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7 questions · timed · auto-graded

Question 13 Marks
Name the causes of earthquakes.
Answer
  1. Volcanic eruptions
  2. Faulting
  3. Elasticity of rocks
  4. Local causes
  5. Apeiron, Genetic events.
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Question 23 Marks
Describe the main type of Earthquake Waves.
Answer
Earthquake Waves:- Earthquake waves travel in all directions from the Focus. There are three types of earthquake waves :
  1. Longitudinal Waves: These are known as Primary Waves ‘P’
  2. Transverse Waves: These are known as Secondary Waves ‘S’.
  3. Surface Waves: These are called Long Waves or ‘L’ Waves.
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Question 33 Marks
What was the cause of the Koyna earthquake in India?
Answer
Koyna Dam is located in Maharashtra on the Deccan plateau. This part was considered a stable block free from earthquakes. But the Koyna earthquake in 1986 was a big surprise. In the reservoir of the dam water gathered was more than its capacity. It disturbed the local isostatic balance. It caused an earthquake and caused cracks in the rocks. It may be called a man-made earthquake.
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Question 43 Marks
How an earthquake is caused?
Answer
Causes The chief known causes of earthquakes are believed to be as follows :
  1. When a dormant volcano erupts into activity or an active volcano discharges matter with greater violence the surrounding areas feel tremors or earthquakes.
  2. When the interior of the earth cools and contracts the outer crust in some places cracks and faults are caused. This movement causes an earthquake.
  3. Some time water percolates so deep down into the earth that it turns into steam on account of the internal heat. This steam expands and tries to force its way out. This pressure causes an earthquake.
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Question 53 Marks
How are earthquakes distributed over the globe?
Answer
The earthquakes are common along the weak tectonic belts affected by continuous tremors due to the movement of plates one upon another. Main belts are Circum-Pacific Mountain belt and Mid-World Mountain belt of fold mountains which are still in the process of upthrust forces increasing their height.
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Question 73 Marks
Describe how earthquakes are caused on the surface of the earth.
Answer
When the earth’s crust is unable to accommodate itself to the strain due to isostatic imbalance, so sudden release of energy results in violent shock or an earthquake. The earthquakes are caused by the severe tectonic movement of plates, volcanic eruption forces and isostatic imbalance often taking place due to diastrophism creating ups and downs in landform construction.
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[3 Mark Question Answer] - Geography STD 9 Questions - Vidyadip