September 29, 1969 Earthquake: Cape Province, South Africa

1969 Sept 29, 20:03:30.59 UTC, 33.268 N 19.386 E, magnitude 6.3 Mw (reference #10476)

12 killed, much property damage in Tulbagh and Wolseley. (reference #45)

The Cape Province fold zone and the Karoo have been the site of recent tectonic movement and their seismicity is far from negligible [92]; however, the earthquake of 29 September is the strongest that has occurred in South Africa in historical times. Severe damage was caused to the towns of Tulbagh, Wolseley, Ceres and Prince Alfred; 9 persons were killed and several dozens injured; some forest fires started after the earthquake [4].The macroseismic area was 650,000 km", including Cape Town, Durban and Springbok. Damage to well-built houses was greatest in the Groot Winterhoek valley, along a line joining two faults running NE.-SW. (Saron fault and Groenhof fault). Damage to older buildings of poor quality was greater in valleys where there are thick alluvial deposits; the total damage was estimated at U.S.$24 million [1, report of Geological Service, Pretoria]. (reference #1039)

A damaging earthquake occurred on 29 September 1969 in the Boland region of the Western Cape. Maximum MMI values reached IX in the epicentral area. The shaking was felt throughout the country, with felt reports from as far as Durban (Fig. 15.6). The local magnitude of the event was determined to be ML6.3. This was one of the most destructive earthquakes in South Africa, resulting in the deaths of 12 people, with many more injured. Many buildings in the Ceres–Tulbagh area suffered serious damage, varying from the almost total destruction of old and poorly built buildings to large cracks appearing in those that were better constructed and in tarred roads (Keyser, 1974). The earthquake also caused numerous landslides and rock-falls in the mountains, some leading to bush fires. Damage worth about US$24 million was reported. The main earthquake was followed by a long sequence of aftershocks, the most severe of which occurred on 14 April 1970 and had a local magnitude of ML5.7. A comprehensive report on the 1969 Boland earthquake was prepared by Van Wyk and Kent (1974) covering: the geology of the Ceres–Tulbagh area; the seismic history of the southwestern Cape; macroseismic observations; hydrological phenomena associated with the earthquake; the earthquake aftershocks; focal mechanism of the earthquake; geophysical implications of the whole earthquake sequence during 1969–1971; some elements of seismic risk assessment; and earthquake resistant building recommendations. (reference #13028)