IMPLEMENTING SEISMIC MOHO DEPTHS IN GEOID COMPUTATION

Abstract

The paper studies the effect of implementing seismically estimated Moho depths in gravimetric geoid computation, instead of assuming an isostatic hypothesis to create the compensating masses, within the well-known remove-restore technique of geoid computation. Three different techniques were applied when using the seismic Moho depths in the geoid computation. In the first technique, a constant density contrast between the lower crust and the upper mantle for all topographic elements has been assumed. In the second technique, variable density contrast computed as a function of the seismic Moho depth has been assumed. In the third technique, variable density contrast computed as a function of the topographic height has been assumed. A comparison with a geoid computed using the commonly used Airy-Heiskanen isostatic model has been made. For all cases, a gravimetric geoid has been computed for a test area by applying Stokes' integral in the frequency domain using the ID-FFT technique. All geoids are scaled (fitted) to the geoid derived from GPS and levelling. A broad comparison between all geoids is carried out. The results show that using the seismic Moho depths with variable density contrast between the lower crust and upper mantle computed as a function of the seismic Moho depth improves the accuracy of the computed geoid.