利用福州gPhone重力仪检测杜鹃台风激发的第二类脉动信号

Detecting DF microseisms by gPhone gravimeter on Fuzhou seismic station during Dujuan typhoon

蕴含大气—海洋—固体地球三个圈层能量传递和耦合信息的地震噪声(2~10 s)可用于能量辐射模型检验、海底地形探测、台风中心定位、地震预测研究等工作.近年1 Hz采样的重力仪也检测到台风激发的第二类(DF)脉动.为检验信号的有效性,提出重力观测的最佳估计策略,本研究利用2015年福州地震台gPhone重力仪1 Hz重力固体潮数据,对Peterson垂直位移功率谱密度估计策略(简称:P方法)和切比雪夫滤波估计策略(简称:F方法)进行比较.和地震时刻突变增强信号的特征不同,杜鹃台风靠近中国大陆时DF频段垂直位移呈现渐变增强特点.和同区域CMG-3 ESP地震计结果有高达0.9以上的相关性.在振幅量级的比较中,P方法对近场信号有高估现象,相对误差约为0.3.在选择截止频率为0.05 Hz,通带波纹为0.01 dB的3阶切比雪夫高通滤波处理零线误差时,重力和地震计的DF频段垂直位移相对误差不超过0.1.在进行误差因素分析时,两策略间有约±0.6×(10^-6 m)^2/Hz的能量差异.而固体潮、气压的影响小于0.0003×(10^-6 m)^2/Hz,可忽略不计.采用品质因子Q=210,地震波群速度U=1800 m/s,REF模型比率r=0.8建立的ASSM合成频谱图不仅在时域内和观测结果同步达到振幅峰值,频域内也有0.95的强相关性.福州gPhone重力仪检测到杜鹃台风激发的DF脉动信号,主频为0.1599 Hz,DF频段垂直位移最大振幅为0.9×10^-6m.在讨论两个积分策略和两型仪器频散图谱差异时发现,P方法采用1024 s窗长分段消除积分引起的零线误差方法不及滤波的.F方法对6~10 s大于3 km/s的面波波群能力是不及CMG-3的.这些都需要在数据处理和分析时需要注意.

Generated by the coupling among atmosphere, ocean waves and the solid earth, microseisms in the period of 2~10 s have provided important information on the accuracy of the numerical wave modeling for seismic noise, the effect of the ocean-continent boundary, the location of the typhoon center and the abnormal before the earthquake. To evaluate the efficiency of the signal, and the applicability of the data process method, we have provided 1 Hz datum of gPhone for the Peterson vertical displacement power spectral density estimation method(abbreviation: P method) and the Chebyshev Filter one(abbreviation: P method) to comparison on Fuzhou Seismic Station in 2015. The vertical displacement of the DF microseisms which is increased gradually during DuJuan Typhoon is markedly different from the ones excited by earthquake abruptly. However, there is more than 0.9 correlation coefficient of DF vertical displacement between the two instruments(gPhone and CMG-3 ESP) in near field. Compared with the amplitude of CMG-3, the amplitude established by P method has been overestimated by near-field signal, and the relative error is about 0.3. However, since the filter parameter in F method is that, order is 3, cutoff frequency is 0.05 Hz, Passband ripple of filter is 0.01 dB, and the relative error of DF vertical displacement in F method is less than 0.1 from those in P method. Adding for Error Analysis of two method and affection for the tide and atmosphere, it is proved that the discrepancy of the power spectral density(PSD) between the two method is about ±0.6×(10^-6 m)^2/Hz. However, influence account for the tide and atmosphere which is less than 0.0003×(10^-6 m)^2/Hz can be neglected. The DF vertical displacement in ASSM which can be calculated with quality factor Q=210, the seismic wave group velocity U=1800 m/s, and the REF model ratio r=0.8 and in experiments not only reached its peak value synchronously in time domain, but also attended to be 0.95 correlation coefficient in frequency domain. So, DF microseisms have been detected by gPhone gravimeter at Fuzhou seismic station during Dujuan Typhoon. And the main frequency of the signal is about 0.1599 Hz. The largest amplitude of the signal is about 0.9×10^-6 m.When the integration strategies in two method have been account for,it is advised that the zero-line correction with 1024 s window segment in P method is poorer than with filter in F method. And calculating the dispersion spectra of the two types of instruments,g Phone is not as good as the CMG-3 for surface wave groups in the speed of larger than 3 km/s and the period from 6 to 10 s. So those are all we needed to pay attention in data processing and analysis.