Site Response Analysis of Selected Sites of Adama City
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Date
2021-09
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Addis Ababa University
Abstract
The local soil deposits found in Adama area have the potential of seismic site amplification. Site response analysis of the study area is mainly motivated by the presence of thick local soil deposits in a seismic prone area. Compressional (P-wave), horizontally polarized shear (SH-wave) and surface waves was acquired at four sites in the study area. Multichannel Analysis of Surface Wave (MASW) and Micrometer Analysis Measurements (MAM) were used to evaluate the shear waves from the surface waves and refraction time term inversion, to evaluate shear waves from body waves. The Poisson's ratio and anisotropy of the site have been calculated using the P-wave, SV-wave and SH-wave results.
Using the results of the average shear wave velocity for a depth of 30 m (VS30), the sites were characterized as site class C according to EN 1998:2015 and site class D according to National Earthquake Hazards Reduction Program (NEHRP). The geotechnical data collected from different private and government organizations have also been used to characterize additional five sites and to generate dynamic properties such as the modulus reduction and material damping curves. The input ground motions from the Pacific Earthquake Engineering Research Center (PEER) database were selected using several criteria such as magnitude, site conditions, and target spectrum. These are then scaled to the site PGA value of 0.15g as established based on Global Seismic Hazard Assessment Program (GSHAP).
One-dimensional site response analyses have been conducted by adapting equivalent linear analysis (EQL), nonlinear analysis with Modified Kondner-Zelasko (MKZ) and General Quadratic/Hyperbaric (GQ/H) model at nine sites in the study area. The results have been presented in terms of peak ground acceleration (PGA) profiles, displacement profiles, strain profiles, and response spectra. The area shows an amplification between 1.30 and 3.73, 1.15 and 2.00, 1.25 and 2.36 in PGA value for EQL, MKZ and GQ/H models. The results indicate that the current code design spectra (EN 1998:2015) for the site class C underestimates the shaking intensity of the sites.
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Keywords
Site Response, seismic, Surface Wave