Seismic microzonation of earth's surface layers using borehole data and shear wave velocity analysis Case study; Gorgan, Iran

Abstract

The most important factors in an earthquake are the casualties and financial losses, therefore it can help city managers to be ready before the events by a good simulation of what can happen in such disaster and recognizing vulnerable regions and consequently estimation of the amount of casualties and damages. Accordingly, one of the most important steps in developing Gorgan's earthquake scenario was estimation the amount of destruction after the earthquake. Beside the site study, site effects study performs an important role in determining the amount of destruction after earthquakes. Our data for site study condition in Gorgan were: log data available in the offices, field study and geological reports, and soil geotechnical tests done by some special housing projects and urban development organization, used as important information 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 modelled the bore loges information in Pro-Shake, and then we selected and applied an referenced accelerogram which used to calculate shear wave velocity, displacement and acceleration on Earth's surface for output. In comparison of input accelerogram and output accelerogram we can find site amplification factor in a given point. By calculating this ratio in the center of squares with 250*250 meters dimensions, site amplification zoning map in the Gorgan region was provided, which was one of the information layers in developing of Gorgan earthquake scenario.