Emergency Dispatch Vol 4 2014

20
Earthquake
Survival
Earthquakes are a shaking or trembling of the
Earth’s crust caused by the release of huge
stresses due to underground volcanic forces,
the breaking of rock beneath the surface, or by
sudden movement along an existing fault line.
The latter type results from constant gradual
movement of the tectonic plates that make up
Earth’s crust, which causes stress to build up
in rock layers. Small earthquakes sometimes
result from human activity (e.g. filling of large
reservoirs).
Characteristics and Measurement
Earthquakes are unpredictable and strike without
warning. They range in strength from slight
tremors to great shocks lasting from a few
seconds to as long as five minutes. They can
occur in a series over a period of several days.
Energy released by (or magnitude of) an
earthquake is recorded on a seismograph, using
the Richter scale. This scale is open ended, as
there is no upper limit to the amount of energy
an earthquake might release. The most severe
earthquakes so far have not exceeded 9.5 on
this scale. It is not a simple arithmetic scale; for
instance, a magnitude 7.0 earthquake creates
10 times the ground motion of a magnitude 6.0
earthquake and the total energy release is about
30 times greater. This, in turn, is 30 times greater
than a magnitude 5.0 earthquake and so on.
Another scale used to describe earthquakes is
the Modified Mercalli (MM). It rates the amount
of shaking felt and damage caused (or intensity),
and uses Roman numerals. On this scale,
I is a barely detectable tremor, and XII is total
damage.
Causes of Injury & Damage
Most earthquake casualties result from falling
objects or debris when shocks damage or
demolish buildings and other structures.
Electricity and telephone lines, and gas, sewer
and
water mains can be damaged;
landslides, ground displacement (faulting),
subsidence and tsunamis may result, leaving
many people dead, injured or homeless.
Newcastle University Library / 1989