Comparison and quantitative study of vulnerability/damage curves in South Africa

Abstract

Southern Africa is considered a stable continental region in spite of several reported medium size earthquakes, some of which caused considerable damage and casualties. The 1969 Ceres 6.3 magnitude earthquake is considered the most destructive and caused serious damage estimated at US$24 million, with 12 mortalities and many more injured. Others include six mining related tremors which caused significant damage i.e. Welkom 1976, Klerksdorp 1977, Welkom 1989 and Carletonville 1992 seismic events. Notable for their damage to infrastructure was the 9th March 2005 Stilfontein event near Klerksdorp and 5th August 2014 event near Orkney. Most buildings and structures in South Africa are not designed to resist even relatively low intensity earthquake. Most architects, engineers and builders in South Africa do not consider seismic resistance as a design requirement. In this work, potential damage caused by strong earthquake was estimated for three classes of buildings situated in Sandton, Cape Town, Durban and Port Elizabeth. The effect of earthquakes causing damage was studied by considering the “worst case-scenario”, i.e. the occurrence of an earthquake with the maximum possible magnitude for an area. In four studied urban areas, expected damage was estimated for three classes of buildings: unreinforced masonry, bearing wall, low rise, reinforced concrete shear wall, without moment resisting frame, medium rise, and reinforced concrete shear wall, without moment resisting frame, high rise. The results of the analysis showed that in case of occurrence of a strong earthquake, the most damage is expected for the building classified as ‘unreinforced masonry, bearing wall, low rise, and reinforced concrete shear wall’.