How many seismic and tide stations are used by ITWS?
What
happens when a major earthquake or other disturbance prompts a tsunami?
How
does the International Tsunami Warning System Work?
How are watches and warnings disseminated?
What
are the Capabilities and Limitations of the International Tsunami
Warning
System (ITWS)?
What is a seismic
station?
A seismic station is a laboratory
that has equipment that can detect,
monitor and record earthquakes locally or anywhere
in the world. It has
different type of seismic instruments that can
record earthquake waves
traveling trough the interior of the earth and
its surface. A functioning
seismic station must be able to perform many
different functions and
determine important parameters of an earthquake
such as magnitude, depth,
and epicenter.It must have the ability to communicate
effectively with other
seismic stations and to share data.
What
is a tide station?
A tide station has one or
more calibrated instruments, called tide gauges,
which have the ability to measure long and short
term changes in sea level
from astronomical tides or long period waves
such as tsunami waves of
surges. Tide stations in the ITWS telemeter their
data via satellite to PTWC
and other regional warning centers.
How
many seismic and tide stations are used by ITWS?
The International Tsunami
Warning System makes use of an extensive seismic
and tide gauge network. However, it makes primary
use of 31 seismic
stations, and more than sixty tide stations which
have the ability to
transmit their data immediately and in real time
to the headquarters at the
Pacific Tsunami Warning Center in Hawaii.
What
happens when a major earthquake or other disturbance prompts a tsunami?
How does the International Tsunami Warning
System Work?
Functioning of the System
begins with the detection of an earthquake which
has a magnitude and location that make it potentially
capable of generating
a tsunami. The earthquake has to be of sufficient
magnitude to trigger the
alarm attached to the seismograph at the station
where it is being recorded.
The alarm thresholds are set so that ground vibrations
of the amplitude and
duration associated with an earthquake of approximate
magnitude 6.5 or
greater on the Richter Scale anywhere in the
Pacific region will cause them
to sound. Personnel at the station immediately
interpret their seismographs
and send their readings to the Pacific Tsunami
Warning Center (PTWC)., in
Honolulu, which are the headquarters for the
international system (ITWS).
Upon receipt of a report from one of the participating
seismic observatories
or as a consequence of the triggering of their
own seismic alarm, PTWC
personnel send messages requesting data from
the observatories in the
system.
How
are watches and warnings disseminated?
When sufficient data has been
received so that the earthquake can be located
and the magnitude computed, a decision is made
as to further action. If the
earthquake is strong enough to cause a tsunami
and is located in an area
where this is possible, participating tide stations
near the epicenter are
requested to monitor their tide gauges. Watch
bulletins are issued to the
dissemination agencies for all earthquakes of
magnitude 7 or greater
occurring in the Aleutian Islands and all earthquakes
of magnitude 7.5 or
greater occurring elsewhere in the Pacific. A
watch may also be disseminated
by PTWC upon the issuance of warnings by the
regional warning centers. Since
the regional systems use different criteria for
their disseminations, a
watch may at times be issued for earthquakes
with magnitude less than 7.5.
When reports from tide stations
show that a tsunami poses a threat to the
population in a part or all of the Pacific, a
warning is transmitted to the
dissemination agencies for relay to the public.
These agencies then
implement plans to evacuate people from endangered
areas. If the tide
station reports indicate that either a negligible
tsunami or no tsunami has
been generated, PTWC issues a cancellation.
Tsunami watches and warnings
are disseminated by PTWC to over 100
dissemination points scattered throughout the
Pacific Basin under the
varying control of the member states with general
guidance from IOC, and the
ICG/ITSU. These major dissemination points are
responsible for further
dissemination to hundreds of other points within
their geographical
jurisdictions.
The major dissemination responsibility
of the ITWS is the tsunami watch
and/or warning. The dissemination program is
a sophisticated cooperative
venture using existing national and international
communication facilities.
The communications systems to over 100 dissemination
points along with over
100 data gathering stations are tested monthly
with dummy messages. The
tests are monitored for minimum message travel
times. These dissemination
points in turn disseminate to many more points
in their respective local
areas. ITIC has played a significant role in
coordinating cooperation among
nations in the ITWS and establishing communication
requirements, procedures,
and monitoring the results.
What
are the Capabilities and Limitations of the International Tsunami
Warning System (ITWS)?
A tsunami originates in or
near the epicentral area of the earthquake that
creates it. It propagates outward in all directions
at a speed that depends
on ocean depths. In the deep ocean the speed
may exceed 600 km/s; thus, the
need for rapid data handling and communication
becomes obvious. Because of
the time spent in collecting seismic and tidal
data, the warnings issued by
PTWC and ATWC (headquarters for international
warnings) cannot protect areas
against local tsunamis in the first hour after
generation; for this purpose,
regional warning systems have been established
in some areas.
The regional systems generally
have data from a number of seismic and tide
stations telemetered to a central headquarters.
Nearby earthquakes are
located, usually in 15 minutes or less, and a
warning based on seismological
evidence is released to the population of the
area. Since the warning is
issued on the basis of seismic data alone, watches
or even warnings will
occasionally be issued when tsunamis have not
been generated. Since they are
issued only to restricted area and confirmation
of the existence or
nonexistence of a tsunami is rapidly obtained,
dislocations of populations
are minimized. To limit the number of agencies
to be contacted, warnings are
generally issued to only one agency in each country,
territory, or
administrative area.
Dissemination agencies have
the continuing responsibility for educating the
public concerning the dangers of tsunamis and
for developing safety measures
that must be taken to avoid loss of life and
to reduce property damage. The
agencies are encouraged to develop emergency
plans for all threatened
localities, clearly delineating areas of possible
inundation. Evacuation
routes are designated, safe areas marked, and
the amount of advance warning
to insure evacuation from danger
Information from The Tsunami Page- Dr. George P.C.