摘要
汶川Ms8.0强烈地震发生在一条现今并不活动的龙门山构造带上,造成了以汶川、映秀为中心及其周边地域的严重破坏和人员的重大伤亡.然而强烈震发生前却未见有可能的确切征兆或浅表层异常活动,即浅层过程与地震发生的深层过程并不匹配.为此对这次强烈地震"孕育"、发生和发展的深层过程进行了分析和探讨,初步研究表明:①在印度洋板块与欧亚板块陆—陆碰撞、挤压作用下,喜马拉雅造山带东构造结向NNE方向顶挤、楔入青藏高原东北缘,迫使高原深部物质向东流展,在受到以龙门山为西北边界的四川盆地阻隔下,一部分物质则转而向东南侧向运移;②龙门山地带在地形上差达3500±500m左右,而地壳厚度在龙门山西北部为60±5km左右,四川盆地为40±2km左右,而龙门山地带与其东、西两侧相比则为地壳厚度变化幅度达15～20km的突变地域,即为应力作用的耦合地带;③中、下地壳和地幔盖层物质以地壳低速层、低阻层(深20～25km)为第一滑移面,以上地幔软流层顶面为第二滑移面,且在四川盆地深部"刚性"物质阻隔下,深部壳、幔物质以高角度在龙门山构造带和四川盆地的耦合地带向上运移(或称逆冲),且在龙门山地表三条断裂构成的断裂系向下延伸到20km左右深处汇聚,二者强烈碰撞、挤压、震源介质破裂;在物质与能量的强烈交换下,应力得到释放,故形成了这次Ms8.0强烈地震.为此从深部初步揭示了这次强烈地震"孕育"、发生和发展的深层动力过程.
The Wenchuan Ms8.0 earthquake of 2008 occurred on the Longmenshan tectonic zone which seems not very active from available data. And it is reported that no noticeable precursors have been observed before the event. It might imply that the crustal deformation at depth associated with this gigantic shock had no expression on the surface or shallow subsurface which was detectable. In this article, we attempt to analyze the processes of brewing and generation of this event at depth that can account for the reason of this devastating earthquake. Tectonically, it is obvious that the India-Eurasia plate collision serves as the most important dynamic setting of major earthquakes in southwestern China. The eastern end of the Himalayan chain is moving rapidly in NNE direction into the Tibetan plateau, forcing deep material to flow toward east. Due to the obstruction of the NE trending Longmenshan tectonic zone in the northwestern margin of the Sichuan basin, the partial flow turns to southeast. Longmenshan is a conspicuous boundary of topography and crust structure, across which the elevation difference is as large as 3500±500 m, with crustal thickness 60±5km in its west and 40±2 km in its east, respectively. Thus it must experiences intense deformation and stress accumulation, though very slow without appreciable manifestation. Based on available data, it is inferred that material of lower crust and covering strata of upper mantle is flowing eastward along two deep slide surfaces, of which one is the layer of low-velocity and low-resistivity （20 - 25 km depth）, and the other is the top of mantle asthenosphere. Hindered by rigid mattter beneath the Sichuan basin, the flow of lower crust and covering strata of upper mantle material turns overthrusting at high angles at the Longmenshan. On the other hand, three thrust faults visible west of the Longmenshan extend downward to depth 20 km, where they converge into one active zone. Thus the Longmenshan tectonic zone is a place where occurs the coupling between slippage o
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2008年第5期1385-1402,共18页
Chinese Journal of Geophysics
基金
国家973项目
中国科学院知识创新工程重要方向项目(KZXCX3-SW-148)联合资助
关键词
汶川地震
物质运移
深层过程
汇聚地带
动力学响应
Wenchuan earthquake, Material flow, Deep process, Convergence zone, Dynamic response
