地震研究

利用背景噪声研究通海5.0级、墨江5.9级地震震源区波速变化

杨建文^1,2,叶泵^1,2,高琼^1,2,王军^1,2,陈佳^1,2

(1.中国地震科学实验场大理中心,云南大理671000; 2.云南大理滇西北地壳构造活动野外科学观测研究站,云南大理671000)

Study of the Wave Velocity Changes in the Focal Area of the Tonghai M_S5.0 Earthquake and the Mojiang M_S5.9 Earthquake by Ambient Noise

YANG Jianwen^1,2,YE Beng^1,2,GAO Qiong^1,2,WANG Jun^1,2,CHEN Jia^1,2

(1.Dali Center of China Earthquake Science Experimental Site,Dali 671000,Yunnan,China;2.Field Scientific Observation and Research Station on Crustal Tectonic Activities in Dali,Northwest Yunnan,Dali 671000,Yunnan,China)

Keywords：ambient noise; waveform cross-correlation; the empirical Green's function; wave velocity change

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参考文献

利用2017年1月31日—2019年12月1日云南数字地震台网的宽频带连续波形资料,基于背景噪声互相关方法,提取了14个台站对当天经验格林函数与参考经验格林函数的直达瑞利波走时偏移来研究2018年通海5.0级、墨江5.9级地震震源区的波速变化特征。结果表明,通海5.0级和墨江5.9级地震都在一定程度上造成了震源区地壳介质速度的变化。地震发生前后,穿过地震震中和震中附近的部分台站对的瑞利波走时偏移在地震发生前的20余天表现出明显的异常特征,且短期内走时变化具有较好的同步性,但异常幅度大小和异常持续时间存在一定差异,异常台站对走时偏移变化形态为“V”或双“V”型结构,两次地震都发生在了第1个“V”型的前端。多台站对组合的平均走时偏移结果显示,两次地震造成的震源区波速的异常持续时间大概都为260 d(通海地震略长于墨江地震),但墨江地震造成的最初的走时偏移变化量和持续时间均高于通海地震。

Based on the ambient noise cross-correlation method,we extract the travel time shift of the direct Rayleigh-wave of the daily empirical Green's function and the referential empirical Green's function of 14 station pairs to study the characteristics of the wave velocity changes in the source region of the Tonghai MS5.0 earthquake and the Mojiang MS5.9 earthquake by using continuous seismic data recorded by the broadband stations of the Yunnan Digital Seismic Network from January 2017 to December 2019.The results show that the seismic velocity are changed in the source region by the Tonghai MS5.0 earthquake and the Mojiang MS5.9 earthquake in 2018 to a certain extent.Before and after the two earthquakes,the travel time shift of the Rayleigh wave of the station pairs passing through the epicenters and their vicinity shows obvious abnormal characteristics about 20 days before the earthquakes,and the travel-time changes are synchronous in the short term but there are some differences between the amplitude and the lasting-time of the anomaly of the two earthquakes.The abnormal travel-time shift of the station pairs is V-shaped or double V-shaped,and both earthquakes occurred before the appearance of the first V-shape.The average travel-time shift of multi-station pairs show that the seismic velocity changes in the source region caused by the Tonghai MS5.0 and the Mojiang MS5.9 earthquakes both last about 260 days.The anomaly of the Tonghai earthquake last longer than the one of the Mojiang earthquake,but in the early stage the travel-time shift is more obvious and the lasting-time of the anomaly caused by the Mojiang earthquake is longer than those caused by the Tonghai earthquake.

引言
1 数据和方法
2 结果与分析
3 讨论
4 结论

图1 本文研究所用数字地震台站、地震震中及相关台站对分布<br/>Fig.1 Distribution of digital seismic stations,earthquake epicenters,and related station pairs

图1 本文研究所用数字地震台站、地震震中及相关台站对分布
Fig.1 Distribution of digital seismic stations,earthquake epicenters,and related station pairs

图2 YUJ-JIG、YUJ-SIM台站对的原始(a)和对称叠加后的(b)经验格林函数(3年数据叠加结果)<br/>Fig.2 The original(a)and the symmetric superposition(b)of YUJ-JIG,YUJ-SIM station pairs of the empirical Green's function(overlay of 3 years' data)

图2 YUJ-JIG、YUJ-SIM台站对的原始(a)和对称叠加后的(b)经验格林函数(3年数据叠加结果)
Fig.2 The original(a)and the symmetric superposition(b)of YUJ-JIG,YUJ-SIM station pairs of the empirical Green's function(overlay of 3 years' data)

图3 参考经验格林函数的台站对间距-时间图<br/>Fig.3 Station pair distance-time diagram of the referential empirical Green's function

图3 参考经验格林函数的台站对间距-时间图
Fig.3 Station pair distance-time diagram of the referential empirical Green's function

图4 YUJ-SIM台站对当天经验格林函数与参考经验格林函数互相关计算结果<br/>Fig.4 The cross-correlation calculation results of the daily empirical Green's function and the referential empirical Green's function of YUJ-SIM station pair

图4 YUJ-SIM台站对当天经验格林函数与参考经验格林函数互相关计算结果
Fig.4 The cross-correlation calculation results of the daily empirical Green's function and the referential empirical Green's function of YUJ-SIM station pair

图5 YUJ-SIM台站对瑞利波走时偏移变化曲线<br/>Fig.5 Curve of the travel-time shift of the Rayleigh wave of YUJ-SIM station pair

图5 YUJ-SIM台站对瑞利波走时偏移变化曲线
Fig.5 Curve of the travel-time shift of the Rayleigh wave of YUJ-SIM station pair

图6 部分台站对瑞利波走时偏移变化曲线<br/>Fig.6 Curves of the travel-time shift of the Rayleigh wave of some station pairs

图6 部分台站对瑞利波走时偏移变化曲线
Fig.6 Curves of the travel-time shift of the Rayleigh wave of some station pairs

图7 TOH-YIM(a)和YIM-JIS(b)台站对瑞利波走时偏移变化曲线<br/>Fig.7 Curves of the travel-time shift of the Rayleigh wave of TOH-YIM station pair(a)and YIM-JIS station pair(b)

图7 TOH-YIM(a)和YIM-JIS(b)台站对瑞利波走时偏移变化曲线
Fig.7 Curves of the travel-time shift of the Rayleigh wave of TOH-YIM station pair(a)and YIM-JIS station pair(b)

图8 YUJ-SIM(a)和JIS-SIM(b)台站对瑞利波走时偏移变化曲线<br/>Fig.8 Shift of the travel-time of the Rayleigh wave of YUJ-SIM(a)and JIS-SIM(b)station pair

图8 YUJ-SIM(a)和JIS-SIM(b)台站对瑞利波走时偏移变化曲线
Fig.8 Shift of the travel-time of the Rayleigh wave of YUJ-SIM(a)and JIS-SIM(b)station pair

图9 通海5.0级(a)和墨江5.9级(b)地震震源区瑞利波走时偏移<br/>Fig.9 Shift of the travel-time of the Rayleigh wave in the source area of the Tonghai MS5.0 earthquake(a)and the Mojiang MS5.9 earthquake(b)

图9 通海5.0级(a)和墨江5.9级(b)地震震源区瑞利波走时偏移
Fig.9 Shift of the travel-time of the Rayleigh wave in the source area of the Tonghai MS5.0 earthquake(a)and the Mojiang MS5.9 earthquake(b)

表1 两次地震前后台站对瑞利波走时偏移变化<br/>Tab.1 Shift of the travel-time of the Rayleigh wave of the stations pairs before and after the two earthquakes

表1 两次地震前后台站对瑞利波走时偏移变化
Tab.1 Shift of the travel-time of the Rayleigh wave of the stations pairs before and after the two earthquakes

图10 通海5.0级地震附近5个台站对(a)和墨江5.9级地震附近4个台站对(b)组合平均走时偏移<br/>Fig.10 The average travel-time shifts of the combination of 5 station-pairs near the epicenter of the Tonghai MS5.0 earthquake(a)and the combination of 4 station-pairs near the epicenter of the Mojiang MS5.9 earthquake(b)

图10 通海5.0级地震附近5个台站对(a)和墨江5.9级地震附近4个台站对(b)组合平均走时偏移
Fig.10 The average travel-time shifts of the combination of 5 station-pairs near the epicenter of the Tonghai MS5.0 earthquake(a)and the combination of 4 station-pairs near the epicenter of the Mojiang MS5.9 earthquake(b)