Geotechnical Seismic Microzonation Studies of Mehdishahr City- Case Study

Document Type : Original Article


1 faculty member of bhrc

2 Building and Housing Research Center

3 Kharazmi university- Faculty member

4 Tehran university- faculty member

5 Earth science research institute- faculty member

6 Building and Housing Research Center- reserach expert

7 Expert,Geoetechnics Department, Road,Housing & Urban Development Research Center.


Seismic geotechnical microzonation studies of Mehdishahr city located in the Semnan province were conducted based on seismotectonic, geoelectric, geoseismic, geotechnical and site response analysis.  Based on the seismotectonic studies, Mehdishahr city has been located on the seismic source. The town has nearly uniform acceleration and response spectrum. Based on geoelectrical data surficial ground layers were covered with coarse grained calcareous deposits with medium electrical resistance. In order to determine the subsurface specifications, geoseismic studies were carried out using seismic refraction and down hole methods. Based on the obtained results from average shear wave velocity and depths of seismic bed rock, Mehdishahr city has been located on the soil types I and II according to the standard 2800. In order to complete the investigation and further understanding of the soil type up to the depth of seismic bed rock, geotechnical studies were carried out. Based on the laboratory results most prominent soil is SW. Using other results of subsurface investigations, numbers of 24 boreholes were simulated. Site response analysis was carried out using results from geophysical, geotechnical and probabilistic earthquake hazard analysis in Mehdishahr city. Ground motion parameters such as PGA, amplification factor, natural period and velocity response spectra were calculated at ground surface levels. Distribution of these parameters as microzonation maps, were prepared for the earthquakes with return periods of 75, 475 and 2475 years. Finally, for engineering purposes, Mehdishahr area was divided in to three seismic zones, and for each considered seismic zones, standard design spectra were introduced.


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