【摘要】 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。更多还原

【Abstract】 The mobile seismic broadband stations we deployed in the Songpan-Ganzi and Longmenshan blocks during October 2005 to April 2007 just cross the earthquake source area Yingxiu,which gives us a good opportunity to study the deep crustal structure.In the observation profile from Longquanshan of Chengdu through Dujiangyan and Wolongshan to Xinduqiao,about 400km long,there were 34 mobile broadband seismic stations,with the station interval of 5～10km.They recorded 542 teleseismic seismic events more than M_S5.5 were 542,including 195 earthquakes more than or equal to M_S6.0.In this paper,by using the teleseismic P waveform data of the profile and in combination with the analysis of seismic tectonic background,the deep crustal structure around the source zone of the 2008 Wenchuan M_S8.0 earthquake was studied with the receiver function method.Our study results are as follows :(1)in the depth of 20 ～60km of the Songpan-Ganzi block and the Longmen Mountains nappe there is about 15～20km thick low velocity middle crust in which detachment structures readily occur,while such a low-velocity layer does not exist within the Sichuan Basin;and(2)the Moho depth increases from about 36～ 40km in the Yangtze Basin,about 50km in the Longmenshan belt to about 62～ 65km in the central part of the Songpan-Ganzi block,although decreases to 60km on the another side of the Xianshuihe fault zone,which shows that there should be a sudden change zone of crust thickness between the Yangtze Basin and the Longmenshan-Songpan-Ganzi block. It follows that the Songpan-Ganzi block and the Yangtze block should be a collision contact and that the Longmenshan nappe should the result of the upper crustal thrust movement.更多还原