Twentieth century seismicity of the Koffiefontein region (Free State, South Africa): consistent determination of earthquake catalogue parameters from mixed data types

Abstract

The preparation of earthquake catalogues for seismic hazard analysis requires the use of uniform parameters, in particular for magnitudes, although the original data include a variety of formats, such as macroseismic intensities and various instrumental mag- nitude scales. In regions of low seismicity, such as South Africa, data are generally sparse and not always suffi- cient to develop locally calibrated conversion relations. They can nevertheless be used to test the applicability of imported conversion relations, as well as their consis- tency. The Koffiefontein region of South Africa pro- vides a good test case in view of its somewhat higher level of seismicity, and central geographic location with- in the country. This paper reviews determinations of location and magnitude parameters for a suite of moderate-to-large earthquakes that have occurred in this region between 1903 and 1985.