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对龙门山及其邻近地区20个宽频带地震台站的记录提取远震P波接收函数,并应用H-k叠加方法,求得每个台站下方的地壳厚度和波速比.以此为约束,进一步作接收函数反演,获得各个台站下方的S波速度结构.后龙门山与松潘-甘孜地块的地壳速度结构相似,而前龙门山的地壳速度结构则与四川盆地相似.由此说明,中央主断裂带是青藏高原东部与扬子地块之间主要的边界断裂.松潘甘孜地块至后龙门山中南部地区存在下地壳低速层,有利于中上地壳物质的滑脱作用.远震接收函数和布格重力异常的分析结果支持龙门山断裂带深部构造为滑脱-逆冲型的论断.在松潘-甘孜地块内可能具有双层的滑脱构造.上层滑脱发生在10~15km的深度上,该滑脱带表现为高温韧性滑脱剪切带.下层滑脱则发生在30km左右的深度上,其下方为青藏高原东部广泛存在的下地壳流.布格重力异常的分析表明,在中上地壳,四川盆地的密度较高,松潘-甘孜地块密度相对较低.龙门山断裂带位于密度较高的一侧,是松潘-甘孜地块向东南方的四川盆地逆冲的结果.在地壳下部,四川盆地为高P波速度和高密度区,表明地壳物质是坚硬的.松潘-甘孜块体是低S波速度和低密度区,表明物质比较软弱.高密度块体阻挡了青藏高原东部下地壳物质向四川盆地下方的流动.受印度板块往北运动的影响,青藏高原下地壳物质向东流动.中上地壳物质向东运动受到刚性强度较大的扬子地块的阻挡,在龙门山断裂带上产生应力集中,导致中央断裂带上应力突然释放,产生汶川Ms8.0级地震.
Teleseismic P-wave receiver functions were extracted from records of 20 broadband stations in Longmenshan and its adjacent areas, and the Hk superposition method was used to obtain the crustal thickness and wave velocity ratio below each station. As a constraint, further For the inversion of receiver function, the S-wave velocity structure beneath each station is obtained.The crustal velocity structure of Houmenmen and Songpan-Garzê block is similar to that of the former Longmenshan, which is similar to that of Sichuan Basin.Thus, The central main fault zone is the main boundary fault between the eastern Qinghai-Tibet Plateau and the Yangtze block.The low-velocity crust beneath the Songpan-Ganzi block to the central-southern Longmen Mountains is favorable for the detachment of middle- and upper crustal materials.The teleseismic receiver function and cloth The results of grid gravity anomalies support the assertion that the deep part of the Longmenshan fault zone is a slippage-thrusting type, and may have a double-layer slippage within the Songpan-Garzê block.The upper slippage occurs at a depth of 10-15 km, The belt shows the high-temperature ductile shear zone.The lower slippage occurs at a depth of about 30km, and the lower crustal flow is widespread in the eastern Qinghai-Tibet Plateau beneath. The Bouguer gravity anomaly analysis table In the middle and upper crust, the density of Sichuan Basin is relatively high, and the density of Songpan-Garzê block is relatively low. The Longmenshan fault zone is located on the higher density side and is the thrust of the Songpan-Garzê block to southeastern Sichuan Basin Results In the lower part of the crust, the Sichuan Basin is characterized by high P-wave velocities and high densities, indicating that the crustal material is hard, and the Songpan-Ganzi block is characterized by low S-wave velocities and low densities, indicating a relatively weak mass. The movement of the lower crust beneath the eastern Qinghai-Xizang Plateau to the lower part of the Sichuan Basin was affected by the northerly movement of the Indian plate, with the lower crustal material flowing eastward over the Qinghai-Xizang Plateau. The eastward crustal movement was blocked by the more rigid Yangtze block , Resulting in stress concentration on the Longmen Shan fault zone, resulting in the sudden release of stress on the central fault zone, resulting in the Wenchuan Ms8.0 earthquake.