Little evidences of vertical or horizontal movement

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- Little evidences of vertical or horizontal movement but with evidences of close warping of few minor faults (ii) Semi-mobile region - Characterised by differential vertical movement and formation of Sedimentary basin (iii) Mobile belts - Characterised by young mountain ranges - Strong deformation - Strong vertical and horizontal movements Oceanic crusts are mostly basalts and Gabbro, 5 – 11 km thick and they mostly exist in three layers namely: (i) Layer 1 - It is a non consolidated sediment - It has seismic velocity of between 1.5 – 1.8 km/s - It is 0.3 to 0.8 km thick (ii) Layer 2 - It is 1 – 2 km thick - It has seismic velocity of 2.1 – 5.5 km/s (iii) Layer 3 - It is a basaltic layer - It has seismic velocity of between 6.5 and 7.0 km/s
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- 35 - - It is 5 km thick (b) Mohorovicic Boundary: It is chemical boundary separating silicic crustal rock with high Feldspar content from underlying Ultramafic rocks of mantle. (c) Mantle: It is a solid layer and is about 2900 km thick. It is the largest of all the subdivisions, 84% by volume and 69% mass of the entire earth and divided into 3 zones namely: (i) Upper mantle - Mineralization of upper mantle is approximately 40% Olivine, 50% Pyroxene and 10% Garnet (ii) Transition layer - It is characterised by abrupt increase in seismic velocity which is attributed to phase change - It is iron rich (iii) Lower Mantle - Seismic velocity and density increase steadily with depth - It has velocity homogeneity (b) Gutenberg Boundary: It is a discontinuity between the mantle an the core (c) Core: It is 16% and 13% by volume and mass of the earth. It is about 3470 km thick extended to the centre of the earth and is in 3 zones namely: (1) Outer core - It is about 2080 km thick
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- 36 - - It is believed to be in liquid form because seismic S – Wave cannot pass through it - Earth’s magnetic field originates from it - The response of the earth to tidal forces which affects axis of rotation and the centrifugal force that counter the centripetal force along the equator, which is responsible for the bulginess of the earth at the equator, are associated with the liquid nature of the outer core (ii) Transition zone It is a slightly rigid shell (140 km thick) surrounding the solid inner core with temperature of about 3000 kelvins which is about the melting point of iron. (iii) Inner core It is 1250 km thick, solid and with P – wave velocity increase inward, which implies density increase. 3.2.2 Earth’s Model based on Ability to flow Earth model can be drawn based on the ability of its layer to flow. The layers are: 1 Lithosphere- cold and brittle. flow to capable re Rheonosphe ere Asthonosph 3 2 It was reported that towards the centre it becomes hardened again as a result of pressure. 3.3 Self – Assessment exercise 1
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- 37 - (i) What is the source of the centrifugal force that is responsible for the bulginess of the earth?
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