Seismic Hazard Assessment of Gilan Province Including Manjil in Iran

Abstract eng:
Manjil is an important city in Gilan province in Iran. It has experienced one of the largest earthquakes in Iran on 21 June 1990 with magnitude of Ms = 7.7 Richter that caused many destructions and human casualties. With respect to historical earthquakes in the region of Gilan province and existing active faults like Manjil-Rudbar and also according to the distribution of earthquakes, this region has high seismic potential. With respect to the mentioned reasons, current study has been performed as seismic hazard analysis of Gilan province with different risk levels. It is needed to provide horizontal Peak Ground Acceleration (PGA) maps with different risk levels for different parts of the region. A category of historical and instrumental seismic data since the 4th century BC up to 2005 has been used and seismic sources in the radius of 200 km of the region have been modeled. In order to assess the seismicity parameters, with respect to the lack of proper seismic data and uncertainty of magnitudes in different times, the Kijko [2000] method has been used. In order to determine the PGA over bedrock three different attenuation relationships of Ramazi [1999], Ambaseys et al. [1996] and also Sarma and Srbulov [1996] relationships have been used. These three relationships have been mixed by using logic tree method with weighted coefficients of 0.4, 0.35 and 0.25 respectively and final results have been produced. The probabilistic hazard analysis of earthquakes has been performed for a 50*50 mesh which covers the region, by SEISRISK III [1987] for occurrence probability of 2% and 10% in 50 years.

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