Discrepancies between free air gravity anomalies from EGM2008 and the ones from dense gravity/GPS observations at west Sichuan Basin

Recently we built a dense regional observation network,which is made up of 302stations,at the west of Sichuan Basin,and carried out a gravity/GPS hybrid observation campaign.The aim is to get the detailed features of the Free-air Gravity Anomaly(FGA)at the study area,and to evaluate the quality of the modeled results of EGM2008.As a whole the observed FGAs are negative.They change slowly from about-160×10-5 ms-2 at west to-60×10-5 ms-2 at east of the study area.The modeled FGAs from EGM2008consist well with the topography of the west of Sichuan Basin.There exist visible modeled gravity gradient belts at both Longquan Mountain and the boundary of Sichuan Basin and Tibetan Plateau.At the southeast of the study area the modeled FGAs are about-50×10-5 ms-2.However,at the Chengdu plain to the west of Longquan Mountain,the modeled FGAs become as large as-120×10-5 ms-2 or so.The discrepancies between the modeled FGAs and the observed ones change slightly round-10×10-5 ms-2 at most points of our observation network,indicating that the EGM2008can recover the total distribution shape of the earth gravitational field in the study area.If adjusted by a number of observation results in situ at the earth′s surface,the EGM2008will reflect well the real gravitational field of the earth.