【摘要】 2008年5月12日汶川8.0级大地震发生在青藏高原东缘龙门山推覆构造带上,除映秀—北川断裂、灌县—江油断裂上各形成240 km和72 km长的地表破裂带外,可能在成都平原西部的什邡市师古镇附近形成一条弱地表破裂带.成都平原内的地震地表破裂带与龙门山区的2条地震破裂带构成倾向北西的叠瓦状逆断裂地震地表破裂系统.野外调查发现,师古镇南肖家院—庆云庵建筑物严重破坏带、水渠跌水、地表褶皱、喷砂和地裂缝带走向30°,延伸长度约7.5 km.探槽开挖表明,地表地震褶皱陡坎下的地层发生弯曲变形,汶川地震使断层上盘的地面和最新地层褶皱隆起0.2 m.TC2探槽中的粘土层底面褶皱隆起0.4m,它可能记录到汶川地震之前另外一次与汶川地震大小相当的古地震事件.浅层地震勘探资料表明,平原区出现地震地表破裂的位置不仅存在晚更新世活动断裂,而且.伴生有第四纪活动褶皱.更多还原

【Abstract】 The 12 May 2008 Wenchuan M_s8. 0 earthquake occurred on the Longmen Shan (Mountains) thrust-nappe structure zone in the eastern margin of the Tibetan plateau. It has produced 240 km long and 72 km long rupture zones on the surface along the Yingxiu-Beichuan fault and Guanxian-Jiangyou fault, respectively, which are branches of the Longmen Shan fault system. Besides, our field investigation found that this shock has also caused a weak rupture zone on the ground nearby the Shigu town, Shifang city that lies in the western Chengdu plain east to the epicenter. This rupture zone and the other two ruptures in the Longmen Shan mountainous area aforementioned constitute a northwest-dipping imbricate structure. It is about 7. 5 km long, trends in 30°, manifested by a series of directed deformation phenomenon such as damages of buildings, channel dislocations, ground folds, erupted sand and earth fissures on the surface. Observations in the exploratory trenches indicate that there is a fold uplift of 0. 2 m in the youngest strata (including the surface) produced by the Wenchuan M_S 8. 0 event, and a fold uplift of 0. 4 m in the clay bottom in the trench, presumably resulted from a paleoearthquake of similar size to the Wenchuan shock in 2008. Seismic exploration to shallow subsurface demonstrates that in the place of the Chengdu plain with the found seismic rupture zone exists active faults of the late Pleistocene as well as active folds of the Quaternary.更多还原