用中国钻孔应变台网资料检验大震“前驱波”

Testing Precursory Wave before Strong Earthquakes Using Borehole Strain Data

利用中国钻孔应变台网的13个台站观测精度达10^-10-10^-8量级TJ式钻孔体应变仪观测资料,深入分析2004年12月23日澳大利亚麦阔里岛MS8.0和2004年12月26日印尼苏门答腊MS8.9大震前应变变化,对这两次地震＂前驱波＂进行了客观地检验。用高通滤波消除了周期大于128 min的固体潮汐影响,用回归分析方法消除了气压干扰。用小波变换方法将2-128 min信号分解到6个不同频段进行分析。结果显示,该方法能提取出信号中微弱变化信息。根据小波变换提取的类似＂前驱波＂基本特征,提出＂超限率＂分析方法检验小波分解的细节部分。对所有细节部分的超限率时间序列的回归直线斜率进行统计,得出了平均值和标准差,分析了正负比。这3项统计数据显示,大震前15 d之内不能普遍检测到＂前驱波＂。

We apply changes before the and to quantitativel at 13 stations. Firs borehole strainmeter data with 10^-10-10^-8 resolution to analyse strain 2004 Macquarie Island Ms8.0 and 2004 Sumatra Ms8. 9 earthquakes, y and objectively test precursory waves using high-quality observations t, to remove solid tide with period longer than 128 minutes, we filtered data with high-pass filter. Secondly, we remove air-pressure influence by linear regression method. Finally, we apply wavelet transform to analyze the high-pass filtered data, decomposing the signal within the period of 2-128 minutes into 6 different frequency bands. The result indicates that wavelet transform can be used to identify small changes existed in the deformation signal. To quantitatively analyze the characteristic precursory waves, we proposed an overrunning points ratio method to calculate overrun points in certain times. We analysed all the 6 ferequency bands and calculated the slopes of regression line, the averages, the standard deviation and the ratios of the slope that are greater than 0 and less than 0. These three kinds of data show that precursory waves can not be generally detected in the period of 15 days before the two strong earthquakes.