Probabilistic seismic hazard analysis at selected sites in Addis Ababa, Ethiopia

Abstract

This study presents probabilistic seismic hazard analysis at three specific sites namely: Bole area (south), Nani Building site (middle) and Gulele area (north) that represent the most often encountered subsurface profiles in Addis Ababa (AA), capital city of Ethiopia. The methodology followed couples conventional PSHA with non-linear dynamic analyses of the soil column subjected to synthetic ground motions. A fully probabilistic method was used that incorporates all major uncertainties which substantially affect the hazard levels of ground motion. Reference (stiff site) seismic hazard was determined using finite fault model in which input parameters treated randomly as discussed in our companion article. The hazard at the soil surface was computed by convolving the site-specific hazard curve at stiff site with the probability distribution of the amplification function. Within period range less than 0.50 second, a statistical treatment between surface spectral acceleration, (<i>S_a^s</i>) and that of the stiff site, ((<i>S_a^s(T)</i>) fitted to quadratic model of amplification function, <i>AF(T)</i> at the same period, <i>T</i> demonstrated a reasonable correlation. The Surface hazard was estimated using the developed relation for the specified period range. Closer to the fundamental periods of the soil columns, a strong correlation was manifested at the three selected sites.