Site Response Analysis of Deep Sedimentary Deposits Using Electrical Resistivity Logging; Case Study: Guilan Province, Iran

Abstract

Local geology of site and its properties can influence the input seismic wave specifications dramatically such as frequency content and duration while passing through soil stratums, making it inevitable to perform site-specific ground response analysis. For such analysis, soil’s dynamic properties including shear wave velocity (Vs) and shear modulus (G) are required, which are usually obtained using laboratory or field tests, commonly too expensive and time consuming for regions having deep sedimentary deposits. Electrical resistance of ground can be put into practice as a cost-effective alternative in assessing soils dynamic properties in order to be utilized in site response analysis, since the subsurface materials such as soil and rock have unique electrical properties. In this study, the feasibility of site response analysis using electrical logging has been evaluated using field data measurements of electrical resistivity and borehole logging through Guilan province, which is located on the southern shoreline of the Caspian Sea and in a region with high seismicity having deep sedimentary deposits. Nonlinear site response analysis as well as equivalent linear one is carried out in order to obtain the spectral response of the region, separately for the eight data points of the study. The acceleration time histories were synthesized using spectral matching technique integrating with probabilistic seismic hazard analysis. According to the results, the NL and EQL response and design spectrums, which are obtained in this study, show decent agreement with Iran’s 2800 seismic design spectrum, indicating acceptable performance of site response analysis using electrical resistivity logging.