Near-Surface Site Characterization Using Active and Passive Surface Wave Analysis in Addis Ababa, Ethiopia

Abstract

Summary The subsurface condition of Addis Ababa city is heterogeneous and distinctly varies from place to place, ranging from soft soil formations to competent rock mass units. The aim of this study was to estimate site-specific average shear wave velocity changes within the topmost 30m (Vs30) geological medium at nine representative sites. The shear wave velocity profile in the upper 30 m of the selected sites was attained by joint dispersion inversion analysis of active-source MASW and passive-source MAM surface wave measurements. They are effective methods to estimate the shear wave velocity of shallow and deep subsurface materials. The result shows that the Vs30 calculated at the selected sites in the city varies from 256 to 1787 m/s. The study results were used for site classification of near-surface geological materials according to the Vs30 classification guideline proposed by the National Earthquake Hazards Reduction Program (NERHP) and Eurocode 8 (EC8) classification. Based on Vs30 results, the subsurface materials for the city’s selected sites are classified as site classes C and D as per NEHRP and as site classes B and C as per EC8. The findings of this study will be used for preliminary local site classification and site-specific ground response analysis.