Relation between sedimentary layer thickness and fundamental frequency of the H/V spectra for Bangalore city

Soil amplification and topographical effects play a major role in earthquake damage to civil structures. Study of sedimentary layer thickness and behaviour under stress cycles is crucial for earthquake hazard analysis. Borehole logs for Bangalore are used to benchmark the relation between sedimentary thickness and resonant frequency of the soil layer for this region. Microtremor measurements are carried out at the locations where borehole drilling was done and the frequencies corresponding to spectral peaks of the H/V ratio are estimated, where H and V denote the horizontal and vertical spectral component of the microtremor displacement respectively. The thicknesses of the soil layer (D), obtained from borehole logs and the soil layer resonant frequencies (f r ) determined from the H/V spectral peaks are used to obtain a regression relation between them. The regression rela tion obtained is given by D = ( 58 . 29 ± 8.8) x f r -(0.95±0.1) •, Using the data from the work of Divya et al., a similar regression relation is plotted. The results obtained are in agreement with the field data. This relation can be used for computing the depth to the bedrock for Bangalore using microtremor survey at a location where borehole data is not available.