Seismic Gravity Signal Detection Based On Superconducting Gravity Data

Earthquakes cause mass redistribution in the Earth's interior,resulting in observable changes in the Earth's gravitational field.With its high sensitivity,high stability and wide dynamic frequency range,the superconducting gravimeter can detect subtle changes in gravity inside the earth,which plays an important role in recording global seismic events.It is of great scientific significance to take the observation of gravity field as an important way of seismic exploration and to analyze seismic signals by means of gravity measurement.This paper tested the superconducting gravimeter sensitivity for detection of seismic signal,and combined with effective time-frequency analysis method to analyze superconducting gravimeter records of earthquake events,to extract the seismic signal of the changes of time and the frequency component of information,such as frequency,advantage spectrum can provide earthquake cases the reference for the research on the mechanism of the earthquake.Based on the traditional time-frequency analysis method,different time-frequency analysis methods are introduced in this paper.Aiming at the defect of mode aliasing phenomenon in EMD decomposition,the improved EMD methods,EEMD and CEEMDAN,are introduced.By comparing the time-frequency analysis methods,the advantages and disadvantages of these methods are preliminarily analyzed.The results show that the timefrequency analysis method based on CEEMDAN can obtain accurate time-frequency spectrum and is a powerful tool for interpreting superconducting data.The gravity signal caused by the 2011 Tohoku earthquake M?W9.0 was studied by using the continuous second sampling records of superconducting gravimeter at Lhasa station and Apache-Point station in China.Tsoft software was used to preprocess the data,remove the tidal effect and atmospheric gravity effect,and HHT analysis method was applied to the corrected superconducting gravity data.Time spectrum and marginal spectrum of large earthquakes are established.It is found that the dominant frequency of Japan major earthquake signals is0?0.13 Hz.From the marginal spectrum,it can be seen that Lhasa station and AP station have similar energy accumulation.In addition,in order to eliminate the influence of the instrument itself,the AP station was used to study three earthquakes of different magnitude,including the Tohoku earthquake in Japan,and analyze the time-frequency characteristics of the SG records.The results show that the three seismic signals are concentrated in the frequency of 0.06 Hz,and the energy accumulation corresponding to the dominant frequency is proportional to the magnitude.The above analysis also proves that SG data is an important information source for detecting excitation signals of large earthquakes and provides reference value for studying the response of relevant strong earthquakes.