Site Response Study in the Eastern Part of Guwahati City (Assam) Using Ambient Seismic Noise Analysis

摘要

North-east region of India is notoriously seismic prone and Guwahati in the state of Assam is arguably the largest city in that region. The results of site response study in the eastern part of Guwahati using ambient seismic noise carried out from Geological Survey of India as a part of a multi-institutional project are analysed and presented here.The average relative spectral ratio of horizontal to vertical component (H/V) was calculated using the Nakamura technique. The maximum site amplification factor and corresponding peak frequency maps are prepared. In this study, we compared the noise observations with spectral-ratio site response estimates using microearthquakes recorded at some sites to test the validity of the noise survey method. Our analysis shows that the site amplification factor varies from 1 to 10, while the peak frequency varies from 1 to 16 Hz. The highest amplification factor that range from 7 tolO is observed in the southeastern part of the study area (eastern part of Guwahati). The highest peak frequency has values that vary from 8 to 16 Hz, in central part of the survey area with amplification factor of 2-3. These findings may be useful for designing the building code as well as for evolving earthquake hazard mitigation model for the city.Our study concludes that the Nakamura's method may be a reliable procedure for determining the fundamental resonant frequency of sedimentary deposits from ambient noise of the site.