长周期地脉动观测在西安地区地下构造调查中的应用

Application of Long Period Microtremor Observation on Underground Structure Investigation in Xi'an Area

通过对西安两个区域(西安交通大学校园、市区东西与南北轴线)进行长周期地脉动观测、数据采集与分析,得到西安地区地下构造固有频率特性,进而推断出观测区地下软土层厚度分布趋势。经过对数据进行Nakamura法处理可以清晰看出:地基土层起着滤波器作用,有选择地滤掉某些成分,放大了某些频谱成分,使谱型局部受到改造;不同场地土质对地脉动的响应具有频率依赖性以及频率选择效应。同时探明观测区长周期地脉动的空间变化规律,了解了沉积层厚度以及横向变化规律,可为西安地区工程抗震提供参考依据。

Through carrying on long period microtremor observation,data acquisition and analysis in two regions（Xi＇an Jiaotong University campus,the urban east-west and north-south axis）of Xi＇an area,the natural frequency characteristic of underground structure in Xi＇an area is obtained,and the distributing tendency of thickness of soft soil is infered.After data treatment using Nakamura method,it is clearly showed that the role of the foundation soil like a filter which selectively filtrats out certain components,amplifies some spectrum components,and causes transformation of the local spectrum shape. In different locations soil texture has the frequency dependence as well as the frequency selection effect when response microtremor.Simultaneously verifying the spatial variation of microtremor,the thickness of sedimentary layers and its lateral variation rule in the surving area are understanded.The result provides the reference for project resistance.