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.
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