Co-seismic And Post-seismic Gravity Changes Associated With Strong Earthquakes From GRACE Satellite Data

Compared with the traditional gravity measurement,the GRACE gravity satellite system has more advantages.The new system has wide observation range,and is neither influenced from the weather nor geographical restriction.etc.It has also been confirmed that detected several coseismic gravity changes caused by strong earthquakes.This paper extracts from the GRACE data coseismic gravity changes and those of several years after the earthquake,and then compares these gravity changes with that of the latest produced by the forward conputaion of viscoelastic spherical dislocation model and the layered viscoelastic plane model so as to analyse how strong earthquake mechanism influence coseismic gravity and earth material movement.The work done in this paper and the related results obtained are as follows:1.The GRACE data of March 2016 was processed by the P3M6 decorrelation filter and was used to calculate the global gravity change by subtraction.It was found that the error of the north-south stripe waslargely reduced in the high latitude area,while there was still a large error near the equator.By processing the decorrelation-filtered GRACE data with Gaussian smoothing of 300 km,500 km,and 800 kmrespectively,we found that the larger the smoothing radius is,the better the effect of error elimination is.Meanwhile the signals such as gravity change are also weakened,thus making the geophysics signals we want not be obvious.So we must choose the appropriate smooth radius.2.The coseismic gravity changes calculated by the viscoelastic spherical dislocation model and the layered viscoelastic plane model of the Mw8.8 Chilean earthquake are-2.7 to +2.8 ?gal and-5.6 to +1.4 ?galrespectively.The changes extracted from GRACE data are-4.7 to +1.1 ?gal.They arespatially consistent.The gravity changes in the Chilean earthquake area during the 5 years after the earthquake were extracted and demonstrated that the gravity changed increasingly significantly every year in both positive and negative gravity regions.Gravity changes of feature points of hanging wall and footwall of Chilean earthquake were studied.10 years of gravity changes were focused on,from five years before the earthquake to five years after the earthquake.It is found that the amplitudes of gravity change at A and B before the earthquake are not significant,but are slightly reduced.There are steps occurring at the time of the coseismic event,running up to 0.6 ?gal and-5.3 ?gal respectively.The gravity at the two points after the earthquake increased by 3?gal and 1.7?gal respectively.3.The coseismic gravity changes calculated by the viscoelastic spherical dislocation model and the layered viscoelastic plane model of the Mw 8.6 Sumatra earthquake are-0.9 to +0.91?gal and-2.3 to +2.1?gal respectively.The changes extracted from GRACE data are-2.8~+3?gal.The coseismic gravity change is roughly equal in the amount of positive and negative changes.The consistent distribution illustrates the reliability of the GRACE satellite data,and proves that the GRACE satellite can detect a strike-slip earthquake below Mw 9.The gravity at the A and B after the earthquake increased by 1.8?gal and 1.2?gal respectively.And the gravity at the C and D after the earthquake decreased by 0.2?gal and 0.1?gal respectively.4.The simulation results of dislocation coseismic gravity changes of Mw8.8 Chilean earthquake in 2010 and Mw8.6 Sumatra earthquake in 2012 show that the simulation results of the stratified viscoelastic plane dislocation are more reliable than the results of the viscoelastic sphere dislocation simulation,and the results are closer to the results of the GRACE observations.