عنوان مقاله [English]
Local site effects play a very important role in changing (amplification or de-amplification) the seismic haracteristics of ground motions. The objective of this paper is to investigate local ground response in an alluvium region in Mahshahr Port, in the southern part of Iran. In this regard, to perform dynamic analysis, the dynamic properties of the soil layers are determined from geotechnical tests, performed at 10 borehole stations, and, on the basis of the seismicity characteristics of the bedrock, 15 accelerograms of various earthquakes around the world are selected. Considering the local topography and soil conditions, one dimensional equivalent linear analysis is used and the results are presented in terms of microzonation maps and a site specific design spectrum. The results indicate considerable seismic amplification in the case of weak to moderate earthquakes and de-amplification of waves in strong ground motions. Because of the low stiffness of alluvium soil layers in the area, the amplified values of maximum ground velocity and acceleration are considerable during moderate earthquakes, whereas the non-linear soil behavior at higher levels of ground motion is quite evident, leading to de-amplification of the seismic waves.The specific design spectrum of the site is smaller than that recommended by the standard design spectrum of Iran (standard No. 2800), due to the non-linear soil behavior. The great deviations of the specific design spectrum of the studied site from the normal design spectrum of the 2800 Iran standard, denotes the fact that, in many areas, site specific design spectrum studies are of great importance.