Preseismic Gravity Changes before Recent Earthquakes in the GRACE Satellite Observations

We have analyzed the variations of gravity field, in order to find disturbances in the vicinity of recent great earthquakes epicenter prior the events. For this purpose, we have used 9 year long time series of gravitational gradient components obtained from weekly Gravity Recovery and Climate Experiment (GRACE) solutions. The interquartile method has been used to construct the higher and lower bounds in time series to detect outlying solution outside the bounds associated with impending earthquakes. According to obtained results gravity field anomalies occur within time interval of 2-5 weeks before earthquakes. The results in this study indicate that in each case study, the unusual variations of gravity field have had different sign but the sign of two selected components of gravitational gradient tensor for each case study is same