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International Strategy for Disaster Reduction
Platform for the Promotion of Early Warning


What is tsunami?
In brief - Recent and historical tsunamis - Tsunami early warning system technique - Tsunami warning systems
- Key tsunami actors & organisations - Research projects - Further reading

Tsunami warning systems
Tsunami warning system in the Pacific

The Tsunami Warning System (TWS) in the Pacific was established in the middle of the last century after several tsunamis hit coastal regions in the Pacific causing death and major damage. The Pacific Tsunami Warning System (PTWS) is composed of 26 international Member States that are organized as the International Coordination Group for the Tsunami Warning System in the Pacific. The Group’s functions include monitoring seismological and tidal stations throughout the Pacific Basin to evaluate potential tsunami triggering earthquakes and disseminating tsunami warning information.

Seismic stations are operated by most countries, and in the USA by the following: the PTWC, the West Coast / Alaska Tsunami Warning Center (WC/ATWC), the U.S. Geological Survey's National Earthquake Information Center. If the location and magnitude of an earthquake meet the known criteria for generation of a tsunami, a tsunami warning is issued to warn of an imminent tsunami hazard. Predicted tsunami arrival times for the coastal communities which are located within the geographic area are calculated by the maximum distance the tsunami could travel in a few hours. A ‘tsunami-watch’, with further predicted tsunami arrival times, is issued for areas defined by the distance the tsunami could travel in a subsequent time period. Depending on the dimensions of the detected tsunami the warning is extended to the entire Pacific Basin. The tsunami warning is disseminated to appropriate emergency officials and the general public by a variety of communication methods. Some of these include the tsunami watch, warning and information bulletins issued by PTWC and ATWC, which are distributed to local, state, national and international users as well as to the media. These users, in turn, disseminate the tsunami information to the public, generally over commercial radio and television channels.

Additionally, the NOAA Weather Radio System, which is based on a large number of VHF transmitter sites provides direct broadcast of tsunami information to the public.

Urgent marine warnings and tsunami related information is broadcast to coastal users over medium frequency (MF) and very high frequency (VHF) marine radios by the US Coast Guard. Local authorities and emergency managers of the areas under tsunami warning are responsible to execute the existing evacuation plans. For further information on the PTWC please see NOAA’s site at:

Hawaii tsunami warning system

Hawaii is mainly affected by distant tsunamis generated throughout the Pacific Ocean. There have been only two destructive local tsunamis recorded in the last 200 years.

The following elements are included in the Hawaiian system:

  • Tsunami awareness is part of the coastal Hawaiian culture. Training to enable prompt response to tsunami warnings is conducted by local communities. These include monthly siren drills/ exercises and Emergency Alert System (EAS) radio and television broadcasts to educate the public in how to respond to emergencies including coastal evacuations.
  • Monitoring seismic activity throughout the Pacific is undertaken by the PTWC.
  • Tsunami hazard maps of the Hawaiian Islands identify areas according to their risk-levels.
  • Tsunami forecast with modern data analysis techniques aims to evacuate Hawaiian coastlines (200,000 to 300,000 residents and tourists) in a minimum of three hours prior to first wave arrival.
  • Evacuation plans are in place as a result of the coordinated effort of the PTWC, Hawaii State and County Civil Defence and the Hawaii Police Department. The evacuation plans are well understood, coordinated and exercised between the PTWC, the State, and the County. After PTWC issues a tsunami watch an initial “Prepare to Evacuate” message is issued by the State. After PTWC issues a tsunami warning, the Civil Defence authorities plan to commence a coastal evacuation. After discussion among the four groups, a decision is made to evacuate. The county administrators and the police then activate sirens and the EAS as well as authorizing Civil Air Patrol aircraft to fly over isolated coastal areas announcing evacuation. Three-minute siren signals prompt the people to turn on their radios, over which the evacuation notice is broadcast and the population is also requested to follow the evacuation instructions (evacuation maps) in the telephone book. Over 300 Sirens of various types are placed across the Islands. Most of the sirens are electronic, omni directional and non-rotating; some have voice capacity.
Japanese tsunami warning system
Japan is located near an active subduction zone experiencing many earthquakes and tsunamis. Therefore, Japan has developed one of the most extensive tsunami warning systems in the Pacific, and worldwide.

The main observatory of the Japanese Meteorological Agency (JMA) is located in Tokyo, and five regional observatories are responsible for issuing tsunami warnings. Data is continuously collected using satellites and cellular communication. After an earthquake occurs offshore, the observatories close to the epicentre will issue tsunami bulletins and tsunami warnings are broadcast within 3 minutes. The bulletins will go to the prefectures through the Local Automatic Data Editing and Switching Systems (L-ADESS), which will send forecast results like tsunami height to the main observatories. The main observatory will issue bulletins (warning, watch or information bulletin) to other prefectures and alert other government agencies through Central-ADESS. The Central Emergency Management Communication Network (CEMCN) includes ministries and agencies at the national level which contribute to disaster mitigation such as the Ministry of Construction, Tokyo Electric Power or the Nippon Broadcasting Corporation.

Stairs leading to a save place on a roof of a high building, Japan.

The following describes the local notification methods used in Japan:

  • Simultaneous Announcement Wireless System (SAWS)
    SAWS is a system of transmitters and receivers installed by local authorities for all types of messages. Transmitters are located in the local government offices and receivers are placed in hospitals, schools, fire stations, emergency management offices and other locations. Some private individuals have also bought receivers for their homes. Receiver towers with loudspeakers are installed on streets and rooftops of prominent governmental or commercial buildings. In cities, the effectiveness of SAWS is not always guaranteed because of occurrences such as bad weather when people close their windows. A device, which may be attached to telephones, can serve as a dedicated radio receiver -it will be activated by a signal from the broadcast source and will turn on the loudspeaker so that the SAWS message can then be heard.
  • Mobile Announcer System
    Fire-trucks equipped with loudspeakers cruise the areas which are not covered by the SAWS.
  • Television and Radio
    A tsunami warning is given the priority to interrupt ongoing programmes on both government and commercial television and radio stations. The message is either a subtitle on the bottom of the screen, or, a window which shows a map where the watch or warning applies; this is not possible for local tsunamis.
  • Sirens and bells
    In some villages, sirens are installed which prompt residents to turn on their radio or television for further information. Some villages still stick to tradition by clanging a bell to announce a tsunami warning.
  • Telephone network and word of mouth
    Some communities have created telephone networks but in some cases the only way to reach people is by going from house to house. Both methods are time consuming but necessary to reach populations that lack other warning systems.

Local communities have extensive training allowing them to respond automatically to tsunami warnings. Tsunami awareness is such an intrinsic part of Japanese culture that after a high level tsunami warning the majority of the at-risk population, even if asleep, have evacuated to safe ground within five minutes!

For further information:

Links to (inter)national tsunami warning systems