利用背景噪声研究紫坪铺水库水位加卸载对库区地下介质波速的影响

Using ambient noise to study the seismic velocity changes caused by the rise and fall of the water level in the Zipingpu reservoir region

摘要:

基于2005年1月1日～2008年1月1日紫坪铺台网及YZP台连续波形资料，利用噪声互相关技术研究了紫坪铺水库区域在蓄水、泄水过程中库区介质的变化特征，同时对可能的渗透过程进行了讨论。使用移动窗口互谱方法计算了库区台站对之间的相对波速变化。结果表明，在紫坪铺水库的3次大规模蓄水及2次泄水过程中，地下介质相对波速变化与水位变化之间存在较为明显的相关性，且在时间上有一定延迟，其可能与水的渗透有关。分析认为蓄水对浅层介质产生的作用最快，影响最大，波速的变化是蓄水产生的压力及渗透共同作用的结果。在第1次蓄水时，压力起主要作用，后2次蓄水时，渗透起主要作用，且渗透作用已影响至深达8km左右的断层。

Abstract:

The feature of media changes beneath the Zipingpu reservoir has been studied and the process of permeation with the the water level rise and fall of the reservoir from January 2005 to January 2008 for ambient noise cross correlation by using continuous seismic data recorded by the stations of Zipingpu seismic network and YZP station has been discussed. A moving-window cross-spectrum technique has been used to calculate the seismic velocity changes between station pairs. Results revealed that there is an obvious relationship between seismic velocity and the water level changes with a time delay that may be caused by permeation during three main impoundments and two large scale disemboguements. Impoundment generates a fast and large impact on the superficial layer，and the changes of seismic velocity is the result of increased pressure and permeation during the impoundment. At the first impoundment，the main effect factor is the pressure. Then，during the next two process of impoundment，permeation becomes the main effect factor and has affected the fault in the depth of about 8km.