N. Alidadi; A. Mahdavian
Abstract
When seismic waves pass through alluvial layers, the seismic wave amplitude increases significantly in some periods, which is known as site amplification. In this case, it can be analyzed with an analytical model of the surface response spectrum Estimates of the input response spectrum. This behavior ...
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When seismic waves pass through alluvial layers, the seismic wave amplitude increases significantly in some periods, which is known as site amplification. In this case, it can be analyzed with an analytical model of the surface response spectrum Estimates of the input response spectrum. This behavior is essential in assessing the seismic performance of the structures and vital arteries. In this paper, we investigate this effect on different layers of sand with different thicknesses for Urmia city, a metropolitan area in the North West of Iran and an earthquake prone region. 120 geotechnical boreholes were drilled in sandy layers of different thicknesses in the central and northern parts of the city. The analysis simulated artificial acceleration based on seismic hazard analysis results. By observing the spectral accelerations for different periods at the earth’s surface the spectral acceleration magnitudes of the seams were shown for different periods. Using a neural network and genetic algorithm, these coefficients were modelled. Using the evolutionary algorithm of gene expression programming, the mathematical relation was expressed in terms of sand layer thickness and different periods. However, the results obtained from the artificial neural network using the correlation coefficient and root mean square yielded more accurate results than the gene expression programming. In conclusion, the results show that by increasing the thickness of the sand layers, the amplification ratio also increases considerably for some periods. Using the modeling results, we can estimate the amplification of the sandy soils of Urmia city with different thicknesses for variables up to 4 seconds.
A Mahdavian
Abstract
The study area includes Golestan Province and is located in the North and North-East of Iran. This area contains Gonbad, Koh-e-Kurkhod and a part of Gorgan quadrangle maps. The aims of this research are as follows: detailed seismicity and Seismotectonic studies, recognition of active faults and preparing ...
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The study area includes Golestan Province and is located in the North and North-East of Iran. This area contains Gonbad, Koh-e-Kurkhod and a part of Gorgan quadrangle maps. The aims of this research are as follows: detailed seismicity and Seismotectonic studies, recognition of active faults and preparing seismic hazard zoning map based on peak ground accelerations (PGA) for difference return periods. These studies performed in order to seismic resistance of important buildings, reducing of human and economy disaster against earthquake hazards and future planning for Golestan province. This area is located in the Central Iran and Kopeh-dagh seismotectonic provinces. There are many active faults within this area and many destructive earthquakes occurred along them. For example the Atrak-Nesa earthquake of August 943 with Ms 7.4 occurred due to activity of Ashkhaneh fault (eastern segment of Takal Kuh). Many other active faults such as Khazar, Ali-Abad, Gomishan, Maraveh-Tappeh etc distinguished in this area so that this Province can be affected of reactivation of them.
Seismic zoning maps prepared base on peak ground acceleration for return periods of 475 and 2475 years. The results show the Golestan province is divided to four seismic zones as follows:The area with PGA more than 0.35g that named Very High Seismic Zone includes parts of south of province; The area with PGA between 0.3 g to 0.35g that named High Seismic Zone includes southern, eastern and north-eastern parts of province; The area with PGA between 0.25g to 0.3g that named Moderate Seismic Zone; The area with PGA less than 0.25g that named Low Seismic Zone mainly includes western and north-western parts of province.
