Dynamic soil properties of some deep trenches in Mashhad city, NE Iran

Abstract

Microtremor survey is achieved in order to evaluate the dynamical characteristics of surface layers. For this purpose, 13 trenches were selected and microtremor measurements were performed at the top and bottom of each trench. Floor spectral ratio (FRS) analysis was accomplished to obtain frequency and amplification of the trenches. The results of microtremor were compared with 1D equivalent linear analysis. Most of the fundamental frequencies obtained by 1D analysis are in good agreement with those calculated by microtremor technique. Irregularities in surface and subsurface geomorphic conditions tend to have differences in results obtained by both mentioned methods. Damping ratios were derived from the half power bandwidth method. The damping ratio varied between 2.1 in fine grain soils and 6.6 in sand soils.