Probabilities of exceedance for prescribed peak ground accelerations (PGA) at selected southern African locations

Abstract

The direct approach of Shapira a a (1981, 1983). for estimating the probability of a defined horizontal peak ground acceleration (PGA) being exceeded at a specified location has been applied to fourteen cities in southern Africa. The analysis is based on the known seismic history of the region (south of 22° S) since the beginning of the 19th century, and assumed that the apparent seismic hazard of the past T years will continue for T years to come. The major uncertainty involved in the locations of epicentres of relatively high magnitude seismic events and the questionable validity of the attenuation equation used limits the use of the results as obtained (as well as those obtained by other methods) for high safety requirement structures, yet they may be used for the assessment of relative seismic hazard in southern Africa. The results obtained are in agreement with reported seismic intensities as well as with different evaluations of the probabilities of high seismic intensities in southern Africa.