An earthquake is the shaking and vibration at the
surface of the Earth caused by energy being
released along a fault plane, at the edge of a tectonic
plate or by volcanic activity.
Earthquakes are caused by the movement of Earth’s
outer layer (the crust and a portion of the upper
mantle). The outside layer of Earth is split into
tectonic plates which are moving slightly due to the
movement of magma in the layer below. This causes
plates to squeeze together, move apart and slide
alongside each other.
Earthquakes are classified into two types:
..Interplate earthquakes – these earthquakes occur
on tectonic plate boundaries where the tectonic
plates are moving towards each other or sliding
alongside each other. Interplate earthquakes are
common for countries such as Japan, New Zealand
and the west coast of the United States which are
located on tectonic plate boundaries. Large
earthquakes are usually interplate earthquakes.
..Intraplate earthquakes – these earthquakes occur
in the middle of tectonic plates on fault zones
where the pressure of the tectonic plate being
squashed and forced to move builds up and is
released through the cracks in rocks associated
with fault zones, resulting in an earthquake. As
Australia is located in the middle of a tectonic plate,
we are less susceptible to larger earthquakes;
however damaging earthquakes can still occur on
fault zones.
This
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Earthquakes involve the powerful movement of rocks in the
Earth’s crust. The rapid release of energy creates seismic
waves that travel through the earth.
Scientists use the different speeds of seismic waves to locate
the epicentre (the point on the surface directly above where
the earthquake originated) of earthquakes.
Seismometers are used to measure the magnitude of
earthquakes. You are unlikely to feel a magnitude 3 earthquake
but a magnitude 6 earthquake could potentially cause large
damage.
The damage caused by earthquakes also depends on their
depth and fault type.
The earthquake that hit the Tohoku region of Japan on March
11, 2011, had a magnitude of 9.0 and killed over 15000 people.
The destruction caused by the Tohoku earthquake was made
much worse by powerful tsunamis that were triggered due to
the earthquake’s epicentre being located offshore. More
tsunami facts.
The 2004 earthquake that occurred in the Indian Ocean near
Sumatra, Indonesia triggered a series of tsunamis that killed
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over 200000 people in 14 countries.
The February 2011 earthquake in Christchurch, New Zealand
followed nearly 6 months after a magnitude 7.1 earthquake
shook the region. The earthquake killed 181 people and
significantly damaged the central city. The economic damage
caused by the earthquake and aftershocks is estimated to be
around $15 billion (NZ$).
An earthquake that hit Haiti in January 2010 with a magnitude
of 7.0 killed over 200000 people according to Haitian sources.
The most powerful earthquake ever recorded on Earth was in
Valdivia, Chile. Occurring in 1960, it had a magnitude of 9.5.
It is important in earthquake prone countries such as Japan to
build houses and buildings that react well to earthquakes. Good
engineering practises can help stop buildings collapsing under
the stress of large earthquakes.