中文摘要：

根据龙门山及其周边地区（26°～35°N，98°～109°E）的132个台站的宽频带远震记录，使用H-k叠加方法计算地壳厚度和波速比。结果表明该区域的地壳厚度总体变化是：从东向西增加，东部的最小厚度为37．8km，西部的最大厚度是68．1km，其中横跨龙门山断裂带的地壳厚度变化最大，从东南的41．5km增加到西北的52．5km。根据Airy均衡理论，用台站的高程和观测地壳厚度数据求得最小二乘意义下的壳幔密度差为0．649g／cm^3，平均地壳厚度为37．9kin。龙门山及其邻近地区基本上处于均衡状态。松潘一甘孜地体北部和西秦岭造山带具有低泊松比（v〈0．26），扬子地台的西南部具有低-中泊松比（v〈0．27），松潘-甘孜地体南部、三江褶皱带和四川盆地具有中-高泊松比（0．26≤v≤0．29）。该地区的泊松比空间分布不支持青藏高原东部广泛分布的下地壳流的假说。龙门山断裂带南段及其附近地区的高泊松比（v≥0．30）可以看成是地壳具有较高的铁镁质组分和／或存在部分熔融。该地区下地壳可能是处于富含流体和温度较高的部分熔融状态。松潘-甘孜块体南部的上地壳物质向东运动，受刚性强度较大的扬子地台的阻挡，导致沿龙门山断裂带产生应变积累。当断层被地壳流体弱化，积累的应变能量快速释放，产生汶川Ms8．0地震。

英文摘要：

On the basis of the broadband teleseismic data recorded at 132 seismic stations in Longmenshan Mountains and adjacent regions （26° -35°N ,98° -109°E） , the crustal thicknesses and Poisson＇s ratios were estimated by the H-k stacking method. The general trend of the crustal thickness variation appears an increase from east to west,with a minimum thickness of 37.8km and a maximum thickness of 68. 1km. Across the Longmenshan fault zone（LSFZ） from southeast to northwest,the crustal thickness increases sharply from 41.5km to 52.5km. According to Airy＇s isostatic hypothesis and on the basis of the crustal thickness obtained from the H-k stacking, the density contrast between the crust and the uppermost mantle and the mean crustal thickness were estimated to be 0.649g/cm^3 and 37.9km,respectively. The isostatic anomalies suggest that the crust in Longmenshan Mountains and adjacent regions is basically in an isostatic state. The results also show that the Northern Songpan-Garze terrane and the Western Qingling orogenic belt have low Poisson＇s ratios（v〈0.26） ,the south Western Yangtze platform has low-tointermediate Poisson＇s ratios（t,〈0.27）,and the Southern Songpan-Garze terrane,the Sanjiang fold system and the Sichuan Basin have high-to-intermediate Poisson＇s ratios （0.26 ≤v≤ 0.29 ）. The distribution pattern of Poisson＇s ratios does not support the hypothesis of widespread lower crust flow in the eastern Tibetan Plateau. High Poisson＇s ratios （ v≥ 0. 30 ） in the south segment of LSFZ and its neighboring areas can be regarded as the evidence for the existence of more mafic composition and/or partial melting. The lower crust in the Southern Songpan-Garze terrane may be liquid-rich and in the state of high temperature and partial melting. The eastward movement of the upper crust is obstructed by the more rigid Yangtze platform. When the fault was weakened by the crustal fluid, the accumulated stain energy was released through the Longmenshan fault zone, and so the Wenchuan