三峡大坝蓄排水过程对岩石各向异性的动态影响研究

The safety of rocks of Three Gorges Dam has been being concerned by earthquake engineering geologists. The time-varying features of the rock anisotropy correspond to the alternations of surrounding stress fields. The accumulation and release of the stress refer to the processes of reservoir water storage and drainage. In order to evaluate the time-varying effects of the reservoir water storage and drainage on the anisotropy of Three-Gorges host rocks, the present study calculates the anisotropic parameters of the host rocks, based on the massive historical seismic records, and then studies the relations in between the two factors. By selecting the wave phases of the seismic events happened in the reservoir area and surrounding areas, surface waves are purified to abstract the high-resolution dispersion data. Several anisotropic models are optimized prefer to effective rock model. The stable surface-wave velocities and the perturbations are inverted to get the anisotropic parameters of the host rocks, which are used to evaluate the changes in physical properties.

三峡大坝的岩体安全性一直是地震地质工程关注的热点问题，三峡核心地区岩体的各向异性及其时变特征反映了所承受的地应力变化，地应力的积累和释放过程伴随着大坝的蓄排水动态过程。为了获得大坝蓄排水过程对三峡岩体各向异性的影响，本项目基于三峡地震台网监测到的大量历史地震数据，提炼岩石各向异性参数及其时变效应，进行相关分析。主要是利用发生在库区及周边地区的地震事件，提取高分辨率的时变面波频散信息，选择各向异性等效模型，通过地震波的背景速度及扰动量协同反演各向异性参数，进而研判岩石的物理性质变化。

作为目前世界上规模最大的水利枢纽工程，三峡大坝的安全性一直是国际社会尤其是地震地质学者关注的热点问题。本课题通过研究三峡大坝的蓄排水动态水位与地下岩体的各向异性变化的对应关系，探讨大坝蓄排水过程对岩石各向异性的动态影响。通过分析三峡地区地震台站波形数据，提取高分辨率的时变面波频散。面波层析成像的研究结果显示三峡库区地壳部分整体上属于低速异常区，各向异性特征十分明显。低速异常和各向异性表明此区域存在大量裂隙，三峡库区的蓄排水有利于区域地壳浅部物质的调整，这是三峡大坝蓄排水过程对岩石各向异性、地震活动性产生重要影响的根本原因。通过研究三峡地区b值空间分布特征，发现三峡地区b值介于0.6~1.6之间，表明该地区地震活动强度低于长江流域其他地区，但地震发生频度较高。基于三峡坝区秭归站的历史降雨数据进行趋势分析，发现三峡大坝蓄水过程对库区降雨具有小尺度的影响；相伴的重力效应会诱发微小地震和引起垂向形变。本课题通过加密完成了三重观测网，包括区域观测网、三峡库区网和流动地震台网，为后续研究提供良好的数据基础。