Current Affairs

# How Does The Earthquakes and Tsunami Occurred?

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.

Where do earthquakes occur?
Earthquakes occur mainly at the borders of the plates (see the figure on page 14), where two plates slide past each other. Most earthquakes occur in the Himalayan region. The actual seismic centre, the ‘hypocentre’ es 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 this point. They measure the time it takes the shock waves to reach the siesmic 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 of the Earth’s surface with’s 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 the earthquakes. A pen is attached to this pendulum. hen the Earth trembles, the surface of Earth, together with the paper placed there, moves to and from 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 tensity of 8.o are very destructive.

What damages can earthquakes cause?
A weak earthquake 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 catastrophes, bridges, dams, and power plants get damaged-and often whole areas are devastated.

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, 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.

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, A 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 kilometre in thickness above it moves with it. The wave caused by this movement has a loof energy-much more than a wave of the same height whipped up by the wind.

Did you know that
about 10, ooo earthquakes occur every year, of which only a few cause damages?
in December 20o4, around 230, ooo 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 behavevstrangely or flee before an earthquake? They seem to sense something, which we cannot experience

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