Earthquakes and Tsunamis
The Earth is made up of a boiling hot, liquid centre covered by
a crust. This crust is broken into pieces called tectonic plates,
which move around, sometimes colliding into each other. These
collisions lead to earthquakes, some so small that they are hardly
felt. But some earthquakes are so massive that they cause the
ground to shake violently, destroying houses and killing people.
Quick Q’s:
1. Which is the worst
earthquake in history?
In 1556, an earthquake
struck three provinces
in China. About
830,000 people were
killed in the disaster.
It was the worst
earthquake in history.
2. Can we predict
earthquakes?
No, we cannot. The
movements of the
Earth are too complex
for us to be able to
predict earthquakes.
But we do know the
lines along which the
Earth’s plates meet,
so we know the areas
that are more likely
to have earthquakes.
3. What is liquefaction?
Liquefaction is caused
by the violent shaking
of the ground during
an earthquake. Moist
soil or sand turns into
slurry, like quicksand.
This liquid can suck in
entire buildings.
4. Is a tsunami the
same as a tidal wave?
A tsunami is diffeerent
from a tidal wave.
A tidal wave is
generated by high
winds, but a tsunami is
caused by underwater
earthquakes, landslides
or volcanic eruptions.
Q Do earthquakes occur everywhere?
A Earthquakes usually occur along a region
called a fault, where broken rocks under the
Earth’s surface rub against each other and
cause tremors. Faults are marked by cracks on
the Earth’s surface, caused by the movement
of tectonic plates. Most faults are located near
the edges of the plates, but small faults can be
found far away from the boundaries.
Q How do faults produce earthquakes?
A Faults allow the rock fragments that form
the Earth’s crust to move about. Over a
period of time, plate movement builds up
pressure, causing rocks along a fault to bend
or break with a jolt. This sudden movement
releases energy that moves through the surface
of the Earth in the form of waves. This is an
earthquake. The energy moves out in a circle
from the point where the movement occurs.
38
Fault in the Earth
The San Andreas Fault in
California, USA, is one
of the few faults in the
Earth’s surface that can
actually be seen by any
observer on the ground.
Most of the other faults
are covered by soil or
water. These faults mark
the lines on the Earth’s
surface where two
tectonic plates of the
Earth meet. As a result,
areas around these faults
are the ones most prone
to volcanic activity
and earthquakes.
San Francisco 1906
The notorious San
Francisco earthquake
in 1906 destroyed
most of the large
buildings in the
city. Tramlines
were ripped up
as the roads
buckled
under
them.
Earthquakes and Tsunamis
Q Where is an earthquake most dangerous?
A The point inside the Earth where the
rocks first begin to break is the focus of the
earthquake. The point on the Earth’s surface
that lies directly above the focus is called
the ‘epicentre’. This is where the earthquake
is strongest. In a major earthquake, the
maximum damage takes place at the
epicentre, and there is less damage as you
get further away from it. The epicentre is
directly above the hypocentre, the actual
location of the energy released inside the
Earth. Seismic waves ripple out from the
hypocentre. After an earthquake, scientists
can find the centre by looking at the seismic
wave data from three separate locations.
The extent of the damage caused by an
earthquake may also depend on the
nature of the soil.
ليست هناك تعليقات:
إرسال تعليق