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2005年10月至2007年4月,我们在松潘-甘孜、龙门山地块布设的流动地震台阵观测剖面正好经过地震震源区映秀,这为研究地震震源区深部结构提供很好的机会。观测剖面自成都龙泉山,途经都江堰、卧龙,终止于新都桥,全长约400km,台站间距5～10km,34个流动宽频带地震仪共记录到该时间段内5.5级以上远震事件542个,大于等于6.0级为195个。利用该观测剖面记录到的远震P波波形资料,采用接收函数方法来研究汶川M_s8.0级地震震源区地壳深部结构,结合地震构造背景的分析,探讨引起这次地震的动力学模式,并由此认识汶川地震的孕育与成因机制。根据震源区地表破裂和余震分布及深部结构的综合分析,可以划出震源区下方的地震断裂带。主要研究结果表明:1)根据界面分布特征,发现松潘-甘孜地块及龙门山推覆体中在20～60km深度存在一个厚度约15～20km的低速中地壳,而四川盆地地壳内不存在低速层。该中地壳内的低速层,是引起中上地壳的推覆运动的滑脱层。2)Moho面自扬子盆地(36～42km)跨龙门山(50km)到松潘-甘孜腹地(62～65km)逐渐加深,跨鲜水河断裂又变浅(60km),说明横跨扬子盆地—龙门山—松潘-甘孜地块的该断裂带是地壳厚度的陡变带。该结果揭示了松潘-甘孜地块与扬子地块是碰撞接触模式,龙门山的推覆构造就是上地壳逆冲的结果。
From October 2005 to April 2007, the observational profile of the mobile seismic array deployed in the Songpan-Garze and Longmenshan plots passes through Yingxiu, an earthquake focal region, providing a good opportunity to study the deep structure of the focal region of the earthquake. The observation section from Longquan Mountain, Chengdu, passes through Dujiangyan and Wolong and terminates at Xinduqiao with a total length of about 400km and a station spacing of 5 ~ 10km. A total of 34 mobile broadband seismometers recorded a teleseismic event of magnitude 5.5 or above during this period 542, greater than or equal to 6.0 to 195. The cross-sectional observation using a recorded teleseismic P waveforms data using receiver functions to study deep crustal structure M_s8.0 Wenchuan earthquake focal region, the background binding assay configuration earthquake, the earthquake induced investigate kinetic mode, and In this way, we can recognize the cause and mechanism of the Wenchuan earthquake. According to the comprehensive analysis of surface rupture, aftershock distribution and deep structure in the source area, the seismic fault zone below the source area can be drawn. The main results show that: 1) The distribution interface, found Songpan - Ganzi block and nappe present in from about 15 to low speed in a crust thickness of 20 60km 20km ~ depth, while the low speed is not present in the earth’s crust Sichuan Floor. The low-velocity layer in the middle crust is a skidding layer that causes the mid-upper crustal nappe movement. 2) The Moho surface extends gradually from Longmen Mountain (50km) to the hinterland of Songpan-Ganzi (62 ~ 65km) from the Yangtze Delta (36 ~ 42km) to shallow and shallow (60km) across the Xianshui River, The fault zone of the Shan-Songpan-Garze block is a steep change in crustal thickness. This result reveals that the Songpan-Garzê block is a collision contact with the Yangtze block, and that the Longmen Shan nappe structure is the result of the upper crustal thrust.