究所基本科研业务专项(2015IES010203,2015IES0407) 国家自然科学基金(41104031,41474031)资助
关键词 鲜水河断裂南段 重复地震 深部滑动速率 地震定位 Southern segment of the Xianshuihe fault Repeating earthquakes Deep slip rates Earthquake relocation
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