Transcript Earthquake Prediction

The specification notes that you must be
able to describe methods of earthquake
prediction.
You must also understand the social
consequences of earthquake prediction.
You must be able to describe the measures
designed to reduce the impact of
earthquakes.
Throughout history,
people have attempted
to predict earthquakes .
seismologists have been
working toward a goal to
make earthquake
forecasting about as
reliable as weather
forecasting.
They aim to predict not
only the date and
location of a quake, but
also the intensity.
Seismic Gap Theory
The ``seismic gap''
theory postulates that
over the long run all
parts of the fault must
average about the same
level of movement per
time.
A large and longstanding
``seismic gap'' is usually
interpreted to mean that
a significant earthquake
should be expected.
Detailed Measurements of gases
Increased Fluctuation in
Radon (and helium) Gas
Emission
Deep wells have been noted
to experience an increase in
the release of radon gas in
the area around a
forthcoming earthquake.
However, this data is scarce
and it is not known if it is a
clue to coming quakes or just
a normal occurrence, not
related to seismicity.
Stress in Rocks
Stress builds up in the
rocks adjacent to an active
fault.
This will continue to build
until the fault ruptures and
the energy is released.
Strain gauges are used to
monitor the build up of
stress and so indicate when
an earthquake may happen.
However, it cannot predict
an accurate date and time.
Water Levels
It has been noted that groundwater
levels do rise very shortly before an
earthquake.
However, this does not always happen
and it gives little warning.
Ground levels
As stress builds up along a
fault, the ground level can
change.
The ground often tilts or
rises in the area of a coming
earthquake.
Unfortunately, many
processes cause the ground
surface to rise or tilt which
makes this technique
difficult to use as a
predicting tool.
However, this method has
been useful in Japan
Changes in P Wave Velocity
It is thought that the properties of rocks
change before an earthquake and so the
velocity at which various earthquake waves
travel through them might change as well.
It has been noticed that the P-wave velocity
changed by about 10%-15% before
earthquakes.
The velocity decreases for a while, then
increases back to normal just before the
main shock...at least sometimes.
These measurements are very easy to make
because the velocity of earthquake waves are
precisely what seismometers are built to
measure.
Changes in Electrical Conductivity
The electrical conductivity of rocks in the
area around earthquakes has been known to
change just before shocks.
The methods success is encouraging
because lab results are consistent for
almost everyone who performs
experiments.
This could be a very helpful clue to
forecasting earthquakes.
Patterns of Foreshocks and Aftershocks
In terms of prediction research, the most
effort has been put into studying variation in
seismicity rate.
But, all of the studying has not produced a
definite answer.
Seismologists study the pattern of aftershocks
and foreshocks.
In Italy, China, and California, earthquakes
have been successfully predicted using a
noticed increase in background seismic activity.
Tiny shocks increase in number and magnitude
leading up to a large shock.
If these foreshocks can be recognized as such
in enough time to warn people in the necessary
areas, many lives can be saved.
Strange animal behaviour
Examples include an intense
fear that appears to make
some animals cry and bark
for hours, and others flee in
panic.
Equally characteristic is the
apparent opposite effect of
wild animals appearing
confused, disoriented, and
losing their usual fear of
people.
Some other common
observations are that
animals appear agitated,
excited, nervous, overly
aggressive, or seem to be
trying to burrow or hide.
Animal behaviour and Haicheng
On February 4, 1975 the Chinese successfully
evacuated the city of Haicheng several hours
before a 7.3 magnitude earthquake-- based
primarily on observations of unusual animal
behaviour.
90% of the city's structures were destroyed in
the quake, but the entire city had been
evacuated before it struck.
Nearly 90,000 lives were saved.
Since then China has also had some false
alarms, so their system is certainly not foolproof.