THE STUDY OF CRUSTAL STRUCTURE IN THE IRANIAN PLATEAU BY GRAVIMETRIC DATA BASED on GEOPOTENTIAL MODEL EIGEN-5S

Geopotential models provide reliable low frequency gravimetric data. Based on a recent study, one of the best satellite-based geopotential models of gravity field for Iranian region is EIGEN-5S. This model provides the coefficients of gravity potential function of the earth up to degree and order 150 in spherical harmonic development, which correspond to a spatial resolution of 130 km (half-wavelength).

This resolution seems to be enough for determining the large-scale crustal structures in Iran. We computed the complete Bouguer anomalies over the Iranian plateau and the seas adjacent to it using SRTM (the global digital terrain model) and the sea depth maps provided by the National Cartographic Center (NCC). The Caspian is 25.83 m below the geoid. To account for this difference in height, we first added this value to the depth of the Caspian, and then, we treated the 25.83-meter layer as a layer of rock. The Bouguer anomalies show a minimum of –268 mgal over the Zagros Mountains, which have the thickest crust in Iran. A maximum Bouguer value of 70 mgal is observed along the southern shore of the Caspian Sea. This is the region where the thicker continental crust of Iran moves towards the thinner oceanic crust of the Caspian basin.

Next, we attempt to invert the Buoguer anomalies to a moho depth model for the Iranian plateau. We do the inversion in the frequency domain using an iterative scheme to calculate the shape of moho undulations beneath the crust.