Application of Double-difference Relocation Method Combined with Waveforms Cross-correlation on Earthquakes in the Three Gorges Reservoir Area
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摘要: 本文采用基于波形互相关算法的双差定位方法对三峡水库地震进行精定位和地震活动性分析。首先使用双谱互相关方法分析了三峡库区加密台网于2009年3月至2010年12月观测到的地震波形数据，并对波形互相关分析的结果进行了评价。基于结合获得的波形互相关数据使用双差定位方法对地震事件进行精定位研究，结果表明使用双谱法验证的波形互相关数据的定位精度要高于其他数据的结果，其东西向震源位置平均误差为3.2m、南北向为3.9m、垂直向为6.2m。重定位震中结果显示巴东神龙溪两岸微震分布明显呈现出3条近东西向的线性条带状，与地表小规模断裂和碳酸盐岩地层走向一致，揭示了库水主要沿着溶洞或者地下暗河渗透进而诱发地震活动，较强地震可能是微小地震贯穿活动面的结果。Abstract: In this paper, we applied the double difference location method based on waveform cross-correlation algorithm for earthquake precision positioning of the Three Gorges Reservoir (TGR). First we used bispectrum cross-correlation method to analyze the seismic waveform data of TGR encrypted networks in March 2009 to December 2010, and evaluate the quality of waveform cross-correlation analysis. Combining the waveform cross-correlation of data obtained, we used the double difference method to relocate the position of quakes. The results show that the location by using bispectrum verified waveform cross-correlation data is higher than other type of data, and the mean 2sig-errors in EW, NS and UD are 3.2m, 3.9m and 6.2m, respectively. The results also show that the Badong and Shenlong River quake in reservoir distribution is characterized by linear distribution of three nearly east-west, which is in accordance with the small faults and carbonate strata line of new tectonic period, revealing reservoir water main along the underground river or cave penetration induced seismic activity. A strong earthquake may be the result of a small earthquakes that broken through the active plane.
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图 2 地震事件对在台站DTP（a）、LPT（b）的波形互相关示意图
黑色波形为事件242波形，红色为244波形，前两行中的P表示该台站地震目录P波走时，第三行中的CC为波形互相关系数，tdt为波形互相关P波到时差，tdiff为地震目录P波到时差
Figure 2. Waveforms showing correlation of event pair #1 from station DTP (a) and LPT (b)
图 3 三峡库区2种互相关系数评估柱状统计图
（a）P波传统互相分析结果统计图，纵坐标括号内数值为互相关记录条数，互相关系数统计间隔为0.01；（b）P波双谱验证互相关分析结果统计图，纵坐标括号内的第一个数值为互相关系数大于0.7的记录个数，第二个为总记录个数，3条竖线表示了CClim (l)=0.5，CClim=0.7，CClim (u)=0.9；（c）S波传统互相关分析结果统计，其余同图（a）；（d）S波双谱验证互相关分析结果统计图，其余同图（b）
Figure 3. Histogram of two kinds of cross-correlation coefficients in the Three Gorges Reservoir Area
图 4 三峡库区地震目录的震源距离统计图
Figure 4. Plot of total number of event pairs and separation distance of hypocenters
图 5 台站地震对和震相互相关系数分布图
（a）P波数据分布图；（b）P波互相关系数与震源距密度分布图，横坐标为各个台站记录到的同一地震对的震源距离，纵坐标为相应地震对的互相关系数，其中密度统计图统计间隔震源距为2km，互相关系数为0.1；（c）和（d）为S波分布图，其余同（a）和（b）。密度为对应矩形色块内的数据量与总数据量的比值，衡量的是色块内数据占总数据的比重，无量纲。
Figure 5. Distribution of event pairs and cross-correlation coefficient for all stations
图 6 地震走时曲线和和达曲线图
（a）为最小二乘剔除误差较大震相后走时曲线；（b）为初始震相走时曲线；（c）为剔除误差较大震相后的TS-TP曲线，红线为直线拟合结果vP/vS为1.73；（d）为初始Ts-Tp曲线
Figure 6. The travel time curves and Wadati plot
图 7 5244个地震事件的初始震中分布图、深度剖面图和统计图
（a）地震事件初始震中分布图；（b）震源深度沿着纬度方向的剖面图；（c）震源深度沿经度方向的剖面图；（d）震源深度统计图
Figure 7. Plots of distribution of space, depth and statistical results of 5244 seismic events
图 8 不同数据类型的hypoDD定位结果
（a）初始地震事件震中分布；（b）仅地震目录数据的hypoDD定位结果；（c）结合传统互相关分析与地震目录数据的hypoDD定位结果；（d）结合双谱验证互相关分析与地震目录数据的hypoDD定位结果。左上角数字为使用不同数据时获得的重定位地震事件数
Figure 8. Map view of relocation results from different type data by HypoDD
图 9 不同数据类型的hypoDD定位结果的深度和RMS分布图
（a）仅使用地震目录数据；（b）结合传统互相关分析与地震目录数据；（c）双谱法互相关分析与地震目录数据hypoDD定位结果，上图为经度方向的深度分布图，下图为经度方向的误差分布图
Figure 9. The distribution of depth and RMS from different data by hypoDD relocation
图 10 不同数据类型的双差定位结果误差统计
（a）—（c）为地震目录定位结果，（d）—（f）为结合传统互相关分析和地震目录定位结果，（g）—（i）为结合双谱验证波形互相关和地震目录定位结果
Figure 10. The histograms of statistical errors of different type data by hypoDD relocation
事件对242；244 2009-03-25 22：16：21.3 ML1.3；2009-03-25 22：17：17.3 ML 1.5 台站 互相关延时/s 互相关系数 震相 台站 互相关延时/s 互相关系数 震相 BJH -0.033 0.9852 P JJP -0.035 0.986 P CJP -0.03 0.9733 P LPT -0.023 0.9912 P DJW -0.016 0.9848 P BJH -0.04 0.9876 S DPC -0.015 0.9813 P CJP -0.039 0.9635 S DTP -0.029 0.952 P DJW -0.009 0.9976 S FJP -0.027 0.9887 P GJY -0.04 0.9719 S GJY -0.033 0.984 P LPT -0.015 0.9132 S 
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