贵州北盘江董箐水库邻区微地震精确定位及形成机制研究

发布时间：2018-10-12 18:29

【摘要】：董箐水库位于贵州省镇宁县与贞丰县的交界处,于2009年8月开始蓄水。北盘江地震台网在董箐水库蓄水后记录到了大量微地震,台网采用的快速地震定位算法精度不高,而要深入研究库区的地震活动、精细结构等需要更精确的定位结果。因此,本文采用定位精度更高的双差定位法对记录到的地震进行重新定位,精确的地震定位结果可以为库区地震活动规律提供更详细的信息,并可以为认识董箐水库诱发地震形成机制提供更多地球物理学依据。首先,利用双差定位法对2010年2月1日至2016年12月31日发生在董箐库区监测区(105.4°-106.0°E,25.2°-25.7°N)的2626次地震事件进行重新定位,得到2144次事件的精确定位结果。重定位后均方根残差(RMSCT)由0.2126s降低至0.0723s,东西、南北、垂向平均定位误差分别为184.5m,208.5m,303.5m,定位结果得到良好改善。其次,基于定位结果,对董箐水库区域地震活动性进行分析。结果显示,董箐水库在2009年8月开始蓄水之后,地震活动性增强。董箐库区在2010年2月至2015年11月间地震频次总体呈减少趋势,地震活动性减弱。该时间段库区进入应变积累期。董箐库区于2015年底地震活动性突然增强,这可能是由于库区应变积累达到较高水平后释放应变能导致的。再次,根据董箐库区地震活动规律,对库区地震活动做了时空演化特征分析。结果表明,董箐水库在蓄水初期(2010年2月1日至2010年9月30日),水库大坝东侧和东北侧出现大量地震,且震源深度较浅,与蓄水过程有较强响应关系。随着蓄水时间推移,地震有往大坝南侧的坝草断裂迁移的现象。并且,随着蓄水时间的推移,地震有往距大坝更远和更深处迁移的现象。最后,根据董箐库区地震活动时空演化特征并结合库区构造环境、岩石岩性和水位变化规律等,对董箐水库区为地震形成机制进行讨论。在蓄水初期,诱发地震的主要因素是库水荷载;蓄水位稳定后,诱发地震的主要因素是库水渗透引起的孔隙压力增加。根据这艾断裂附近地震丛集的震源深度分布,推测出了这艾断裂的倾向和倾角。
[Abstract]:Dongqing Reservoir, located at the junction of Zhenning County and Zhenfeng County, Guizhou Province, began to store water in August 2009. The Beipanjiang seismic network recorded a large number of micro-earthquakes after the Dongqing reservoir was impounded. The accuracy of the fast seismic location algorithm used in the network is not high, but more accurate location results are needed to deeply study seismic activities and fine structures in the reservoir area. Therefore, the double-difference positioning method with higher positioning accuracy is used to relocate the recorded earthquakes, and accurate seismic location results can provide more detailed information for the seismic activity law in the reservoir area. It can provide more geophysical basis for understanding the formation mechanism of Dongqing reservoir induced earthquake. First, 2626 seismic events occurred in Dongqing reservoir area (105.4 掳-106.0 掳EN 25.2 掳-25.7 掳N) from February 1, 2010 to December 31, 2016 were relocated by using the double difference location method, and the exact location results of 2144 events were obtained. The root mean square residuals (RMSCT) were reduced from 0.2126s to 0.0723s after repositioning. The average positioning errors in east-west, north-south, and north-south were 184.5 mg, 208.5 m-1 and 303.5 m, respectively, and the positioning results were well improved. Secondly, based on the location results, the regional seismicity of Dongqing reservoir is analyzed. The results showed that the seismic activity increased after Dongqing reservoir began to store water in August 2009. From February 2010 to November 2015, the frequency of earthquakes in Dongqing reservoir area decreased and the seismicity weakened. In this period, the reservoir area entered the period of strain accumulation. The seismic activity in Dongqing reservoir area suddenly increased at the end of 2015, which may be due to the release of strain energy after strain accumulation reached a high level in the reservoir area. Thirdly, according to the regularity of seismic activity in Dongqing reservoir area, the temporal and spatial evolution characteristics of seismic activity in the reservoir area are analyzed. The results show that a large number of earthquakes occurred on the east and northeast side of the dam in the early stage of Dongqing reservoir's water storage (from February 1, 2010 to September 30, 2010), and the focal depth is relatively shallow, which has a strong response relationship with the water storage process. As the storage time goes on, the earthquake migrates to the south of the dam. Moreover, as the storage time goes on, the earthquake migrates farther and deeper from the dam. Finally, according to the spatial and temporal evolution characteristics of seismic activities in Dongqing reservoir area and the structural environment, lithology and water level variation law of the reservoir area, the mechanism of earthquake formation in Dongqing reservoir area is discussed. In the early stage of water storage, the main factor of inducing earthquake is reservoir water load, and the main factor of inducing earthquake is the increase of pore pressure caused by reservoir water permeation after the reservoir water level is stabilized. Based on the focal depth distribution of the earthquake cluster near the Ai fault, the tendency and inclination of the fault are inferred.
【学位授予单位】：成都理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：P315.728;TV697.24

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