SITE EFFECTS IN PROVIDING EARTHQUAKE SCENARIO OF GORGAN CITY OF IRAN

The most important factors in an earthquake event are the amount of losses and financial damages, therefore a good simulation of what can happen in an event and recognizing vulnerable regions in a city and consequently estimation of amount of casualties and damages can help city managers to be ready before the events. Accordingly, one of the most important steps in developing Gorgan's earthquake scenario was estimation theamount of destruction after the earthquake. Site effects study performs an important role in determining the amount of destruction after earthquakes, beside the structural study. Our data for site study condition in Gorgan were: log data available in the offices, field study and geological reports, and soil mechanics tests from some special projects of housing and urban development organization, which we used as an important layer ofinformation in the Gorgan's earthquake scenario process. Fortunately, bores that we used have an appropriate distribution in the city, in a manner that we could study site conditions in Gorgan by relying on their information. After that we modeled the bore loges information in ProShake, and then we selected and applied an accelogram reference which used to calculate the speed, displacement and acceleration on Earth's surface for output. In comparison of input accelogram (in the bedrock) and output accelogram (calculated for the ground's surface with incorporate site effect) we can find site amplification factor in a given point. By calculation this ratio in the center of squares with 250 * 250 meters dimensions that comprise all city's area, site amplificationzoning map in the Gorgan region was provided, which was one of the information layers in developing of Gorgan earthquake scenario.