Variation of Seismic b-value in Central Alborz Mountains, Iran

Abstract

The Alborz Mountains is an arc shape fold and thrust belt surrounding the south of the Caspian Sea. The geology of the Alborz Mountains is controlled largely by major thrust faults. The Mosha fault is the most prominent structure in the southern part of the Central Alborz region. It is an active, high dip angle reverse fault with an approximate length of 400 km. Damavand volcano is situated 20 km northwards from the Mosha active fault and lies unconformably upon folds and thrusts. We calculated the frequency-magnitude distribution in the Central Alborz Mountains, Iran. The earthquake catalogue used in this study consists of 895 local events recorded by the Iranian Seismic Telemetry Network from 1996 to 2006. The seismic array consists of 19 permanent stations equipped with 3-components short period (SS1) seismometers. We generated a spatial 3-D variation of b-value in the Central Alborz Mountains. A distinctive area of high b-value is found around the metropolitan Tehran. This result is well consistent with the conspicuous low velocity region derived from local earthquake tomography, coordinate of Damavand Volcano and a geothermal reservoir of 550 km2 in this region.