Probabilistic seismic hazard analysis for Zimbabwe

Abstract

In this study, the seismic hazards of Zimbabwe are presented as maps showing probabilistic peak ground acceleration (PGA). Seismic hazards maps have a 10% chance of exceeding the indicated ground acceleration over a 50 year period, and are prepared using a homogenized 101 year catalogue compiled for seismic moment magnitude . Two approaches of probabilistic seismic hazard assessment were applied. The first was the widely used "deductive" approach (Cornell, 1968) which integrates geological and geophysical information together with seismic event catalogues in the assessment of seismic hazards. Application of the procedure includes several steps. As a first step, this procedure requires the delineation of potential seismic zones, which is strongly influenced by historic patterns and based on independent geologic evidence or tectonic features such as faults (Atkinson, 2004; Kijko and Graham, 1998). The second method was the "parametric-historic" approach of Kijko and Graham (1998, 1999) which has been developed for regions with incomplete catalogues and does not require the subjective delineation of active seismic zones. It combines the best features of the deductive Cornell-McGuire procedure and the historic method of Veneziano et al. (1984). Four (4) ground motion prediction equations suitable for hard rock conditions in a specified region were applied in the assessment of seismic hazards. The highest levels of hazards in Zimbabwe are in the south-eastern border of the country with Mozambique, the Lake Kariba area and the mid-Zambezi basin in the vicinity of the Save-Limpopo mobile belt. Results show that assessment of seismic hazard using parametric-historic procedure to a large extent gives a “mirror” of the seismicity pattern whereas using the classic Cornell-McGuire procedure gives results that reflect the delineated pattern of seismic zones and the two methods are best used complementary of each other depending on available input data.