International Tsunami Warning System

What is 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.

What is a WDC?

A WDC is the acronym for a World Data Center.