2010年青海玉树地震(Ms7.1)同震地表破裂及其与山脉隆升的关系

摘要

In field investigation we found that Qinghai Yushu Ms7.1 earthquake occurred on April 14, 2010 produced a～65 km long co-seisrme surface rupture zone which strikes 310° and dips NE. The entire zone is composed of two parts: the west section is about 19 km long and the east section is 30 km. Between these two sections, a 15 km long zone surface rupture gap is observed. Surface ruptures displayed common sinistral lines mainly featuring right stepping en-echelon ruptures, while vertical offsets developed. The ratios between co-seismic vertical offset and horizontal offset range from 0.13 to 0.53, while the geomorphic dv/dh values of 0.27～0.63 are close to co-seisrnic dv/dh (0.13～0.53), indicating that the Yushu Nanshan uplift probably showed the same kinematic and dynamic characteristics. In other words, the Yushu Nanshan uplift is resulting from the cumulative vertical offsets produced by many earthquakes similar to Yushu earthquake along Yushu fault in the geological history. We conclude that we need 1800～2600 earthquakes similar to Yushu earthquake to form Yushu Nanshan. Former researchers reckon the recurrence period of the Yushu section of GanziYushu fault zone to be 120-200 years, which would make us believe that this fault section's activity started from 200～400 ka ago.%野外调查发现,2010年4月14日青海玉树Ms7.1级地震同震地表破裂带长约65km,破裂带走向为310°,破裂面向NE陡倾,地表破裂带由2部分组成,其中西侧部分长约19km,东侧部分长约30km,两者之间存在约15km的无破裂区.地表破裂以右阶雁行状破裂分布为主要特征,呈现左旋走滑性质,伴随有垂直位移.统计结果显示,同震地表破裂垂直位移(dv)与水平位移(dh)的比值在0.13～0.53之间,地貌累积dv与累积dh比值为0.27～0.63.同震dv/dh与地貌dv/dh的相似显示玉树南山的形成和玉树地震具有同样的运动学和动力学性质,玉树南山的形成是地质历史上沿玉树断裂多次类似于玉树地震的地震活动的结果,计算出需要1800～2600次地震才能造成玉树南山的隆升.前人研究本段断层地震复发周期为120～200年,计算出断层开始活动时间不晚于20万～40万年以前.