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ICSE-IX-Geography

08: Earthquakes

with Solutions -

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    Section : I
    Fill in the blanks below
  • Qstn #1
    Most earthquakes occur on account of the strain in the .
    Ans : Most earthquakes occur on account of the strain in the
    earth’s crust.
  • Qstn #2
    are the first earthquake waves to be recorded on a seismograph of an earthquake.
    Ans : P (primary or push waves) are the first earthquake waves to be recorded on a seismograph of an earthquake.
  • Qstn #3
    The last of the earthquake waves to arrive on the surface of the earth are waves.
    Ans : The last of the earthquake waves to arrive on the surface of the earth are
    L (surface or long) waves.
  • Qstn #4
    The giant sea waves caused by earthquakes in the oceans are called .
    Ans : The giant sea waves caused by earthquakes in the oceans are called
    Tsunamis.
  • Qstn #5
    About 70 per cent of the earthquakes occur in the Belt.
    Ans : About 70 per cent of the earthquakes occur in the
    Circum- Pacific Mountain Belt.
  • #
    Section : II
    Short Answer Questions
  • Qstn #1
    What is called an earthquake ?
    Ans : An earthquake is defined as a tremor below the surface of the earth which causes shaking of the earth.
  • Qstn #2
    State two natural causes of an earthquake.
    Ans : Natural causes are the movement of tectonic plates and volcanic activities.
  • Qstn #3
    Name one man-made cause of an earthquake.
    Ans : Construction of large scale dams, thrust of rivers along fault lines, dumping of chemical wastes also cause earthquakes due to imbalance in isostatic balance of the earth’s landforms, e.g. Koyna dam caused an earthquake in Maharashtra.
  • Qstn #4
    What are known as seismic focus and epiceptre with respect to an earthquake ?
    Ans : The point of origin of earthquake waves is called seismic focus and the centre vertically above the seismic focus nearest to the earth’s crust is called epicentre.
  • Qstn #5
    What is known as Richter scale ? State its uses.
    Ans : Ritcher scale is used to measure the intensity of earthquake through a scale, which is motivated by a needle attached to this instrument The zigzag wavelength of the earthquake comes on the screen and calculated from 1 to 9 scale measured in centimetres.
  • Qstn #6
    How are earthquakes useful ?
    Ans : Earthquakes cause energy release to put the earth in good shape; several landforms are uplifted to build large plains e.g. Sagami Bay uplifted 200 m, Landslides cause the formation of lakes in Himalayan region.
  • Qstn #7
    Give any two destructive effects of earthquakes ?
    Ans : Destructive effects are collapse of structures, submergence of coastal parts e.g. Dwarka submergence, these change the course of rivers, danger to human life and motivation of tsunami waves causing drastic calamities.
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