The Sunday Mail
Kwangwari Jera Marimira —
The main causes of earthquakes in Zimbabwe are largely plate tectonics closely related to the East African Rift System. This major geological structure accounts for 90 percent moderate to large earthquakes in Africa.
Its branches run along the eastern highlands of Zimbabwe, and its western extension covers areas around the western region of Zimbabwe, Kariba, mid-Zambezi basin; going as far as Zambia.
Mining-related seismicity has been recorded in Matabeleland South and the Midlands thus most of the earthquakes in these regions are linked to mining.
The Kariba dam has been observed to generate small to moderate size-induced earthquakes since its impoundment thus reservoir-induced seismicity is still being recorded in the region of Kariba dam.
Zimbabwe is prone to earthquakes and, therefore, can experience earthquakes of bigger magnitudes at any given time.
Although Zimbabwe is considered a low seismic zone, earthquakes of magnitudes more than 4,0 have been recorded.
In 2016 alone, Zimbabwe recorded over 50 earthquakes ranging from magnitude 1,5 to 4,6, and some were felt in Kariba, Karoi, Bulawayo and Chipinge.
The filling of the world’s largest artificial lake at Kariba has been accompanied and followed by considerable earthquake activity.
Although most of the earthquakes in our database are not recorded as felt earthquakes, they are detected by our seismic stations.
The February 22, 2006 Mozambique earthquake Mw = 7.2A, which killed four people near the Zimbabwe-Mozambique border and caused a lot of destruction, especially in Chipinge and surrounding areas, is a cause for concern.
Zimbabwe has experienced moderate earthquakes, especially in the eastern parts, Kariba and, of late, the Nyamandhlovu area near Bulawayo.
The largest earthquake to be recorded in Zimbabwe occurred at Kariba dam in 1963, and had a magnitude of 6,3.
It occurred after the impoundment of the dam, and most earthquakes that occur in this area are attributed to the dam (reservoir).
Some of the latest events which were felt in Zimbabwe include the July 10, 2013 earthquake, which occurred near our border with Botswana and the magnitude was 4,2.
The event was felt by people in the Siganacha area under Chief Malaba.
On May 6, 2014, an earthquake of magnitude 4 was felt and recorded in Kariba.
No damage was reported.
On Saturday, January 9, 2016, a 4,6 magnitude earthquake hit the Kariba area and some parts of Zambia. On August 23, 2016, an earthquake of magnitude 4,1 was experienced north of Karoi.
And on September 22, 2016, an earthquake was felt in Chipinge and the surrounding areas. This was a 5,6 earthquake, which occurred in Mozambique.
Predicting earthquakes
The number of earthquakes per year has seen significant variation, but the overall trend shows an increasing frequency.
One likely explanation for this is that earthquake detection centres have become more advanced and span the globe, and so are more likely to pick up seismic activity.
As a result of the improvements in communications and the increased interest in natural disasters, the public now learns about earthquakes more quickly than ever before.
Although we cannot predict earthquakes (globally), we can learn from the past earthquakes to map earthquake prone regions.
We have been recording earthquakes in Zimbabwe and surrounding areas so we think earthquake occurrence would continue although it should be noted that these are natural occurrences.
Detecting earthquakes/tremors
Zimbabwe has been monitoring earthquakes since 1959 when the first seismic station was installed in Bulawayo through the Meteorological Services Department.
Since then, continuous earthquake monitoring has been done by the department’s seismology section located in Bulawayo at Goetz Observatory.
There is a network comprising four broadband stations in Chipinge, Karoi, Bulawayo and Matopos, and these stations send data to Goetz Observatory, the National Data Centre, where data analysis is carried out.
Seismic monitoring equipment (seismometers) records the earthquakes to determine the epicentre for local, regional and global earthquakes depending on their magnitudes.
Earthquakes do not respect boundaries thus if a big earthquake occurs in the region, the seismic energy that radiates from the hypo-centre (focus or heart of the earthquake) in the form of seismic waves can travel and affect places in different parts of the region.
This can be seen by the Mozambique 2006 earthquake and the recent Botswana 2017 earthquake.
The shaking from these earthquakes was felt in most parts of the country, but the epicentre(s) were in Mozambique and Botswana, respectively.
The Goetz Observatory is affiliated to regional and international institutions where data-sharing is promoted; thus Zimbabwe also has access to stations from the region; for example, stations in South Africa, Botswana, Zambia, Mozambique, Namibia and others.
There is no scientifically plausible way of predicting the occurrence of a particular earthquake; that is the magnitude, time of occurrence and location of the future earthquake.
The Meteorological Services Department, through the Seismology Section, has been educating people on earthquake risk and earthquake-related disaster preparedness.
The department has participated in the design of disaster risk management plans for different districts and provinces, thereby contributing to people understanding how prone their region is to earthquakes.
The coordination of activities like the preparation of national, provincial and district disaster risk management plans is done by the Department of Civil Protection with the participation of different departments like MSD.
The MSD is always open for people to visit and learn more about earthquakes. In fact, a number of school children have been educated on earthquakes and related hazards.
The department is also participating in national and provincial agricultural shows where people can get more information and material on earthquakes and related disasters.
Before an earthquake:
◆ Support the adoption and enforcement of building codes that have suitable requirements for earthquake-resistant design.
◆ Check your home for earthquake hazards. Bolt down or provide other strong support for items that can easily fall.
◆ Teach responsible members of your family how to turn off electricity, gas or water at the main switches, valves and taps.
◆ Have your family receive instruction in basic first aid because medical facilities may be overloaded immediately after a severe earthquake.
◆ Know emergency telephone numbers (doctor, hospital, police, etc).
During an earthquake:
◆ Drop, cover and hold on!
◆ Move as little as possible — most injuries during earthquakes occur because of people moving around, falling and suffering sprains, fractures and head injuries.
◆ If indoors, watch for falling plaster, bricks, light fixtures, high bookcases, and other furniture which might slide or topple.
◆ Stay away from windows, mirrors, and chimneys. If in danger, get under a table, desk, or bed; in a corner away from windows; or in a strong doorway.
◆ If in a high-rise office building, get under a desk. Do not dash for exits, since stairways may be broken and jammed with people. Power for elevators may fail.
◆ If outside, avoid high buildings, walls, and power poles. Move to an open area away from all hazards.
◆ Most of all, remain calm!
After an earthquake:
◆ Apply first aid or seek medical help for injured people.
◆ Avoid fallen power lines or objects touched by the fallen wires.
◆ Check to see that sewage lines are intact before permitting continued flushing of toilets.
◆ Do not use your telephone except for genuine emergency calls.
◆ Do not go site-seeing. Keep the streets clear for passage of emergency vehicles.
◆ Be prepared for additional earthquake shocks called “after-shocks”.
◆ Wear shoes.
◆ Clean up dangerous spills.
Mr Kwangwari Jera Marimira is the National Data Centre Manager of the Meteorological Services Department’s Seismology Section (Zimbabwe National Data Centre) based in Bulawayo. He wrote this article for The Sunday Mail.
