一种低频地震事件的检测方法——在汶川地震芦山地震前的初步应用
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摘要
本文发展了一种单台检测低频地震事件的方法,并用其检测2008年汶川MS8.0地震、2013年芦山MS7.0地震震前的低频事件。使用汶川地震芦山地震前周边的宽频带台站数月的垂直向连续波形,经过2~8 Hz带通滤波、窗长为10s的包络平滑、窗长为20min的中值滤波,去除近场天然地震及远场大震与低频噪声的影响后,发现这两个大地震前有少数台站在连续数天的时间内,出现持续时间长(数十分钟到数小时)、包络中值明显大于背景噪声的现象,其波形记录及包络特征与非火山震颤(NVT)的波形记录及包络特征具有较好的相似性,我们认为这是汶川地震芦山地震前的疑似慢地震事件。初步应用表明,本文所用的方法对于从宽频带连续波形资料中提取NVT信号是可行的。
An algorithm for detection of low-frequency seismic event is developed and applied to detect low-frequency event before the 2008 Wenchuan and the 2013 Lushan earthquakes.Continuous vertical-component waveforms of some broad band stations in a few months surrounding the Wenchuan earthquake and Lushan earthquake have been processed by applying a bandpass filter in 2—8Hz,converted to envelopes with a smoothing time of10 swindow and a median filter with a 20 min window.As a result,teleseismic,long-period noise and local small earthquakes are removed,the filtered amplitude is obviously larger than that of noise and last for a dozen of minutes to several hours during a few days for a small number of stations before the Wenchuan earthquake and Lushan earthquake,respectively.The waveform and envelope are similar to that of non-volcanic tremor(NVT),we think they are suspected NVT before the two earthquakes.Preliminary application demonstrates that this algorithm is potentially useful for extracting NVT signal from continuous seismic waveforms.
引文
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