Detecting geophysical signals in gravity satellite missions

SUMMARY Geophysical events implying a large mass displacement especially in the vertical direction can produce a localized change of the Earth gravity field. The Sumatra earthquake of 2004 December is an example of this kind of geophysical phenomena. The aim of this work is to investigate the possibility of detecting such gravimetric changes by exploiting the information coming from gravity space missions. Proper testing procedures to be directly applied into the observation space have been set up. They require to propagate the effect of the geophysical event to the satellite observables and then to compare their track-wise spectra with the instrument noise level. These testing procedures have been applied to a realistic simulation of the gravimetric signal generated by the Sumatra earthquake, considering three different geodetic missions: the forthcoming GOCE mission, recovering a full gravity-gradient tensor, the presently flying GRACE mission, collecting low-low satellite-to-satellite tracking (SST) observations and a possible future gravimetric mission based on the same principle of GRACE, but with an improved accuracy thanks to the use of laser doppler interferometry. The results of the simulations confirm the higher capability of the SST missions of detecting gravity variations due to geophysical phenomena like the Sumatra earthquake. However, this signal could be seen also by a gradiometric mission like GOCE on condition that a considerable amount of observations is collected over the study area after the event.