龙门山山前疑似汶川M_S 8.0地震地表破裂的浅层地震反射调查  

EXPLORATION OF SUSPECTED SURFACE RUPTURES OF THE M_S 8.0 WENCHUAN EARTHQUAKE AT FRONTAL AREAS OF LONGMENSHAN USING SHALLOW SEISMIC REFLECTION

作　　者：刘保金[1] 杨晓平[2] 酆少英[1] 寇昆朋[1] 

机构地区：[1]中国地震局地球物理勘探中心,郑州450003 [2]中国地震局地质研究所,国家地震活动断层研究中心

出　　处：《地震地质》2008年第4期906-916,共11页Seismology and Geology

基　　金：国家自然科学基金(40841020);地震行业科研专项(200808041);中国地震局汶川8.0级地震应急科学考察项目共同资助

摘　　要：2008年5月12日发生在龙门山构造带的汶川MS8.0大地震是映秀-北川断裂突发错动的结果。此次地震不但使NE向的映秀-北川断裂和灌县-江油断裂发生了地表破裂,而且,在成都平原区的什邡、绵竹等地也出现了不同程度的地表裂缝、公路拱曲以及带状的喷砂冒水现象。此项探测研究以出现在什邡市师古镇附近的疑似地震地表破裂带为切入点,通过采用可控震源以及高精度的浅层地震反射勘探方法,获得了深度15～800m范围内高分辨率的地下结构和构造图像。结果表明,在地表破裂之下存在向平原区逆冲的隐伏断层和反向的逆冲断层,地震过程中隐伏逆断层的活动可能是近地表地层出现褶皱变形和地表破裂的主要原因。The Ms 8.0 great Wenchuan earthquake of May 12th,2008 was generated by abrupt faulting of the Yingxiu-Beichuan Fault along the Longmcnshan Fault zone. The earthquake produced not only the surface ruptures along the Yingxiu-Beichuan Fault and Guanxian-Jiangyou Fault, but also surface rupture , highway＇s pavement arching,sand-boils and waterspouts in various degrees in the areas such as Shifang and Mianzhu of the Chengdu plain. To know the shallow geological structures under the surface rupture zone, a high-resolution shallow seismic reflection profile of 6350m long in near-EW direction was completed. This profile is located at the Shigu town, Shifang city, where a suspected earthquake surface rupture zone was discovered. In this study, a trace interval of 3m, shot interval of 18re,and a 300-channel 25-fold observation system was used. In order to give consideration of both near-surface reflections and dipping interface imaging, we adopted the split-spread geometry and asymmetrical zero-offset receiving technique. For suppressing random-noise and raising signal to noise ratio of seismic data, 30 times vertical stacking of vibrator signals was made for each common-shot gather after correlation of individual records. By using the above work method and spread geometry, we obtained high-resolution images of structures in the depth range of 15- 800m after data processing. The result shows that there are the buried thrust fault thrusting to the plain and the backthrust fault under surface rupture zone, and that the activity of the buried thrust fault may be the main causes for folding and deformation in near-surface strata and for the coseismic surface rupturing.

关 键 词：汶川MS8.0地震 地表破裂带 浅层地震反射剖面 隐伏逆断层 

分 类 号：P315.2[天文地球—地震学] TU413.62[天文地球—固体地球物理学]