Earthquakes
16 Grade 10 Geography questions on Earthquakes, with worked marking schemes. 16 questions are available on this topic in full.
Question 1
1 markA Grade 10 class in Nakuru is told that a tremor was recorded with a magnitude of 4.2 on the Richter scale. What does the magnitude of an earthquake measure?
A. The number of aftershocks that follow the main tremor
B. The amount of damage caused to buildings and roads
C. The depth of the focus below the earth's surface
D. The amount of energy released by the earthquake
(1 mark)
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1 markA seismologist wishes to fix the exact position of the epicentre of an earthquake. What is the minimum number of recording stations required?
A. Two stations
B. Six stations
C. One station
D. Three stations
(1 mark)
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4 marksAccount for the fact that an earthquake of moderate magnitude may cause very little damage in one place but severe damage in another.
(4 marks)
Marking scheme
Any four, 1 mark each (4 marks): - Depth of focus: a shallow focus releases energy close to the surface and shakes it violently, while a deep focus loses energy before the waves reach the surface. - Distance from the epicentre: damage decreases as distance from the epicentre increases because the waves weaken outwards. - Nature of the underlying rocks: soft, water-logged sediments and reclaimed ground amplify shaking, while solid bedrock shakes less. - Population density and level of development: a built-up town has more structures and people to be affected than sparsely settled grazing land. - Quality of building construction: poorly built structures collapse easily while earthquake-resistant ones withstand the shaking. - Time of occurrence: a tremor at night or during school hours finds people indoors and raises casualties. Accept any four valid, distinct factors.
Question 4
1 markA tsunami that strikes the Kenyan coast at Malindi is most likely to be generated by an earthquake that:
A. shook the coastal sand dunes and loosened the beach sediments
B. had a very high magnitude but a very deep focus inland
C. occurred on land and caused landslides into a river
D. displaced the sea floor suddenly along a fault under the Indian Ocean
(1 mark)
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1 markWhich safety action should a learner take first when an earthquake begins while she is inside a classroom with a concrete roof?
A. Open the windows to let the shock waves pass through the room
B. Run out through the corridor to the open field immediately
C. Drop down, take cover under a desk and hold on until the shaking stops
D. Stand in the doorway of the classroom until help arrives
(1 mark)
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3 marksDescribe how a seismograph records an earthquake.
(3 marks)
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4 marksOutline four negative effects of a severe earthquake on the economy of a country.
(4 marks)
Marking scheme
Any four, 1 mark each (4 marks): - Destruction of buildings, factories and homes, leading to heavy losses and costly reconstruction. - Damage to infrastructure such as roads, railways, bridges, water pipes and power lines, which disrupts transport and trade. - Loss of life and injuries, which reduces the labour force and raises the cost of health care. - Damage to farmland, irrigation channels and livestock, which lowers food production. - Displacement of people, forcing the government to spend on relief food, shelter and resettlement. - Discouragement of investment and tourism in the affected region because of the perceived risk. Do not credit points that are purely physical with no economic link.
Question 8
1 markWhich type of seismic wave travels fastest, arrives first at a recording station and can pass through both solid rock and liquid layers?
A. Secondary (S) waves
B. Rayleigh waves
C. Love waves
D. Primary (P) waves
(1 mark)
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1 markWhich human activity is most likely to trigger earth tremors in an area that is otherwise stable?
A. Draining a swamp in order to grow rice
B. Filling a large reservoir with water behind a high dam
C. Planting trees on a bare hillside
D. Making terraces on a steep cultivated slope
(1 mark)
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1 markMost earthquakes felt in Kenya occur along the Rift Valley floor around Lake Magadi and Lake Baringo. The main reason for this is that the area:
A. lies at a high altitude above sea level
B. is a zone of crustal tension where blocks of land sink along faults
C. contains thick deposits of volcanic ash and soda
D. receives very low rainfall throughout the year
(1 mark)
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1 markSudden movement of blocks of land along a fault during a severe earthquake is most likely to form a:
A. fault scarp
B. corrie
C. ox-bow lake
D. sand dune
(1 mark)
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6 marksExplain three reasons why parts of the Kenyan Rift Valley experience earth tremors more often than the western Kenya highlands.
(6 marks)
Marking scheme
Any three explained points, 2 marks each (6 marks). Award 1 mark for the point and 1 mark for the explanation: - The Rift Valley lies along a zone of crustal tension (1), so the crust is stretching and blocks of land keep slipping along the faults, releasing energy as tremors (1). - The floor is crossed by many active fault lines (1), and movement along these lines of weakness produces frequent shaking (1). - The area has active and recently active volcanicity, for example around Longonot and Menengai (1), and the movement of magma and escaping gases beneath the surface shakes the overlying rocks (1). - Hot springs, fumaroles and geothermal activity at places such as Olkaria show shallow heat sources (1), which indicates a thin, unstable crust that adjusts easily (1). Accept any other valid, well explained reason.
Question 13
4 marksState four causes of earthquakes.
(4 marks)
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3 marksSuggest three measures that a county government in an earthquake-prone area of Kenya can take to reduce loss of life from future earthquakes.
(3 marks)
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4 marksExplain two ways in which the study of earthquakes has benefited human beings.
(4 marks)
Marking scheme
Any two explained points, 2 marks each (4 marks). Award 1 mark for the point and 1 mark for the explanation: - It has improved knowledge of the earth's interior (1), because the way P and S waves speed up, bend or fail to pass through certain layers reveals whether those layers are solid or liquid (1). - It has made early warning possible (1), since monitoring stations can detect the first faster waves and alert people before the more destructive waves arrive (1). - It has guided safer building and planning (1), because engineers use records of past shaking to design structures and to zone land away from active faults (1). - It has assisted in the search for underground resources (1), as artificial shock waves are used to locate structures likely to hold oil, gas or groundwater (1). - It has aided geothermal development (1), because mapping fault zones shows where hot rocks lie close to the surface, as at Olkaria (1). Accept any other valid, well explained benefit.
Question 16
2 marksDistinguish between the focus and the epicentre of an earthquake.
(2 marks)
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