基于重力值标准差研究长宁6.0级地震活动性

A study of seismic activity of Changning M s 6.0 earthquake based on standard deviation of gravity

通过对长宁6.0级地震前后经固体潮和零点位移改正后的重力静态观测数据、重力仪实时观测标准差(S.D.)和舍弃数量(REJ)数据的分析,认为发震时检测到的重力值变化往往是重力仪震动滤波功能失效,导致重力仪读数错误。长宁6.0级地震在地震波到达之前未能观测到有效的重力异常变化信号,这是因为当重力仪震动滤波功能开启时,大于4~6倍标准差的高频噪声将被自动拒绝,重力场的瞬时变化在重力静态观测数据中反映不出来,但是这种变化可以通过S.D.指标来反映。由于S.D.值包括了重力仪自身噪声和环境震动等重力高频干扰信号,它可以用来衡量信号噪声的大小。通过对地震发生时重力仪在不同时刻记录S.D.值与地震震级相关性分析认为,地震震级与重力仪记录S.D.值呈明显的正相关关系。在记录到的21次地震中,在发震前有2次重力仪记录S.D.值有明显突变,有1次在发震前8 min观测到REJ值的突变,因此可以根据S.D.值的突变并结合重力值和REJ值的变化来预报地震和判定单次地震活动持续时间。

Through an analysis of the static observation data of gravity,the standard deviation(S.D.)and the rejection(REJ)of real-time observation data of gravimeter before and after the Ms 6.0 earthquake in Changning,the authors hold that the change of gravity value detected during vibration is usually the mistaken reading of gravimeter caused by the failure of vibration filtering function of gravimeter.In this earthquake of Ms 6.0,no effective signal of gravity anomaly was observed before the arrival of seismic wave,and this is because high-frequency noise greater than 4 to 6 standard deviations is automatically rejected when the gravimeter vibration filtering function is turned on,transient changes in the gravitational field are not reflected in static gravity observations,but can be reflected by the S.D.indicator.Since the value of S.D.includes high frequency interference signals such as gravimeter's own noise and environment vibration,it can be used to measure the size of signal noise.By analyzing the correlation between the S.D.value recorded by gravimeter and the earthquake magnitude in different time spans when the earthquake occurs,it is concluded that the earthquake magnitude and the S.D.value recorded by gravimeter have a significant positive correlation.Among the 21 earthquakes recorded,2 had significant changes in S.D values recorded by gravimeters prior to the earthquake and a sudden change of REJ value was observed 8 minutes before the earthquake.It can therefore be held that the earthquake can be predicted in advance and the duration of single earthquake activity can be judged according to the sudden change of S.D.value,the change of gravity value and the REJ value.