J Asadifallah; M Zare; M.R Gheytanchi
Abstract
Natural frequency of soil is an important factor in site effect studies. In order to determine this parameter, microtremor measurements were applied as a fast, simple and economic tool. For this purpose, microtremors were recorded in 74 points with time durations of 5 to 10 minutes throughout the city ...
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Natural frequency of soil is an important factor in site effect studies. In order to determine this parameter, microtremor measurements were applied as a fast, simple and economic tool. For this purpose, microtremors were recorded in 74 points with time durations of 5 to 10 minutes throughout the city of Shiraz. Natural frequency and amplification factor of soil were then estimated considering the main peak in spectral ratio between horizontal and vertical components (H/V) that is also known as Nakamura’s technique. Fourier and power spectrums were also used to determine this spectral ratio. The results demonstrate that natural frequency varies from 0.5HZ to 6HZ in different parts of the city, so that it increases in the east and north part of the city where alluvial deposits over the bedrock are thin. Also, amplification factor of the alluvial deposits obtained by this method has values between 1.3 and 5 throughout the city. In order to investigate time-dependence of the natural frequency, after 8 years of data recording new data were recorded in five stations. The results indicate acceptable correlation and consistency between old and new data results in these five stations.
Z Asadi; M Zare
Abstract
Understanding paleoseismic characteristics and seismic capability of faults is very important for evaluation of seismic risk in any area. Using geomorphic markers as indirect method in paleoseismic studies is an appropriate and practical method in understanding the tectonic activity the mountainous areas. ...
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Understanding paleoseismic characteristics and seismic capability of faults is very important for evaluation of seismic risk in any area. Using geomorphic markers as indirect method in paleoseismic studies is an appropriate and practical method in understanding the tectonic activity the mountainous areas. Gigantic landslides are among the markers for this purpose. Usually these landslides are related to tectonics and it is generally interpreted as landslides triggered by earthquakes. Major landslides in the Noor valley (Central Alborz) are used in this study as geomorphic markers for seismic capability of faults. No major historical earthquake is reported from the Noor valley arae, however gigantic landslides in the valley indicate that multiple major seismic events have occurred in earlier periods which are not recorded in historical records. According to geomorphic characteristics of these landslides, we determined 3 different age classes (Late Holocene, Early Holocene, and Late Pleistocene) for them. These ages provides possibility for identifying of multiple earthquake events in the area. According to the relationship between the earthquake magnitude and the maximal volume of the related landslides, we estimated magnitudes of the earthquakes to be 7.7±0.49 to 7.9±0.49. Based on the distribution of the landslides the eastern segment of the Baladeh fault seems to be responsible for the earthquakes.
