玉树地震地表破裂特征及其破裂方式

北京时间2010年4月14日玉树Ms7.1级地震产生了长约50km的地表破裂带,地表破裂系统非常典型。本文通过对果庆益荣松多村附近河滩与结古镇西南河道两岸2个地表破裂点的野外观测和地表破裂的力学分析,探讨玉树地震地表破裂特征和方式。在果庆益荣松多村附近河滩地表破裂与地震陡坎呈间隔式左行右阶排列,具转换压缩性质;在结古镇西南河道北岸主地表破裂带中地表破裂非常发育,出露一处古断层面。地表破裂的野外调查与应力分析结果表明,玉树地震同震地表破裂带总体走向为125°,属于典型的左行走滑破裂带,最大左行走滑位移量1.75m,主压应力为近东西向,这一结果与美国地质调查局和中国地震局地震地球物理研究所公布的结果基本一致。

Characteristics and Patterns of Surface Ruptures Caused by the Yushu Earthquake

April 14, 2010 earthquake Yushu Ms 7.1 occurred near the Ganzi-Yushu fault zone,NWW direction, produced an about 50 km long surface rupture zone, which had typical broken styles. We choose two surface rupture points located at Guoqingyirongsongduo and the southwestern side of Jiegu Town, to explore the characteristics of surface rupture of the Yushu earthquake and the relationship between active fault and the surface rupture by stress analysis on the rupture phenomena at Guoqingyirongsongduo and statistical analysis on 426 surface rupture and field investigation and observation on the trench under the surface ruptures and ancient faults at the southwestern side of Jiegu Town. Field investigation and stress analysis results showed that the strike of the Yushu coseismic surface rupture zone is NW315°～SE125°, which is a typical pure-shear left-lateral strike-slip fault zone, with sinistral strike-slip displacement up to 1.75 m, while the fault dips to 120° direction. Transpression is the typical phenomenon of strike-slip fault developed at Guoqingyirongsongduo, which produced a small shape rift basin and block uplift. An ancient fault plane with occurrence of 30°∠80°, is exposed on the north shore of the river at the southwestern side of Jiegu Town. The principal stress direction is nearly EW which is consistent with focal mechanism solutions published by United States Geological Survey and Institute of Geophysics, China Earthquake. Parts of the earthquake surface ruptures and active faults do not coincide, and fault activity did not occur, we believe that the surface rupture is controlled by the relative faults, but the basic causes of the surface rupture is not caused by fault movement.