断层穿越斜坡场地效应分析:以绵竹九龙镇山前斜坡为例  

SITE EFFECTS OF SLOPE PASSED BY FAULT ON PGA,A CASE STUDY AT MIANZHU JIULONG TOWN

作　　者：王文沛[1] 李滨[2] 李洪涛[3] 

机构地区：[1]中国地质环境监测院,北京100083 [2]中国地质科学院地质力学研究所,北京100081 [3]中国地质调查局水文地质工程地质技术方法研究所,保定071051

出　　处：《工程地质学报》2015年第5期850-855,共6页Journal of Engineering Geology

基　　金："十二五"国家科技支撑计划项目(2012BAK10B01)资助

摘　　要：2008年汶川MS8.0强震中频繁出现断层穿越的地震滑坡,除发震断层的地震特性外,其自身场地效应也会影响斜坡动力响应,甚至加剧斜坡失稳.本文以汶川极震区绵竹九龙镇山前斜坡为典型实例,根据余震作用下斜坡不同高程实测地震记录及地脉动测试结果,通过单点谱比法（H/V）,获得斜坡地震动加速度随高程的放大系数和地脉动的频谱特征曲线,通过曲线对比分析发现1）斜坡两次典型余震PGA放大系数随高程先减小后增大,呈明显的“凹形”特征,“凹形”部位位于断层位置,其PGA放大系数约为斜坡底部测点0.4～1.0,坡顶测点的PGA放大系数则达到1.0～2.0倍.由于PGA放大系数是在断层位置出现的明显拐点,从地质上表明了断层场地效应明显;（2）各点NS/UD谱比普遍大于EW/UD谱比.断裂区域卓越频率为低频1Hz,小于其他测点的频率,对应谱比最大值高达3.0～4.0,高于其他测点谱比最大值.说明地表破裂处岩土体松散破碎,导致断层处的卓越频率较低,近场余震传播过来的高频地震波被断层隔断,地震加速度放大系数在该处发生了衰减,场地效应显著.本研究有助于增强断层场地对斜坡动力响应影响的认识.There are many landslides passed by faults. They are results from Wenchuan Ms 8. 0 earthquake in2008. Besides the movement of the seismogenic fault,its site effect can also influence the slope dynamic response and increase the slope instability. In this paper,the microtremors and seismic observations are performed along the front slope surface in Mianzhu Jiulong town. It uses the spectral ratio of horizontal to vertical components( H / V) of microtremor data and PGA amplification factors of acceleration records of two typical aftershocks,and obtains the spectral characteristic curves. By comparative analysis of the curves,it is found that: 1) with the growth ofelevation,the values of PGA amplification factors decrease at first,and then increase,presenting a ‘concave'shape. The concave-shape curves appear at the monitoring point around the fault zone. The values of PGA amplification factors can just reach to 0. 4 ~ 1. 0,while the values of PGA amplification factors at the monitoring point around the upper slope can even get to be 1. 0 ~ 2. 0. As the turning points appear around the fault zone,it shows the site effects of the fault from the geological view. 2) The NS / UD spectral ratio is generally greater than the EW / UD spectral ratio. The predominant frequency around the fault zone is near to the low frequency of 1Hz,smaller than any other monitoring point. It has the biggest spectral ratio of 3. 0 ~ 4. 0. It tells that the soil and rock of the surface rupture is loose and broken after the Wenchuan main shock. So the predominant frequency of the fault zone is low. The high frequencies of near-field aftershocks are filtered by the fault materials. Then the earthquake acceleration amplification coefficients are reduced as well. This study is helpful to enhance the understanding of the impact of the fault site effect on slope dynamic response.

关 键 词：断层穿越斜坡 放大效应 卓越频率 地震滑坡 

分 类 号：P642.22[天文地球—工程地质学]