SEISMICITY OF SOUTHERN AFRICA DURING 2006 WITH SPECIAL REFERENCE TO THE MW 7 MACHAZE EARTHQUAKE

Abstract

Seismic activity recorded by the South African National Seismograph Network in southern Africa during the period January to December 2006 is summarized in this article. The South African National Seismograph Network was expanded to 23 seismological stations and the data communication infrastructure updated to transmit continuous waveform data in near real-time during 2006. Earthquake data, published in the Seismological Bulletins of the Council for Geoscience for 2006, was revisited and all tectonic earthquakes relocated together with mining related earthquakes that were located outside known mine boundaries. The resulting earthquake database comprises a total of 3875 located seismic events, the majority of which (79%) is located in the gold and platinum mines of South Africa. A total of 1460 events were ascribed to chemical explosions in opencast mines and quarries and flagged accordingly in the database. The recorded seismic activity, tectonic as well as mining-related, is discussed in terms of the error in location and the observed frequency-magnitude distribution. A fault plane solution for a M L =4.0 earthquake, located in the gold mines of South Africa, is also presented. The most significant earthquake occurred on the southernmost extension of the East African Rift System in south-western Mozambique and measured 7.0 on the moment magnitude scale. The earthquake was widely felt throughout the region, causing four fatalities, 27 injuries and damage to approximately 160 buildings.