جستجوی مقالات مرتبط با کلیدواژه « microtremors » در نشریات گروه « زمین شناسی »

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.

In this study، the local site amplification characteristics are investigated at 10 accelerometer stations organized by Tehran Disaster Mitigation and Management Organization (TDMMO) in Tehran city. The microtremor data were selected from 40 days contious recording at each station. The site amplification functions are calculated using horizontal to vertial spectral ratio (H/V) in the frequecny domain. The results revealed large sensitivy to the microteremor sources. When compared the results with previous studies using earthquake data، the computed amplification functions showed the peaks not related to the site or different amplification values at predominant peak frequencies at the sites. To find the reasons، the amplification function at the sites was calculated using microteremor data recorded at weekdays and holidays. we calculated Meanwhile، the results of calculated amplification functions for holidays showed a good agreement with those of previous studies that meansthe industrial noise largly affect the results، especially in the south of Tehran. Furthermore، It was found that the industrial noise mostly affected the frequency range of 1 to 1. 5 Hz. This also led to increase the amplification coefficient in an order of 1. 5 to 2. 2. This emphesized on the fact that the microtremor data recorded in the mega-cities like Tehran should be carefully analyzed to prevent misleading results. Furthermore، it is suggested to use microtremor data recored in the holidays to avoid such heavy industrial noise contamination.