Seismic Activity in Alborz, Northern Iran,Revealed by Local Seismic Network

Historical background and instrumentally located earthquakes as well as the geological evidences all suggest that Alborz region in northern Iran is one of the seismically active regions in the Middle East. In 1996, as a part of national seismic network, the Geophysics Institute of Tehran University deployed a telemetric seismic network in Alborz region mainly to monitor local earthquakes. Relying on the records obtained during 1996-2005, several seismically active areas with the following aspects could be recognized. The epicenters of local earthquakes are in good agreement with the location of major faults as well as the regional tectonic settings. The distribution of earthquakes in eastern and western parts of the region are consistent with the related major faults. A kind of seismic quiescence exists in the central part of the Alborz around the Tehran city. A similar situation could be observed along the south eastern extension of Rudbar fault system. Most of the recorded earthquakes have shallow depths indicating that the seismic activity is mainly taking place in upper crust and the seismogenic layer has a thickness of about 20 km. Taking into account the historical background and the present situation, the occurrence of a major earthquake in Alborz in the vicinity of Tehran is not far from expectation.