Site effect assessment using microtremor measurement, equivalent linear method, and artificial neural network (case study: Babol, Iran)

Abstract

Site effect assessment is an important procedure for a reliable site-specific hazard assessment. Fundamental frequency is a very important factor that must be considered in a construction site for examining the potential damage resulting from earthquake. In the two last decades, the microtremor H/V spectral ratio method has been widely used for site effect studies. Microtremor measurement is fast, applicable, and cost-effective. Microtremor measurement was undertaken at 60 stations in the Babol, north of Iran, during 2011 and 2012. Regarding Nakamura’s method, H/V spectral ratios, fundamental frequency, and amplification factor were calculated for all microtremor stations. The obtained results were controlled with SESAME guidelines. In order to assess the accuracy of the microtremor measurements and its application in site effect evaluation, a preliminary site response modeling was carried out using the equivalent linear methods at some stations. More than 18 boreholes in the study area were modeled as multilayer column, overlaid on bedrock. Also, the artificial neural networks (ANN) with different inputs including thickness, type of soil, unit weight, shear wave velocity, and max shear modulus of soil layer were trained. Then, the trained ANN predicts the fundamental frequency, and the output results were compared with microtremor measurement. The results showed that microtremor measurement approach provides an acceptable means of site effect evaluation in the study area.