汶川地震(Ms8．0)地表建筑体变形特征及其构造意义

SURFACE BUILDING DEFORMATION CAUSED BY WENCHUAN EARTHQUAKE ( M_s8.0 ) AND ITS TECTONIC IMPLICATIONS

通过汶川地震震区大量的实地考察已证实沿着早先活动断裂主要发育了两条地表破裂带:一条是沿着映秀-北川断裂产生的逆冲伴随右旋走滑破裂带,长275km,最大垂直位移达11m,水平位移达12m;另一条纯逆冲性质的破裂带,沿着灌县-安县断裂发育,最大垂直位移达4m。活动断裂之上的地表破裂带是野外工作中确定地震断裂性质的重要现象。另外,在活动断裂相邻区域和远离区域的路面以及建筑体还大量存在变形现象。通常沿活动断裂产生的地表破裂是典型的同震破裂,相邻区域的地表路面及建筑体发育的变形属于次生变形,远离区域发育的变形则属于震后变形。对次生变形和震后变形测量数据的应用容易影响活动断裂特征的确定和性质的判断,因为路面等建筑体上的挤压拱起、叠置以及水平错断等现象多是受到地震过程中通过断裂活动突然释放的巨大能量作用在局部地表建筑体产生的变形。但是,分布广泛的挤压现象暗示了区域上挤压应力场环境,有利于地表同震破裂位置的推测及地震断裂性质的判断。

At 2 ： 28pm, May 12, 2008, a devastating Ms8. 0 earthquake struck the Longmenshan area,the eastern margin of the Tibet. Based on detailed and comprehensive field survey, two surface ruptures have been discovered along the previous active faults. One is the 275km long surface rupture characterized by dextral-slip thrusting along the Yingxiu-Beichuan fault,with the maximum vertical throws of llm and horizontal heaves of 12m. Another is the 80km long surface rupture characterized by pure thrusting along the Guanxian-Anxian fault, with the maximum vertical throws of 4m. Surface rupture produced directly by the active faults is important phenomenon to find out the character of the faults. Synchronously, there are large numbers of deformation on the road surface and buildings neighboring and far from the active faults. The surface ruptures along the active faults is typical co-seismic ruptures, the deformations neighboring the active faults are sub-deformations, and those far from the active faults are post-seismic deformations. The sub-deformations and post-seismic deformations including ridge, overlapping, and horizontal displacements on the road and buildings, which are formed by local stress from the abrupt energy releasing through the activity of the faults. Therefore, sub-deformations and post-seismic deformations may not be directly used to determine features of active faults. But the far-ranging compressive deformation illustrates the compressive setting,which is propitious to understand surface rupture position and characteristics of seismicity faults.