Understanding the seismicity and tectonic patterns along the east coast of South Africa using geophysical and geospatial techniques

Abstract

The seismicity and seismotectonic setting of KwaZulu-Natal were studied using macroseismic data from two recent earthquakes in the province. It was shown that seismic activity is taking place along pre-existing zones of weakness which are currently undergoing reactivation. The earthquakes studied damaged low-cost houses more than well-built houses located in affluent suburbs, implying a greater need for strict enforcement of building codes relating to seismic loading in South Africa. An intensity-based attenuation relationship was calculated. It was shown that KwaZulu-Natal is vulnerable to tsunamis. Geophysical data was used to shed light on the crustal structure of KwaZulu-Natal. This produced 2.5D models of potential field data showing that the Natal Metamorphic Belt obducted northwards onto the southern margin of the Kaapvaal Craton where tectonic activity is still taking place. The approach of using 2.5D modelling of gravity and magnetic data applied in this study may serve as a benchmark procedure of seismogenic source delineation in South Africa.