Sequence of events in an Earthquake
in both the natural and cultural environment
NATURAL ENVIRONMENT
CULTURAL ENVIRONMENT
Before the earthquake
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Molten rock ( magma ) rises to the Earth’s crust
as a result of convection currents in the mantle.
This leads to the movement of the tectonic
plates. Friction builds up as the plates move apart,
come together or move past each other.
Days or weeks may occur before a major
earthquake or earthquakes occur. There are often
many little shocks, or tremors, that occur called
foreshocks. They are the result of pressure
building the tectonic plates.
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Emergency procedures have been planned eg Civil
Defence
People go about their every day activities such as
work, leisure etc
People may detect foreshocks and be alarmed by
them
During the earthquake
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A sudden jerking movement between two plates
will result in severe movement of the ground
above. This shaking generally lasts for less than
40 seconds.
Primary waves radiate in all directions from the
focus on the earthquake.
There are three different types of seismic waves:
P waves, S waves and L waves. P waves (primary
waves) travel rapidly. They are sound waves and
can move through solids, liquids and gases.
Although they are the first waves recorded by
instruments they do very little. S waves
(secondary) can be very destructive. An S wave
only travels through solid material. These waves
cause the ground to shake violently both vertically
and horizontally. L waves (long waves) are slower
than p waves and s waves, but they can also be
very destructive.
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Panic
People may be injured or killed
Buildings can collapse, people’s property can be
damaged or destroyed.
Infrastructure may be damaged eg
communication systems may be disrupted; cracks
or fissures may damage roads and railroads;
bridges may collapse; gas and electricity lines may
be cut.
After the earthquake
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The major earthquake is usually followed by
aftershocks.
These are earthquakes of a smaller magnitude.
These aftershocks can be strong enough to cause
further destruction.
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Emergency services respond.
Rescue teams try to save trapped people in the
following days. Unsafe areas are evacuated and a
state of emergency may be declared.
People begin the clean up process, such as clearing
debris.
Aid supplied to homeless people.
Medical supplies distributed and treatment
provided to the injured.
Water and sewerage systems (also
communication) returned to normal.
Weeks and years after the earthquake
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Tectonic processes continue to operate below the
surface of the earth creating the potential for
earthquakes to occur again.
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Rebuilding of buildings, roads and services.
Emergency systems are reviewed and where
necessary improved.
Research is conducted to improve building
structures in order to reduce future earthquake
damage eg the invention of lead rubber bearings
to stabilize buildings.
Continued research into the detection of
earthquakes so that people can be warned.
People in the area go back to their normal lives.