UNDERSTANDING EARTHQUAKES: WHAT IS HAPPENING AND ITS CAUSES? Paulina Amponsah(PhD) National Data Centre Ghana Atomic Energy Commission Email:pekua2@yahoo.com (Engineers Centre, Roman Ridge, Accra. 25-04-2019)

What causes earthquakes? How, where and when it can occur OUTLINE What is an earthquake ? What causes earthquakes? How, where and when it can occur What to do before, during and after an earthquake Conclusion

What is an earthquake? An earthquake is a natural event. It cannot be stopped from happening. It is a mighty manifestation of sudden release of strain energy accumulated over time in the earth. Whenever it occurs, many lives are lost and properties are destroyed. However, their impact on life and property can be reduced greatly if advance action is taken to mitigate the risk and minimize human vulnerability.

Seismic waves

What causes earthquakes? Elastic rebound theory Over time stress in the earth builds up. Rocks deform under stress. At some point, the stress becomes so great that a rupture occurs. Some of the stored energy is released as a result of the rupture. The earth vibrates when this happens and we say an earthquake has occurred. The rupture generally occurs along fault planes in the earth’s crust.

Plate tectonics The earth’s crust and upper part of the mantle are cracked into pieces called tectonic plates (See figure on next slide). The plates move but slowly and in the process accumulate energy. The constant movement of the plates and release of energy stored cause earthquakes. Major earthquakes occur as a result of the movement along the plates.

The tectonic plates

Within the plates we have earthquakes which are called intraplate earthquakes. The earthquakes within the plates are caused by movement along fault lines. This is what we in Ghana experience. The earth’s internal pressure makes a huge slab of rock to break along a fault line. This occurs when the elastic limit of the rock is exceeded. The rock when it cannot contain the stress exerted on it breaks and releases the stored energy. The earth vibrates as a result and when we feel it we say an earthquake has occurred.

Courtesy Prof. Uzoegbo, South Africa Earthquakes radiate seismic waves that propagate from the source. They move in all directions through the earth.

History of earthquakes in Ghana Ghana is far away from the major earthquake zones of the world(See Figure on next slide ). However, the country is seismically active and therefore prone to earthquake disaster. Historical and current recorded earthquakes in the country attest to this fact. According to Junner (1941), Ambraseys and Adams (1986), Bacon and Quaah (1981) earthquakes which caused considerable damage in Ghana occurred in 1615,1636,1862 and 1939.

Earthquake belt of the world

History of earthquakes in Ghana (cont’d) The first earthquake recorded in Ghana was in 1615. This event was located at Elmina. A fortress was destroyed. In 1636, an earthquake of magnitude 5.7 struck the country. The event was located at Axim. Some miners were buried alive. In 1862, another earthquake struck the country. It was located in Accra. Magnitude 6.5, 3 people were killed. Many structures were destroyed.

1906 : Two severe shocks struck eastern Ghana; many buildings in Accra and Ho were cracked. 1939 : Most destructive earthquake observed in Ghana. 17 people were killed and many were injured. Most buildings were also destroyed. (See Plate on next slide) 1964 and 1969: Two major earth tremors struck eastern Ghana and were felt nationwide. January, February and March, 1997:Three severe shocks were felt in almost all the regional capitals. 2003 to date

Recently recorded earth tremors in Ghana 24 March, 2018 9 December, 2018 January, 2019 February, 2019 2 March, 2019 Magnitudes, less than 4

Interaction with residents of Kasoa, Weija and McCarthy Hills by Staff of National Data Centre, NNRI-GAEC and NADMO Awutu Senya East and Weija-Gbawe Municipalities

Briefing session before fieldwork, Kasoa (04/03/19)

Briefing session before fieldwork, Weija- Gbawe (26/03/19)

Training session: Kasoa, Awutu Senya Municipality NADMO staff (27/03/19)

Attentive audience, Kasoa NADMO

Seismicity of Ghana Most of the earthquakes recorded in Ghana are located near the intersection of the two major fault zones in the country namely, the Akwapim fault zone and the Coastal boundary fault. The epicenter distribution shows that the two major faults are the possible sources of the seismic activity in the country.

Seismicity map of southern Ghana On 19th March,1935 Junner wrote: “Accra is subject to earthquakes which are probably caused by adjustment along recent faults in the vicinity of the coast line”

Earthquake prone areas West of Accra where the Akwapim Fault Zone intersects the Coastal Boundary Fault. All towns along the coast of Ghana (mainly influenced by the Coastal Boundary Fault). Towns along the Akwapim Range.

What to do Before an earthquake During an earthquake After an earthquake

Check the stability of all hanging objects. Before an earthquake Check the stability of all hanging objects. All heavy materials/objects should be kept on lower shelves. Heavy appliances should be securely fastened to the floor and all heavy furniture such as bookshelves and cupboards should be anchored to the wall. Make available battery powered radio, flashlight and first aid kits. Make sure everyone knows where they are kept and how to use them.

Everyone should know the location of the electric fuse box. Make sure you acquaint yourself with the route of exit anytime you enter a building. Have earthquake drills periodically.

During an earthquake Stay calm. Protect your body from falling objects. If indoors and you cannot quickly move out go under a sturdy desk, table, bed or stand against a support column. In a crowded place do not rush out. Do not use the elevator. If outdoors stay in the open. Stay away from anything that might fall. If driving stay away from overpasses and bridges.

After an earthquake Find out if you are injured and provide first aid. Help others who are also injured. Look out for missing people. Check for leakages on pipelines, gas cylinders etc . Turn on your radio for emergency instructions. Stay away from damaged buildings. Expect aftershocks.

A scene from an earthquake in Chile Vehicles fell off when an overpass collapsed

Courtesy Dr S. Diop,South Africa

Ruins of buildings after a Mag. 6 Ruins of buildings after a Mag. 6.3 quake hit a province in southern Iran in April,2013

Poor quality material Iran quake, Mag. 6.3, 2013

Great Hanshin-Awaji Earthquake, 1995 (Kobe)

Poor quality material Courtesy Prof Uzoegbo

Zig-zag wall construction failure Courtesy Prof Uzoegbo

Conclusion It is important to recognize that the highest concentration of strategic assets and human population is concentrated in urban areas. Therefore strategies must be devised to minimize the risks posed by natural and man-made disasters that can hamper development. For our country to be resilient to earthquake disasters, we must be proactive in our planning process at both the local and national levels.

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