Reappraisal of Single-Station Locations Reported by the South African National Seismograph Network during the Period 2000-2005

Abstract

Online Material: Tables of explosions, mining‐related events, and tectonic earthquakes located during this study. During the period October 2000 to December 2005, 5806 regional earthquake epicenters were determined during routine analysis with the SEISAN software (Ottemoller et al. , 2012) as recorded by the South African National Seismograph Network (SANSN). A total of 1380 of these epicenters were determined through the three‐component single‐station location method (Roberts et al. , 1989), as implemented within the SEISAN software (Ottemoller et al. , 2012). These events, located through the single‐station location method, are included in the South African National Seismological Database (SANSD), with magnitudes ranging from M −0.9 to 4.4. The area of interest and the geographic distribution of data reported in this study are shown in Figure 1. The solid black circles denote events recorded through the iterative least‐squares method, and the gray circles denote events located with the single‐station location method. The polygons with black outlines define seismic clusters (Du Plessis, 1996) and the hatched polygon the Wits basin (Singh et al. , 2009). Figure 1. The study area (inset) and distribution of earthquake epicenters determined through the single‐station (gray circles) and multistation least‐squares (black circles) location methods during the period October 2000–December 2005. The polygons outlined with black borders demarcate seismic clusters defined by Du Plessis (1996): 1, Springbok/Kamieskroon; 2, Grootvloer; 3, Ceres; 4, Koffiefontein; 5, eastern Lesotho; 6, Matatiele; and 7, Phalaborwa. The broken lines indicated as 8 and 9 on the map show the extent of the Kango–Baviaanskloof and Worcester faults, respectively (Du Plessis, 1996). The hatched polygon (10) defines the Wits basin (Singh et al. , 2009). Clusters related to mining operations are indicated in Figure 5. The practice of evaluating earthquake epicenters at the Council for Geoscience (CGS) with the single‐station method was introduced as a result of an …