SEISMIC ACTIVITY OF CENTRAL ALBORZ IN IRAN (DURING 1925-2002)

The destructive earthquake of 1990 indicated the need to install a permanent seismological network in the region. In 1995 the Institute of Geophysics of Tehran University deployed a telemetric seismic network in Alborz to monitor local earthquakes. The epicenters of local earthquakes are in agreement with the NW-SE trending major faults. The distributions of earthquakes in east and west parts are consistent with the related major faults. The majority of events are shallow indicating that the seismic activity is mainly taking place in upper crust and the seismogenic layer has a thickness of about 20 km. heterogeneous.and Structural analyses carried out in central Iran have shown that the evolution of this belt has been strongly conditioned by the inversion of pre-existent extensional faults. Inversion tectonics is related to the reactivation of grabens formed in the foreland of the Late Triassic Eo-Cimmerian orogen, resulting from the accretion of the Iranian block to Eurasia.