Statistical evaluation of seismic event location accuracy by the South African National Seismograph Network over four decades

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.