- © 2009 by the Seismological Society of America
In South Africa the demand for energy resources, water, and infrastructure has grown significantly in recent years. Furthermore, many coal reserves that are currently being exploited will be depleted within the next 20 years. Consequently, plans to provide alternative sources of energy are underway. Energy providers are slowly moving away from traditional coal-fired stations to gas-powered facilities, nuclear power plants, and portable pebble bed modular reactor (PBMR) units. Several dams within the country have also been constructed to accommodate the growing demand for water. In South Africa, no regulatory guidelines for seismic design of such critical facilities exist; hence engineers make use of international guidelines such as Regulatory Guide 1.208, published by the U.S. Nuclear Regulatory Commission (U.S. Nuclear Regulatory Commission 2007). Engineers also need to assess the seismic risk to formulate emergency evacuation procedures and for insurance assessment purposes.
The first step in assessing the seismic hazard and risk for any site is to develop a seismotectonic model. The area under investigation is divided into smaller zones/regions of similar tectonic setting and similar seismic potential (Cornell 1968). These zones are then used in a seismic hazard assessment model to determine return periods of certain levels of ground motion at a given site in the area in question. For example, U.S. Nuclear Regulatory Guide 1.208 (U.S. Nuclear Regulatory Commission 2007) states that regional seismological and geological investigations should be undertaken to identify seismic sources and describe the Quaternary tectonic regime. The investigations should include a comprehensive literature review (including topographic, geologic, aeromagnetic, and gravity maps, as well as aerial photos), plus focused geological reconnaissance based on the results of the literature study. Once the regions of active faults have been identified, more detailed explorations such as geologic mapping, geophysical surveying, borings, and trenching should be undertaken. Finally, the Quaternary history …