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  • Why does the Earth tremble sometimes?

    Why does the Earth tremble sometimes?

    Why does the Earth tremble sometimes?

    The moving tectonic plates, in which the uppermost layer of the Earth is divided, not only collide at many places but also often slide past each other. This causes friction and leads to problems once in a while. Stress builds up, which then gets discharged very quickly. There is a jerk—the Earth trembles. This gives rise to shock waves that can cause a lot of damage at places, depending on the intensity of the earthquake and where they occur. Luckily, to some extent we can protect ourselves from these waves. A tsunami occurs if the centre of the earthquake lies below the sea.


    seismograph

    Where do earthquakes occur?

    Earthquakes occur mainly at the borders of the plates (see in the last post), where two plates slide past each other. Most earthquakes occur in the Himalayan region. The actual seismic centre, the 'hypocentre', lies deep below the surface of the Earth. The point on the surface of the Earth lying immediately above this is called the 'epicentre'. Scientists can determine the point. They measure the time it takes the shock waves to reach the seismic stations and draw circles around the epicentre and two other seismic stations.

    The radius of these circles corresponds to the measured time. The point of intersection is the epicentre. Right below the epicentre, beneath the Earth's surface, lies the hypocentre.


    How do we measure the intensity of earthquakes?

    The intensity of an earthquake is measured by recording the tremors of the Earth's surface with a 'seismograph'. These tremors appear when the earthquake waves reach the surface of the Earth. Such a seismograph consists of a large, inert weight, which stays at rest even during earthquakes. A pen is attached to this pendulum. When the Earth trembles, the surface of the Earth, together with the paper placed their, moves to and fro below the 'writing pendulum' which does not move. We can then detect the different types of waves on the paper, which move at different speeds. The intensity of the earthquake can be calculated from these wave patterns. The intensity is measured on a scale, called 'Richter scale', named after its inventor. Earthquakes with an intensity of 2.5 can be felt, but ones with an intensity of 8.o are very destructive


    What damages can earthquakes cause?

    A weak earthquake-up to an intensity of 4.0 on the Richter scale-hardly causes any damage. Earthquakes with stronger intensities can cause cracks in buildings. They move the foundations of buildings, cause houses to collapse, and lead to landslides. Supply lines get disrupted and gas leakage causes fires. In large earthquake catastrophe, bridges, dams, and power plants get damaged-and often whole areas are devastated.


    plates

    How do we save ourselves from earthquakes?

    Living in an earthquake-prone zone is often unavoidable. For instance, almost entire Japan lies in an earthquake-prone zone. For this reason, Living in an earthquake-prone zone is often unavoidable. For instance, almost entire Japan lies in an earthquake-prone zone. For this reason,buildings here are primarily made 'earthquake resistant' so that the loss can be minimized. Buildings are built on foundations made of steel balls or from elastic materials such as bamboo. In skyscrapers, a pendulum weighing several tons is installed in the upper floors, which minimizes the vibrations that start in the upper storeys when an earthquake occurs. If an earthquake occurs, we should take refuge, at best, in the open or seek protection under a table.




  • about 10,000 earthquakes occur every year, of which only a few cause damages?
  • in December 2004, around 230,000 people died in a devastating tsunami?
  • most of the tsunamis do not cause any damage, as they occur in the sparsely populated Pacific area?
  • animals often behave strangely or flee before an earthquake? They seem to sense something, which we cannot experience

  • How does a tsunami occur?

    The Japanese word 'tsunami' means 'harbour wave'. It is a series of water waves caused by the displacement of a large volume of a body of water, usually an ocean, though it can occur in large lakes. Tsunamis are caused by undersea landslides or by 'seaquakes', that is an earthquake whose epicentre lies below the ocean. If the seabed is displaced up to several metres, the water layer of several kilometres in thickness above it also moves with it. The wave caused by this movement has a lot of energy-much more than a wave of the same height whipped up by the wind.This becomes apparent when the wave moves towards the coast.


    tremble


    Artificial earthquake

    You need: Dominoes, a large and a small flat board, an eraser
    Do as follows: Place the dominoes one above the other on the large board. Position the small board in such as way that it touches the larger board. Now, press the smaller board against the larger one and at the same time move it backwards. Repeat the activity replacing the small board with the eraser.