青海玉树Ms7.1级地震同震地表破裂构造

    Structural analysis of the co-seismic surface ruptures associated with the Yushu Ms7.1 earthquake, Qinghai Province

    • 摘要: 分析了青海玉树Ms7.1级地震中形成的同震地表破裂分布与构造特征。本次地震造成的地表破裂长达46km,地震造成240cm的最大相对水平走滑错动量,最大垂直错动量60cm。地表破裂所经之处可看到原有断层新近活动的明显迹线。依次分析了按空间尺度划分的4个层次破裂的走向变化、同级破裂排列、破裂末端变化等构造特征。Ⅰ级破裂作为本次地震产生的整个破裂带,总体走向119°,由3段自然分开、左阶斜列的Ⅱ级破裂组成。3段Ⅱ级破裂自NW向SE依次为隆宝镇段、结古镇段和禅古寺段,破裂性质总体以左旋走滑为主,各段略有不同。各Ⅱ级破裂带内部,分别由若干Ⅲ级破裂段落组成,总体呈现右阶斜列排列模式。Ⅲ级破裂本身由一系列简单的Ⅳ级破裂雁列或羽列右阶斜列构成。不同层次的地表破裂具有简单剪切构造带的变形特征,共识别出R、R’、Y、T和P五组基本破裂面。其初始破裂面展布特征可以用库伦破裂准则来解释,其中岩土体材料的内摩擦角大致为26~44°。各级破裂端部出现分叉、转向及逐渐消失等变形特征。

       

      Abstract: The Yushu Ms7.1 earthquake in Yushu area, Qinghai Province, China, caused a 46km-long surface rupture, with a maximum horizontal left-slip displacement of 240cm and a maximum vertical displacement of about 60cm. The surface rupture distributed along the pre-existing Garzi-Yushu active fault.Four levels of ruptures can be classed on different scales and structural characters. They are level Ⅰ, Ⅱ, Ⅲ and Ⅳ from large scale to small one in sequence. Level Ⅰrupture, the surface rupture as a whole caused by this earthquake, generally strkes E119°S and comprises three level Ⅱ ruptures, i.e. Longbao Town Section, Jiegu Town Section and Changu Temple Section respectively from the northwest to southeast. A level Ⅱ rupture usually consists of a dozen of level Ⅲ ruptures. Level Ⅳ rupture is the smallest one which can be figured out on the ground in the field survey. Tens or hundreds of level Ⅳ ruptures constitute a level Ⅲ rupture. Different levels of rupture may have different mode in arrangement, with a left step among the Level Ⅱ ruptures and a right step mode among both level Ⅲ and Ⅳ respectively. However, different level ruptures have the similar character of the Riedel Shear structures and five basic shear planes, R, R’, Y, T and P, can be identified. The angles of internal friction of the initial fault plane is 26~44°according to Coulomb failure criterion.

       

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