四川汶川8.0级地震地表破裂与震害特点

SURFACE RUPTURE AND HAZARD CHARACTERISTICS OF WENCHUAN EARTHQUAKE WITH MAGNITUDE 8.0 IN SICHUAN PROVINCE

2008年5月12日四川汶川8.0级地震发生在青藏高原东缘的龙门山构造带上。通过野外实地调查与测量发现,汶川8.0级地震的地表破裂发生在龙门山构造带中的北川—映秀断裂之映秀南西—平武南坝石坎子段,彭县—灌县断裂的都江堰向峨—安县桑枣段也同时发生了同震地表破裂。北川—映秀断裂上的地表破裂长约220 km,表现为逆冲–右旋走滑运动特征,最大同震位错在6 m左右,水平与垂直位错量大致相当,与先期的研究成果一致;彭县—灌县断裂上的同震地表破裂长约100 km,表现为右旋–逆冲运动特征,最大垂直位错在2 m左右,水平与垂直位错量之比为1∶1～1∶3。地震地表破裂的空间分布及同震位错特征表明,汶川8.0级地震系北川—映秀断裂的逆冲–右旋运动所导致,并同时牵动了彭县—灌县断裂发生同震地表破裂。地震灾害的特点主要表现为地震波导致的强地面运动破坏、地震地表破裂带直接撕裂、地震导致的次生地质灾害(如崩塌和滑坡等)摧毁或掩埋建(构)筑物和堰塞湖等。根据地震考察资料并参考InSAR和强震仪记录,勾绘的该次地震等震线长轴方向沿龙门山构造带呈N40°～50°E方向延伸,出现了3个XI度的破坏区,具单侧多点瞬间破裂的典型特征,导致了四川北部、甘肃和陕西南部地区灾害较正常地震衰减破坏的显著加重。

On May 12 of 2008, the Wenchuan M8.0 earthquake in Sichuan Province occurred on the Longmenshan tectonic belt at the eastern margin of the Qinghai-Tibet Plateau. Through field investigation and survey, the major surface rupture occurred on the segment of Beichuan-Yinxiu fault from the southwest of Yingxiu to Shikanzi of Nanba in Pingwu County, with a length of 220 km. It shows the fault produces a thrust and dextral slip The maximum displacement along the fault is about 6m; horizontal component is equivalent to the vertical direction. Another segment from Xiange in Dujiangyan City to Sangzao in Anxian County produces a 100 km coseismic surface rupture in length, also displaying a thrust and dextral characteristic of the fault. The maximum vertical displacement on this segment is about 2 m; and the ratio of the vertical component and the horizontal is between 1 ： 3 and 1 ： 1. The distribution of surface rupture and the characteristics of coseismic displacements show that the thrust-dextral slip of Beichuan-Yingxiu fault led to the Wenchuan M8.0 earthquake, representing strong ground motion destroy, surface cracking directly and secondary geological hazards（such as landslip, hillside creep） pulling down or burying the civic structures. Based on macroscopical survey, studies of InSAR, and records of seismographs, the axis of isoseismal line extends at N40° - 50°E orientation along the Longmenshan tectonic belt. Its typical characteristic is a unilateral, multipoint instantaneous rupture. The earthquake produced three intensity damaged areas with seismic magnitude XI, and remarkably enhanced the damages of normal earthquake attenuation in the North Sichuan province, the South Gansu Province and Hanzhong region of Shaanxi Province.