应城MS4.9地震前第二类地脉动信号异常分析

2019-12-26应城M_S4.9地震前，襄阳重力台记录到第二类(double frequency, DF)地脉动信号持续增强异常。对比全球能量辐射模型(ASSM)及西太平洋台风数据发现，震前10 h左右的DF地脉动增强及优势频率增大的异常与西太平洋Phanfone台风靠近中国大陆这一远场信号源关系较弱，与本地未知近场同源同频信号有关。结合恩施重力台观测分析认为，该异常信号不属于应城地震前的慢地震事件。此外研究发现，长江中游巴东-秭归段和襄樊-广济断裂及其邻近区域5次M_S4.0以上地震中的4次都与七曜山-金佛山断裂附近发生的M_S4.5~5.0地震呈成组活动，时间间隔为0.5~1 a，且发震时间都在DF地脉动信号的高噪声水平时段内(10月~次年3月)。当恩施-襄阳DF地脉动信号基线的月中位数和众数值的差异持续4个月增加或处于高值时，研究区发生M_S4.0以上地震的可能性增加。对震前DF地脉动信号异常特征的总结可为预测未来长江中游巴东-秭归段和襄樊-广济断裂及其邻近区域M_S4.0以上地震的发生时段提供经验指标。

Study on the Anomalies of the Double Frequency Microseisms before Yingcheng Ms4.9 Earthquake

It is found that the anomalies of the double frequency (DF) microseisms in Xiangyang gravity station (XYS) before the Yingcheng M_S4.9 earthquake on December 26, 2019 is continuously enhanced. By comparing the Ardhuin seismic spectra model(ASSM) and the western Pacific typhoon data, we find that the relationship between the enhancement anomalies of DF microseisms and the dominant frequency in the 10 hours before the earthquake and the western Pacific Phanfone are weaker than that of the local unknown near field homologous frequency signal. Combined with the observation and analysis of Enshi gravity station (ENS), we consider that the anomalies signal is not a slow earthquake event before the Yingcheng earthquake. 4 of the 5 earthquakes larger thanM_S4.0 in Badong-Zigui areas and Xiangyang-Guangji fault areas have the regularity of group activity with the earthquakes withM_S4.5-5.0 near Qiyaoshan-Jinfoshan fault areas about 0.5-1 year ago. Further, their occurrence time are in the period of high noise level of DF microseisms from October to March in the next year. If the difference between the median and majority values of ENS-XYS DF microseisms baseline increases continuesly for 4 months or at a high level, it is possible to occurM_S≥4.0 earthquake in the studied area. The conclusion of the anomalies before the earthquake can provide experience and reference for the occurrence period of earthquakes greater thanM_S4.0 near Badong-Zigui areas and Xiangfan-Guangji fault areas in the future.