One of the most common hazards inflicting
tremendous damage to human life and material
properties is an earthquake. It is a natural
phenomenon that poses great danger due to
various hazards it may bring. Though is
impending occurence can be predicted the
magnitude of its impact to a community and its
people
is
unpredictable.
This
makes
earthquake one of the main foci of disaster
preparedness and emergency response
activities of governments and different
emergency agencies.
An earthquake (also known as a quake,
tremor or temblor) is the perceptible
shaking of the Earth, resulting from the
sudden release of energy in the Earth’s
crust that creates seismic waves. (US
Geological Science – USGS)
Geologists explain that an earthquake is a
type of hazard that depends on the
strength of seismic activity, along with
such factors as local topographic and built
features,
subsurface
geology
and
groundwater. A large earthquake will
always be followed by a sequence of
aftershocks that normally aggravates its
effect on human and material elements
like buildings and infastructure.
The Earth shakes with the passage of
earthquake waves, which rediate
energy that had been “stored” in
stressed rocks, and were released
when a fault broke and the rocks
slipped to relieve the pent-up stress.
The strenght of ground shaking is
measured in the velocity of ground
motion, the acceleration of ground
motion, the frequency content of the
shaking and how long this shaking
continues (the “duration”).
Surface rupture is an offset of
the ground surface when fault
rupture extends to the Earth’s
surface. Any structure built
across the fault is at risk of
being torn apart as the two
slides of the fault slip past each
other.
Soil liquefaction is a
phenomenon in which the
strenght and stiffness of a soil is
reduced by earthquake shaking
or other rapid loading. It normally
occurs in saturated soils, that is,
soils in which the space between
individual particles is completely
filled wuth water.
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