The South African National Seismograph Network

Seismic monitoring in South Africa prior to 1970 was through sporadic deployment of seismographs by various institutions. The first was a Wiechert seismograph installed at Union Observatory in Johannesburg in 1910 to monitor mining-related earthquakes (Gane 1939). Table 1, after Wright and Fernandez (2003), shows in brief the monitoring status in South Africa for the period 1910 to 1981. Following the devastating magnitude 6.3 earthquake in Western Cape Province during September 1969, the Geological Survey (now the Council for Geoscience) deployed seven seismographs in South Africa and heralded the start of organized seismic monitoring in the country and the establishment of the South African National Seismograph Network (SANSN). The network expanded during the following years to a maximum of 27 stations in 1997. The SANSN remained analog until 1991 when a number of digital seismographs were installed either in parallel with existing analog equipment or as new stations. Data communication with digital stations was facilitated through dial-up landlines (Fernandez et al. 1991). With the advent of Global System for Mobile Communications (GSM) in South Africa, a limited number of stations were equipped with dial-up cellular modems. The SANSN was modernized during 2003 through a government grant that facilitated the purchase and installation of three-component extended short-period (30 s) and broadband (100 s) sensors. This marked a turning point for the SANSN because prior to the upgrade the network largely consisted of vertical-component short-period sensors. View this table: TABLE 1 Seismic Instrumentation Deployed in South Africa During the Period 1910 to 1981 (after Wright and Fernandez 2003 ) The lessons learned from the delay in waveform data transfer after the magnitude 5.3 earthquake in Stilfontein (Klerksdorp gold mines) on 9 March 2005 (see figure 1 for damage to a building in the central business district of Stilfontein and figure 2 for a seismogram of the …