A Seismic investigation of the upper crustal structure of the Iranian plateau

We obtained a three-dimensional (3D) shear wave velocity model of the upper crust of the Iranian Plateau, based on the inversion of fundamental mode Rayleigh wave group velocity. The surface wave group velocity measurements for the period range 5-25 s were extracted from two seismic data sets: ambient noise cross-correlations and regional earthquakes. The low shear wave velocity (Vs) anomalies of the upper crust correspond to regions of thick sediments. The surrounding basins of the Plateau, the South Caspian Basin (SCB) in the north and the Zagros Fold-Thrust Belt (ZFTB) and the Makran accretionary wedge in the south form the thickest sedimentary covers of the region exceeding 20 km. The thickest parts of inland basins such as the Jazmurian depression and the Dasht-e Kavir are ~10 km. The Vs structure of southern Zagros is almost homogeneous at all levels of the crust, but the low velocity anomaly beneath the southern Lorestan Arc separates the central Zagros from the northernmost Zagros. The volcanic belt of the Makran Subduction Zone forms another large/deep low velocity zone, where the observed low Vs possibly results from magma migration and heat transfer from the mantle wedge of the subduction zone. High velocity regions in the upper crust are observed in the Sanandaj-Sirjan Zone (SSZ), the Urmia-Dokhtar Magmatic Assemblage (UDMA), and in the south of the Lut Block.