利用背景噪声研究紫坪铺水库地区蓄水前后地壳介质波速变化

发布时间：2018-04-24 00:10

本文选题：背景噪声 + 紫坪铺水库　；参考：《中国地震局地震预测研究所》2015年硕士论文

【摘要】：中国是世界上水库数量最多的国家。水库在发挥重要作用的同时,也引发了一系列的地质灾害问题。中国又是世界上水库地震多发的国家之一。水库诱发地震不仅可能直接破坏水库大坝,还有可能引发严重的次生灾害。尤其是近些年,我国在地震多发的川滇地区建设了大量高坝、大库容的梯级电站。水库地震时有发生,大型水库的水库地震问题引起了地震学者的高度重视。汶川地震后,由于紫坪铺水库的特殊时空关系,更是引发广泛关注。本文利用2005年1月1日至2008年1月1日紫坪铺台网及YZP台连续波形资料,对紫坪铺水库库区地下介质展开研究。研究时间段包含了紫坪铺三次大规模蓄水和两次泄水的过程。具体研究方法为:利用地震背景噪声互相关提取台站对间经验格林函数(CCFs);经过较长时间的叠加获得参考格林函数(REF);通过比较经验格林函数(CCFs)与参考格林函数(REF)来测定介质相对波速的变化。根据得出的结果,本文分别对三次蓄水及两次泄水过程进行了分析,讨论了不同阶段影响相对波速变化的主要因素,追踪了水在不同深度介质中的渗透过程。同时,本文还分别对库区地下介质相对波速变化与库区地震频度、深度的关系进行了分析。主要研究结论如下:1、紫坪铺水库在大规模蓄水前,库区地下介质的相对波速变化与水位变化没有明显的相关性,而在后面的水位加卸载过程中,表现出了明显的负相关性,即水位升高,相对波速降低,水位降低,相对波速升高。分析认为,第一次蓄水及泄水时,压力是导致介质相对波速变化的主要因素,而渗透作用只影响到了2km以内的浅层介质。后两次蓄水及泄水时,渗透作用与压力共同作用。在第二次蓄水至最高点时,渗透作用影响至4km左右的断层,在第二次泄水至最低点时,渗透作用已影响至8km左右的断层。最后一次蓄水时,三个周期的相对波速变化都与水位变化非常的一致,具有较高的互相关系数。此时水已渗透至深度为8km以下的断层。2、通过库区地下介质相对波速变化与库区地震频度变化的关系分析,认为在三个水位快速上升的月份,对应着地震频次的相应增加,而同时对应着介质相对波速由0附近迅速降低的过程。3、通过库区地下介质相对波速变化与库区地震深度变化的关系分析,认为蓄水后大部分小震震源深度都明显集中在5km左右,这与本文分析的渗透作用过程相一致。本文的研究结论有利于深化对库区地下结构、状态和动力学过程的认识。同时,结合水库地震频次及深度的分析发现,对于地下浅层介质相对波速连续变化的研究,可能为水库诱发地震的判断及预测提供帮助,具有十分重要的意义。
[Abstract]:China has the largest number of reservoirs in the world. Reservoir plays an important role, but also triggered a series of geological disasters. China is also one of the countries in the world prone to reservoir earthquakes. Reservoir induced earthquakes may not only directly destroy reservoir dams, but also cause serious secondary disasters. Especially in recent years, a large number of cascaded hydropower stations with high dams and large reservoirs have been built in the earthquake-prone Sichuan-Yunnan region. Reservoir earthquakes occur from time to time, and earthquake problems in large reservoirs have attracted great attention of seismologists. After the Wenchuan earthquake, due to the special time-space relationship of Zipingpu reservoir, it aroused widespread concern. Based on the continuous waveform data of Zipingpu network and YZP station from January 1, 2005 to January 1, 2008, the underground media of Zipingpu reservoir area are studied. The research period includes three large-scale water storage and two drainage processes in Zipingpu. The specific research methods are as follows: the cross-correlation of seismic background noise is used to extract the empirical Green's function between stations and stations; the reference Green's function is obtained after a long period of superposition; and by comparing the empirical Green's function with the reference Green's function, the reference Green's function is obtained by comparing the empirical Green's function (CCFs) with the reference Green's function (REFF). The variation of the relative wave velocity of the medium was measured. According to the results obtained, the three water storage and two discharge processes are analyzed, and the main factors affecting the relative wave velocity at different stages are discussed, and the permeation process of water in different depth medium is tracked. At the same time, the relationship between the variation of relative wave velocity of underground media and seismic frequency and depth in the reservoir area is also analyzed in this paper. The main conclusions are as follows: before the large-scale storage of water in Zipingpu Reservoir, there is no obvious correlation between the variation of relative wave velocity and the change of water level in the underground media in the reservoir area, but in the process of loading and unloading of the later water level, there is an obvious negative correlation. That is, the water level rises, the relative wave velocity decreases, the water level decreases, and the relative wave velocity increases. It is concluded that the pressure is the main factor leading to the variation of the relative wave velocity of the medium during the first water storage and discharge while the permeation only affects the shallow media within the 2km. In the latter two times of water storage and drainage, osmotic action and pressure act together. At the second water storage to the highest point, the permeability affects the fault around 4km, and at the second discharge to the lowest point, the permeability affects the fault around 8km. At the last impoundment, the variation of relative wave velocity in the three periods is very consistent with the change of water level, and has a high correlation number. At this time, the water has penetrated to the fault below the depth of 8km. Through the analysis of the relation between the relative wave velocity change of underground media and the seismic frequency change in the reservoir area, it is concluded that the corresponding increase of earthquake frequency is corresponding to the three months when the water level rises rapidly. At the same time, corresponding to the process that the relative wave velocity of the medium decreases rapidly from 0 to 0, through the analysis of the relationship between the variation of the relative wave velocity of the underground medium in the reservoir area and the variation of the seismic depth in the reservoir area, it is considered that most of the focal depths of the small earthquakes after the storage of water are obviously concentrated around 5km. This is consistent with the osmotic process analyzed in this paper. The conclusion of this paper is helpful to deepen the understanding of underground structure, state and dynamic process of reservoir area. At the same time, combined with the analysis of seismic frequency and depth of reservoir, it is found that the study on the continuous variation of relative wave velocity in shallow underground media may be of great significance for the judgment and prediction of reservoir induced earthquakes.
【学位授予单位】：中国地震局地震预测研究所
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P315.728

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