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SEASONAL VARIATIONS OF EARTH'S SURFACE DEFORMATION ESTIMATED FROM GPS AND SATELLITE GRAVIMETRY

We computed and compared the vertical loading deformation from GPS and GRACE and found that at most global sites,the root mean square(RMS)of GPS coordinate time series decreased after removing the GRACE estimates,and the annual variations of the GPS height at most sites also agree well with GRACE or geophysical model estimates in the amplitude and phase.It indicates that the nonlinear seasonal GPS vertical variation is mainly caused by the geophysical loads.However,at some sites,particularly in the Antarctica,some ocean coasts and small peninsulas,large discrepancy has been found between the estimates with the two techniques.We analyzed and discussed the error sources of the discrepancies between GPS and GRACE and their effects, which is proved by a good agreement with geophysical models,and the remaining disagreement may be due to the GPS technical errors.It needs to further investigate using longer and more GPS and GRACE measurements.