Secrecy over SA earthquake swarm
25 February 2011 12 Comments
Augrabies region has experienced a year-long earthquake swarm which may signal a major seismic event in SA
The Hermanus Magnetic Observatory has been monitoring the earthquake swarm recorded in Augrabies region this past year. The facility forms part of the worldwide magnetic observatories network Intermagnet which monitor the Earth’s magnetic field. HMO is the regional warning centre for Africa.
Seismologists have been monitoring the Augrabies anomalies over concerns that these might be advance-warning signals for a major seismic event in SA. Top earthquake expert Dr Chris Hartnady has been issuing public warnings since February last year that a major earthquake could be hitting SA because of the rapid spread of the East African Rift fault lines.
He warned in a scientific paper in Science in Africa last year : ‘Major earthquakes can lead to large-scale loss of life and property due to building collapse, fires and landslides on unstable slopes and catastrophic disruption of dam walls and water mains – and roads, railways and fuel pipelines.” link
It’s still very difficult to predict the exact moments when earthquakes will hit, however scientists have been able to build up an average estimate of the areas where earthquakes may occur soon – due to science’s increased abilities to detect activities inside the earth’s constantly moving tectonic plates system. The problem for geologists in Africa is that there is no long-term recorded oral history of earthquakes and a very limited written record: Westerners only started recording these once they started moving into a very sparcely-populated region from the 15th century.
A veil of secrecy now seems to be drawn over the year-long earthquake swarm around the Augrabies region – which are reported in the SA news media but not by the US Geological Survey maps. Even bloggers from overseas are beginning to notice the secrecy, for instance blogger Selim_Karabiyik of a website which claims that the shallow earthquakes worldwide are caused by the approach of a mystery Planet X (also referred to as Nebaru) writes on January 28, 2011 at 10:54am: “It is really difficult to find about what has been happening in Southern Africa. I spent hours to get hold of earthquakes happening there last night and I’ll keep trying…”
The area of Augrabies has since February 2010 and as recently as last week been experiencing an ‘earthquake swarm”. These are sequences of many earthquakes in a relatively short period of time. A swarm may last in the order of days, weeks, or months, but rarely more than two years.
- They are differentiated from earthquakes succeeded by a series of aftershocks, by the observation that no single earthquake in the sequence is obviously the main shock.
As part of its national monitoring programme, the Council for Geoscience has been constantly monitoring the seismic activity in the Augrabies area. The first recorded earthquake of the present swarm occurred during February 2010 but it was only when the population felt an earthquake measuring 3.7 on the local magnitude scale on 26 July 2010, that people became aware of this seismic activity. Since then, at least five earthquakes exceeding magnitude 4 have occurred near Augrabies, the largest to date being magnitudes 4.2 and 4.9, events that occurred on 12 and 25 January, respectively.
The Augrabies area is situated on the boundary of the Kaapvaal Craton (Archean), the Kheis orogenic belt (1 800 Ma) and the Namaqua-Natal orogenic belt (1000 Ma). This area is highly deformed and there are numerous faults, shear zones, folds and other lineaments, which could provide weak areas in the crust. It also lies on strike of the Hebron fault in Namibia, which is known to have been active during recent times. Earthquake epicentres tend to lie parallel to the Orange river in that area, on both sides of the river, and the structural maps indicate a number of faults striking parallel to this trend all along the river. A possible explanation therefore is that the Orange River follows a weak zone in that area, caused by a relatively wide zone of faults, some of which are being activated by the current strain in the crust.
Rapid spread of East African Rift fault lines towards southern Africa
Dr Hartnady also warned on April 11 2010 in a report in the Daily Express that “South African is almost certain to be hit by a major earthquake. it’s not a matter of if, but when’. Hartnady of the Umvoto Africa CSIR Satellite centre said the coastal harbour cities of Durban and Cape Town are the areas most likely to be hit by an earthquake because of the rapid spread of the East African Rift fault-lines.
The UK newspaper quoted Dr Hartnady as warning that the tectonic plates of the Earth’s crust are increasingly active on the East African rift’s fault lines – and this could pose an earthquake threat to South Africa. He said: “A major earthquake disaster in the region is inevitable because wide areas of southern Africa are affected by the slow, southward spread of the East African rift system.”
Koeberg Nuclear Power Station: close to 6.2 earthquake epicentre of 200 years ago…
While precious few long-term records exist of earthquakes in this region, an 6.3 earthquake did occur in Tulbagh north of Cape Town in 1969, killing twelve people in this small rural town and leaving 60% of the working-class residents homeless;
Current Milnerton race track site hit by earthquake in 1809…
Two-hundred years earlier in 1809, the practically unpopulated Jan Biesjes Kraal farm – now the site of the Milnerton race track north of Cape Town – also was hit by an earthquake. This region also is located within a twelve-km radius of the Koeberg nuclear power station at Melkbosstrand, located at the Atlantic Ocean coast and well inside the greater Cape Town metropolitan area radius which is populated by more than 3-million people.
The UK newspaper quotes Dr Hartnady as warning that the tectonic plates of the Earth’s crust are increasingly active on the East African rift’s fault lines – and this could pose an earthquake threat to SA with increasing certainty. He was quoted as saying: “A major earthquake disaster in the region is inevitable because wide areas of southern Africa are affected by the slow, southward spread of the East African rift system. It is not a question of if, but when. The consequences would be so expensive in terms of mortality and economic cost that the risk of being ill-prepared is unacceptably high,” added Dr Hartnady, technical director of earth science consultants Umvoto Africa CSIR Satellite Applications Centre.
It’s still very difficult to predict the exact moments when earthquakes will hit, however scientists have been able to build up an average estimate of the areas where earthquakes may occur soon due to science’s increased abilities to detect activities inside the earth’s constantly moving tectonic plates system. The problem for geologists in Africa is that there is no long-term recorded oral history of earthquakes.
He warned: “Major earthquakes can lead to large-scale loss of life and property due to building collapse, fires and landslides on unstable slopes and catastrophic disruption of dam walls and water mains – and roads, railways and fuel pipelines.” The last major earthquake to hit Cape Town was in 1809, with the epicentre thought to be located at the then-Jan Biesjes Kraal farm,which later became the site of the racecourse near modern Milnerton and is located just a few kilometres away from the aging Koeberg Nuclear Power Station at Melkbosstrand – which is Africa’s only nuclear electricity-generating facility, built during the apartheid years.
- Dr Chris Hartnady is a former associate professor at the University of Cape Town and is now technical director of Umvoto Africa, an earth sciences consultancy firm (www.umvoto.com). His entire article first appeared in www.SciDev.Net at http://www.scienceinafrica.co.za/2010/february/earthquake_SA.htm