POPULAR EXAMPLES OF DISASTROUS EARTHQUAKES
Africa is generally free from earthquake except along the edge (Morocco, Algeria and Egypt) where some earthquake have been recorded.
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In East Africa, some major earthquakes have occurred in the rift valley zone e.g. Tanzania, near the shore of Tanganyika in the December 1910 and in Kenya in January 1928. The Accra region of Ghana is the only part of West Africa that has not experienced tremors since the second half of the 18th century.
Major tremors occurs in 1867, 1906 and 1937. In the last few years, minor earth tremors have been recorded in the basement complex areas in Nigeria particularly in Oyo and Ogun state.
In 1964, earthquake measuring 8.5am struck Alaska, capital anchored was severally damaged even though the epicentre was 120km away.
THE EARTHQUAKE PROCESS
The point in the interior of the earth from where the vibration or earthquake waves originates is called the focus of the earthquake. The waves radiate upwards incomes of waves known as underground body waves. They arrive the surface in concentric circles where they are celled the surface waves. The vertically above the focus which is the same as the centre of the earthquakes. The epicentre is the point in the point on the earth surface directly above the focus or where the shock waves first hit the surface.
The instrument used in measuring the intensity of earthquake is caked seismography. The instrument records the vibration by an earthquake.
TYPES OF SHOCK WAVES
There are two type of waves which are: (i) Body waves (ii) Surface waves
- 1. BODY WAVES: this waves travel through the crust. There are two types of body wave.
- Primary Waves: this causes the coastal rocks to move backwards and forward in the direction of the wave movement.
- b. Secondary waves: this cause the coastal make to move from side to side i.e. at right angles to the direction of the wave movement.
- 2. SURFACE WAVES: this travel through the surface rocks. They are of two types
- Love waves: this causes the surface to move from side to side at right angel to the direction of the wave movement
- Rayleigh waves: this causes the surface rocks to have a vertical circular movement.