2. What is an earthquake?
An earthquake is what happens when two blocks of the earth
suddenly slip past one another. The surface where they slip
is called the fault. The location below the earth’s surface
where the earthquake starts is called the focus, and the
location directly above it on the surface of the earth is
called the epicenter.
Earthquakes are sudden, violent shaking of the earth’s
surface. They occur after a build-up of pressure causes rocks
and other materials to give way.
3. Earthquake measurement
There are two ways by which we can measure the strength of
an earthquake: magnitude and intensity. Magnitude is
proportional to the energy released by an earthquake at the
focus. It is calculated from earthquakes recorded by an
instrument called seismograph. It is represented by Numbers
(e.g. 5.8, 9.0). Intensity on the other hand, is the strength of
an earthquake felt by people in a certain locality. It is a
numerical rating based on the relative effects to people,
objects, environment, and structures in the surrounding.
The intensity is generally higher near the epicenter.
4. Types of earthquake
There are two types of earthquakes: tectonic
and volcanic earthquakes. Tectonic
earthquakes are produced by sudden
movement along faults and plate boundaries.
Earthquakes are by rising lava or magma
beneath active volcanoes is called volcanic
earthquakes.
5. What Causes Earthquakes
Earthquakes are the result of slow-moving processes
that operate within Earth.
Earth was hot when it formed, and has been cooling
ever since (near the surface, for each km into Earth,
the temperature rises by about 30deg. Celsius).
Earth's cooling causes the portions of Earth to move,
and that movement is what we call an earthquake.
6. The earth has four major layers: the inner core, outer
core, mantle and crust. The crust and the top of the
mantle make up a thin skin on the surface of our planet.
But this skin is not all in one piece – it is made up of many
pieces like a puzzle covering the surface of the earth. Not
only that, but these puzzle pieces keep slowly moving
around, sliding past one another and bumping into each
other. We call these puzzle pieces tectonic plates, and
the edges of the plates are called the plate boundaries.
The plate boundaries are made up of many faults, and
most of the earthquakes around the world occur on these
faults.
7. Some earthquakes are caused by human
activities such as:
Nuclear testing
Building large dams
Drilling for oil
Coal mining
8. Earthquake damage
The extent of earthquake damage is influenced by a number
of factors:
Strength of earthquake and number of aftershocks – the
stronger the earthquake the more damage it can do. For
example an earthquake of 6.0 Richter scale is 100 times
more powerful than one of 4.0; the more aftershocks there
are the greater the damage that is done.
Population density: an earthquake that hits an area of high
population density, such as in the Tokyo region of Japan,
could cause far more damage than one hits an area of low
population and low building density.
9. The type of buildings- MEDCs generally have better quality
buildings, more emergency services and the funds to cope with
disasters.
The time of day – an earthquake during a busy time, such as
rush, hour may cause more deaths than one quiet time.
The distance from the centre (epicenter) of the earthquake –
the closer a place is to the center of the earthquake , the
greater the damage that is done.
The types of rocks: loose materials may act like liquid when
shaken, solid rock is much safer and buildings should be built on
level areas formed of solid rock.
Secondary hazards: such as mudslide and tsunamis (large sea
waves), fires contaminated water, disease, hunger, etc.
