地震研究

利用2018年8月13日至12月31日云南通海MS5.0震群震源区的观测报告,采用双差层析成像方法对通海MS5.0震群序列重定位,获得了震源区附近上地壳的三维速度结构。结果表明:震源区速度结构呈现明显横向不均匀,在玉江断裂和小江断裂南段的明星—二街断裂交汇处,5 km深度上,震源区出现高速异常,延伸至10 km,而在15 km深度上,表现为低速异常。重定位后的震源位置精度明显得到提高,地震事件分布更加集中,震中位置呈NE—SW向条带状分布,2次主震空间相距约18 km,震源深度分布范围为3 ～ 12 km,8月13,14日2次MS5.0地震的震源深度分别约为8.63 km,和9.16 km。综合分析震源区地震地质资料、速度结构成像结果及重定位后地震序列空间分布认为,位于小江断裂带南段,且与明星—二街断裂近乎平行的隐伏断裂可能是此次通海震群的发震构造。

In this study,we relocated the 2018 Yunnan Tonghai MS5.0 earthquakes swarm and determined a 3D velocity model of the upper crust of source area using the double-difference seismic tomography method.All the seismic phase observation reports are provided by the China Earthquake Networks Center(CENC).The results show that the velocity structure of the epicenters of the Tonghai sequence present obvious lateral inhomogeneity.At the junction of the Yujiang fault and the Mingxing-erjie fault which was located in the south of Xiaojiang fault,and the velocity presents high values at the depth 5 km and till to the 10 km,while the velocity presents low values at the depth of 15 km.The well relocated epicenters of the Tonghai MS5.0 earthquakes sequence exhibited in a narrow band along the NE-SE direction,the distance between two main events is approximately 18 km,and the predominant range of depth distribution is from 3 km to 12 km.The depths of the two main events occurred on 13 and 14 August are 8.63 km and 9.16 km,respectively.Based on the comprehensive results of the velocity structure of source area,the distribution of the relocated epicenters and hypocenters,and the geological structures,we infer that a pre-exist fault which is parallel to the Mingxing-erjie fault is the seismogenic fault of the Tonghai MS5.0 seismic swarm.

引言
1 研究区概况
2 研究方法与数据选取
3 计算结果
4 讨论
5 结论

图1 研究区域断裂和台站分布(a),区域断裂及地震分布(b)<br/>Fig.1 Geologic structure background and distribution of stations in the study area(a),regional geologic structure background and distribution of earthquakes(b)

图1 研究区域断裂和台站分布(a),区域断裂及地震分布(b)
Fig.1 Geologic structure background and distribution of stations in the study area(a),regional geologic structure background and distribution of earthquakes(b)

表1 通海2次MS5.0地震震源机制解<br/>Tab.1 Focal mechanism of the two Tonghai MS5.0 mainshocks

表1 通海2次MS5.0地震震源机制解
Tab.1 Focal mechanism of the two Tonghai MS5.0 mainshocks

图2 筛选前(a)和筛选后(b)数据的走时曲线拟合图<br/>Fig.2 The diagram for fitting travel time with epicentral distance(a)before and(b)after selection

图2 筛选前(a)和筛选后(b)数据的走时曲线拟合图
Fig.2 The diagram for fitting travel time with epicentral distance(a)before and(b)after selection

表2 通海震源区附近速度模型<br/>Tab.2 Velocity model of the Tonghai earthquake region

表2 通海震源区附近速度模型
Tab.2 Velocity model of the Tonghai earthquake region

图3 利用L曲线法所选的最优平滑因子(a)和阻尼参数(b)<br/>Fig.3 The optimum smoothing parameter(a)and damping parameter(b)selected by the L curve method

图3 利用L曲线法所选的最优平滑因子(a)和阻尼参数(b)
Fig.3 The optimum smoothing parameter(a)and damping parameter(b)selected by the L curve method

图4 不同深度剖面的棋盘模型测试结果<br/>Fig.4 The checkerboard resolution test at different depths

图4 不同深度剖面的棋盘模型测试结果
Fig.4 The checkerboard resolution test at different depths

图5 不同深度P波速度、S波速度和2018年8月13日至12月31日ML≥0.0地震分布(黑色圆点)<br/>Fig.5 P-wave velocity distribution,S-wave velocity distribution,and ML≥0.0 earthquakes distribution from Aug.13 to Dec.31,2018(black points)at different depths

图5 不同深度P波速度、S波速度和2018年8月13日至12月31日ML≥0.0地震分布(黑色圆点)
Fig.5 P-wave velocity distribution,S-wave velocity distribution,and ML≥0.0 earthquakes distribution from Aug.13 to Dec.31,2018(black points)at different depths

图6 2018-08-13—2018-12-31 ML≥0.0地震重定位前(a),后(b)走时残差分布和震源深度分布(c)<br/>Fig.6 The arrival time residual distribution before(a)and after(b)event relocation of ML≥0.0 from Aug.13 to Dec.31,2018,and the distribution of earthquake depth(c)

图6 2018-08-13—2018-12-31 ML≥0.0地震重定位前(a),后(b)走时残差分布和震源深度分布(c)
Fig.6 The arrival time residual distribution before(a)and after(b)event relocation of ML≥0.0 from Aug.13 to Dec.31,2018,and the distribution of earthquake depth(c)

图7 2018-08-13—2018-08-31研究区域内ML≥0.0地震的初始定位结果(a)、重定位结果(b)、重定位后地震震源深度随时间变化图(c)、沿AA'(d)和沿BB'剖面(e)地震分布图<br/>Fig.7 Initial(a)and relocation(b)results ot epicenter distribution of ML≥0.0 earthquakes from Aug.13 to Aug.31,2018 results; the relocated earthquake depth changes with time(c); P wave velocity along the AA' section(d)and BB' section

图7 2018-08-13—2018-08-31研究区域内ML≥0.0地震的初始定位结果(a)、重定位结果(b)、重定位后地震震源深度随时间变化图(c)、沿AA'(d)和沿BB'剖面(e)地震分布图
Fig.7 Initial(a)and relocation(b)results ot epicenter distribution of ML≥0.0 earthquakes from Aug.13 to Aug.31,2018 results; the relocated earthquake depth changes with time(c); P wave velocity along the AA' section(d)and BB' section

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备注

引言

1 研究区概况

2 研究方法与数据选取

3 计算结果

4 讨论

5 结论

期刊信息