地震研究

宁夏及邻区异常低视应力“地震事件”的发现及研究^*

曾宪伟,罗恒之,朱鹏涛,崔瑾

(宁夏回族自治区地震局,宁夏银川 750001)

关键词：视应力; 爆破事件; 波形互相关; 小波包分量比

Discovery and Research of “Earthquake Events” with Very Low Apparent Stress

ZENG Xianwei,LUO Hengzhi,ZHU Pengtao,CUI Jin

(Earthquake Agency of Ningxia Hui Autonomous Region,Yinchuan 750001,Ningxia,China)

Keywords：apparent stress; blasting events; waveform cross-correlation; spectral component ratio of wavelet-packet

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参考文献

计算宁夏及邻区一些中小“地震事件”视应力,发现与同震级事件相比,视应力成倍降低。结合这些异常事件的发生时刻和所在位置等,初步判定其为疑似爆破事件。进一步利用P波初动方向、波形互相关特征和不同频带能量比值等方法,发现异常事件P波垂直向初动均向上,同一台站记录的同一区域的不同异常事件波形相关系数较大,异常事件波形低频信号比较发育,应该是爆破事件。

We calculate the apparent stress of moderate and small earthquakes in Ningxia area and find that the apparent stress values of some events decrease multiply relative to other events of the same magnitude. Combined with the occurrence time and epicenter of the events,we initially identified these abnormal events as doubtful blasting events. Then,by analyzing the P-wave initial moving direction,waveform cross-correlation and energy ratio of different frequency bands etc.,we find that these abnormal events have some common features,such as the vertical initial motion of P wave is upward,the correlation coefficients of waveforms in the same region recorded by the same station are larger,and the low frequency signals of waveforms are more developed. Basis on it,we confirm that these abnormal events should be blasting events.

引言
1 数据与方法
2 计算结果
3 异常事件分析与讨论
4 结论

表1 疑似爆破与地震事件目录<br/>Tab.1 Catalogue of suspected blasting and earthquakes

表1 疑似爆破与地震事件目录
Tab.1 Catalogue of suspected blasting and earthquakes

图1 疑似爆破、地震及矿区分布图(矿区影像图来自GoogleEarth)<br/>Fig.1 Distribution of suspected blasting events,earthquakes and mining area(images of mining area come from GoogleEarth)

图1 疑似爆破、地震及矿区分布图(矿区影像图来自GoogleEarth)
Fig.1 Distribution of suspected blasting events,earthquakes and mining area(images of mining area come from GoogleEarth)

图2 地震事件与疑似爆破的视应力对比图<br/>Fig.2 Comparison of apparent stress of suspected blasting events and earthquakes

图2 地震事件与疑似爆破的视应力对比图
Fig.2 Comparison of apparent stress of suspected blasting events and earthquakes

图3 相同震级的地震与疑似爆破的视应力平均值对比图<br/>Fig.3 Mean value of apparent stress of suspected blasting events and earthquakes with the same magnitude

图3 相同震级的地震与疑似爆破的视应力平均值对比图
Fig.3 Mean value of apparent stress of suspected blasting events and earthquakes with the same magnitude

图4 NSS台记录的疑似爆破(a)与地震事件(b)的垂直向原始波形及其相应降嗓波形(c,d)<br/>Fig.4 Vertical original waveforms of suspected blasting event(a)and earthquake(b)recorded by the NSS station and their corresponding noise reduction waveforms(c,d)

图4 NSS台记录的疑似爆破(a)与地震事件(b)的垂直向原始波形及其相应降嗓波形(c,d)
Fig.4 Vertical original waveforms of suspected blasting event(a)and earthquake(b)recorded by the NSS station and their corresponding noise reduction waveforms(c,d)

图5 三关口矿区4次疑似爆破事件(a)和3次疑似爆破事件(b)P波垂直向记录波形及其相关系数(c,d)<br/>Fig.5 Vertical waveforms of P wave of 4 suspected blasting events(a)and 3 suspected blasting events(b)and their correlation coefficients(c,d)in Sanguankou mining area

图5 三关口矿区4次疑似爆破事件(a)和3次疑似爆破事件(b)P波垂直向记录波形及其相关系数(c,d)
Fig.5 Vertical waveforms of P wave of 4 suspected blasting events(a)and 3 suspected blasting events(b)and their correlation coefficients(c,d)in Sanguankou mining area

图6 新井矿区3次疑似爆破事件P波垂直向记录波形(a)和带通滤波(3～4 Hz)后的波形(b)及其相关系数(c,d)<br/>Fig.6 Vertical waveforms of P wave of 3 suspected blasting events(a),waveforms after bandpass filtering(3 ～ 4 Hz)(b)and their correlation coefficient(c,d)in Xinjing mining area

图6 新井矿区3次疑似爆破事件P波垂直向记录波形(a)和带通滤波(3～4 Hz)后的波形(b)及其相关系数(c,d)
Fig.6 Vertical waveforms of P wave of 3 suspected blasting events(a),waveforms after bandpass filtering(3 ～ 4 Hz)(b)and their correlation coefficient(c,d)in Xinjing mining area

图7 地震事件和疑似爆破事件不同频带能量比值图[横轴i(i=1,2,3)与纵轴的Ei对应,代表3个不同的频带]<br/>Fig.7 Energy ratios of earthquakes and blasting events in different frequency bands(the horizontal axis i corresponds to vertical axis Ei(i=1,2,3)and represents 3 different frequency bands)

图7 地震事件和疑似爆破事件不同频带能量比值图[横轴i(i=1,2,3)与纵轴的Ei对应,代表3个不同的频带]
Fig.7 Energy ratios of earthquakes and blasting events in different frequency bands(the horizontal axis i corresponds to vertical axis Ei(i=1,2,3)and represents 3 different frequency bands)

图8 地震事件、落实爆破事件不同频带能量比值图(改绘自曾宪伟等(2008),横轴i同图 7)<br/>Fig.8 Energy ratio of earthquakes and blasting events in different frequency bands(modified from Zenget al,2008,the horizontal axis i is the same as that shown in Fig.7)

图8 地震事件、落实爆破事件不同频带能量比值图(改绘自曾宪伟等(2008),横轴i同图 7)
Fig.8 Energy ratio of earthquakes and blasting events in different frequency bands(modified from Zenget al,2008,the horizontal axis i is the same as that shown in Fig.7)