Abstract:
We analyzed the changes/improvements of seismic event detection and location accuracy of the South African
National Seismograph Network over the last four decades. The effect of three regional velocity models on
epicentral solutions was tested during the initial study. It is shown that the hypocentral depth considered during
this study, viz. at 2 km for mining related events, and 5 km to 10 km for tectonic earthquakes, have a negligible
effect on the error in epicentre location. Further, three detection distances were evaluated during this study, viz.
300, 500 and 1000 km. The location errors decreased significantly by increasing the detecting distance. This study
highlights the importance of including 5-phase arrival times to better constrain seismic event locations.
This observation is of particular value for the 1970 to 1997 period, when only P-phases were considered during
the location procedure. Lastly, it is shown how the errors in epicentre location decrease with an increase in the
number and geographical distribution of seismic stations.
