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

Author(s):: 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

摘要:: 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。

Abstract:: 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.