Abdolhossein Fallahi; Meghdad Samaei; Jafar Karashi
Abstract
In the current study, using microtremor measurements at 15 stations of strong ground motion network in North-western Iran, dominant frequency is determined and sites are categorized. After correction of raw data, horizontal to vertical spectral ratio is calculated and the frequency corresponding to the ...
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In the current study, using microtremor measurements at 15 stations of strong ground motion network in North-western Iran, dominant frequency is determined and sites are categorized. After correction of raw data, horizontal to vertical spectral ratio is calculated and the frequency corresponding to the greatest amplitude is acknowledged as the dominant frequency. Also at 11 stations with good quality of recorded microtremors, horizontal to vertical ratio of earthquake motion is calculated. Agreement between these two spectral ratios is quite satisfactory. Maximum and minimum observed dominant frequencies are 1.72 and 7.34 respectively. Correspondingly, using past studies, shear wave at the top 30 m ( ) is estimated and based on different seismic codes, sites are categorized. If the categorization based on predominant frequency is compared with categorization based on reported by building and housing research center, dramatic differences will be observed. These differences could be attributed to uncertainties in reported Vs30 as well as estimated dominant frequencies.
M. Samaei; A. Barzegari; M .R. Ghavimipanah; F. Ja’afari; A. Shami
Abstract
Tehran metropolitan with a high population, existence of active faults, evidence of historical earthquakes and vulnerability of its infrastructures is exposed to a high seismic risk. In the present study, considering geological reports and papers published in the past decade, three scenario earthquakes ...
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Tehran metropolitan with a high population, existence of active faults, evidence of historical earthquakes and vulnerability of its infrastructures is exposed to a high seismic risk. In the present study, considering geological reports and papers published in the past decade, three scenario earthquakes for rupture of Mosha, Niavaran and Parchin faults are presented, and synthetic accelerograms were simulated in the Tehran metropolitan. Stochastic point source method with modification of distance parameter for considering finite fault effects is adopted; and results of studies carried out by International Institute of Earthquake Engineering and Seismology (IIEES) in the recent years have been considered to account for site effects. Simulation results show considerable PGA values for Niavaran fault rupture in northern Tehran and for Parchin fault rupture in southern Tehran; also average Modified Mercali Intensity (MMI) for these scenarios are equal to IX for districts 3 and 1 in Tehran, which indicates high damage potential in those areas. Using the simulation results, we have also carried out a preliminary estimation of casualty based on the assumed scenario earthquakes. Casualty (death toll) for rupture scenarios of Mosha, Niavaran and Parchin faults are estimated to be about 5000, 117000 and 85000, respectively.
