汶川地震北川县城地表断层破裂特征
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摘要
2008年5月12日四川省汶川8.0级地震是由于青藏高原的挤压应力在龙门山断裂集中释放。北川位于龙门山断裂的北段,野外考察结果表明,在主断裂方向北川县城可观测到两条断裂,并且产生了明显的地表破裂,走向均为北东30°～50°,主断裂方向地表破裂约10 km,具有明显挤压逆断层特征,上盘以60°～80°高角度向北东逆冲,断层垂直位移量3～4m,水平位移量0～2 m。主断裂的地表破裂集中位于两个地层的不整合面上,上盘为寒武系细砂岩、砂页岩,下盘为泥盆系白云岩、白云质灰岩。另外在北川县城北部发现次级断裂一条,走向北西30°,地表破裂长度约4 km,表现为正断层特征。这些破裂都直接或间接受地下深部构造的控制。
On the May 12th 2008,Wenchuan MS 8.0 earthquake broke out as a result of compressive stress of Qinghai-Tibet Plateau released in Longmenshan Fault.Beichuan is located in the northern section of the Longmenshan Fault.Fieldwork results show that there were two main faults in Beichuan County,which caused obvious ground rupture.The trend is 30°～50°,and the total length of the ground rupture zone in Beichuan County is about 10km.It has obvious characteristics of extrusion thrust fault.The thrust fault thrashed at high angle 60°~80 °.The vertical displacement on the ground along the rupture zone is about 3～4 m,and the horizontal displacement is about 0～2 m.The lithology of the hanging wall is fine-grained sandstone,sandstone and shale in Cambrian,and dolomite,dolomitic limestone of Devonian in foot wall.The main ground rupture is located at the boundary of two stratums.In addition,there was a sub-fault in the north of Beichuan County,which was a normal fault.Its trend is 30°,and the length of the ground rupture zone is about 4 km.These ground ruptures are directly or indirectly controlled by the structure of underground.
On the May 12th 2008,Wenchuan MS 8.0 earthquake broke out as a result of compressive stress of Qinghai-Tibet Plateau released in Longmenshan Fault.Beichuan is located in the northern section of the Longmenshan Fault.Fieldwork results show that there were two main faults in Beichuan County,which caused obvious ground rupture.The trend is 30°～50°,and the total length of the ground rupture zone in Beichuan County is about 10km.It has obvious characteristics of extrusion thrust fault.The thrust fault thrashed at high angle 60°~80 °.The vertical displacement on the ground along the rupture zone is about 3～4 m,and the horizontal displacement is about 0～2 m.The lithology of the hanging wall is fine-grained sandstone,sandstone and shale in Cambrian,and dolomite,dolomitic limestone of Devonian in foot wall.The main ground rupture is located at the boundary of two stratums.In addition,there was a sub-fault in the north of Beichuan County,which was a normal fault.Its trend is 30°,and the length of the ground rupture zone is about 4 km.These ground ruptures are directly or indirectly controlled by the structure of underground.
引文
[1]张勇,冯万鹏,许力生.年汶川大地震的时空破裂过程[J].中国科学,2008,38(10):1186-1194.
[2]董树文,张岳桥,龙长兴.四川汶川8.0地震地表破裂构造初步调查与发震背景分析[J].地球学报,2008,29(3):392-396.
[3]邓志辉,杨主恩,孙昭民.四川汶川MS8.0级地震北川-映秀地表破裂的复杂现象[J].2008,53(20):2509-2513.
[4]王阎昭,王恩宁,沈正康.基于GPS资料约束反演川滇地区主要断裂现今活动速率[J].中国科学,2008,38(5):582-597.
[2]董树文,张岳桥,龙长兴.四川汶川8.0地震地表破裂构造初步调查与发震背景分析[J].地球学报,2008,29(3):392-396.
[3]邓志辉,杨主恩,孙昭民.四川汶川MS8.0级地震北川-映秀地表破裂的复杂现象[J].2008,53(20):2509-2513.
[4]王阎昭,王恩宁,沈正康.基于GPS资料约束反演川滇地区主要断裂现今活动速率[J].中国科学,2008,38(5):582-597.
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