Page Text: 500-600 miles per hour (in deep water) 20-30 miles per hour (near shore)
5-60 miles per hour
4. Tsunami Detection and Forecasting
4.1 What are the responsibilities of the Tsunami Warning Centers?
The NWS operates two Tsunami Warning Centers, which are staffed 24 hours a day, 7 days a week. The main mission of the warning centers is to help protect life and property from tsunamis. To do this, they monitor observational networks, analyze earthquakes, evaluate water-level information, issue tsunami messages, conduct public outreach, and coordinate with the National Tsunami Hazard Mitigation Program and government, academic, and international organizations to continually improve their operations.
4.2 How are tsunamis detected?
The Tsunami Warning Centers depend on an observation system that includes seismic and water-level networks from around the world to help them determine when and where to issue tsunami messages. These networks are critical to the warning centers’ ability to provide timely and accurate messages:
Seismic Networks—When an earthquake occurs, seismic networks provide information about an earthquake’s location, depth, magnitude, and other source characteristics. The warning centers analyze this information to determine if the earthquake could have generated a tsunami and if a tsunami message is necessary.
Water-Level Networks—If an earthquake meets certain criteria, the warning centers turn to water-level information, looking for changes in water-level height that could indicate the existence and size of a tsunami. The primary sources of information about water-level change are a network of Deep-ocean Assessment and Reporting of Tsunami (DART) systems and an extensive array of coastal water-level stations .
4.3 What is a DART system?
DART (Deep-ocean Assessment and Reporting of Tsunami) systems were developed by NOAA for the early detection, measurement, and real-time reporting of tsunamis in the open ocean. The NWS’s National Data Buoy Center operates and maintains the U.S. network of DART systems, which is part of a larger international network. The U.S. network is composed of 39 systems (as of 2016) strategically located throughout the Pacific and Atlantic Oceans, the Gulf of Mexico, and the Caribbean Sea.
Each system consists of a bottom pressure recorder (BPR) anchored on the ocean floor and a separately moored companion surface buoy. When a tsunami passes over a BPR, the instrument detects and records the changes in the overlying water pressure. An acoustic link transmits information from the BPR to the surface buoy, which then relays it via satellite to the warning centers where the information is incorporated into tsunami forecast models.
See how a DART system works (video).
4.4 What is a coastal water-level station?
Coastal water-level stations collect important information about the height of the ocean at specific coastal locations. Their primary purpose is to monitor tides for navigation purposes, thus they are located on the coast (in contrast to the DART systems, which are in deep water), generally on piers in harbors. Information from these stations is relayed via satellite to the warning centers where it is used to confirm tsunami arrival time and height and is incorporated into tsunami forecast models. Coastal water-level stations are owned and operated by a number of national and international organizations. In the United States, most of the tsunami-capable coastal water-level stations (i.e., data is available in one-minute intervals) are operated and maintained by NOAA’s Center for Operational Oceanographic Products and Services as part of the National Water Level Observation Network.
4.5 How are tsunamis forecast?
In most cases, the first sign of a potential tsunami is an earthquake. Seismic waves travel about 100 times faster than tsunamis, so information about an earthquake is available before information about any tsunami it may have generated. Three key pieces of information about an earthquake help the Tsunami Warning Centers determine if it was capable of generating a tsunami: location, depth, and magnitude. The warning centers use this preliminary seismic information to decide if they should issue a tsunami message and at what alert level(s).
Once a message is issued, the warning centers conduct additional seismic analysis and run tsunami forecast models using information from the seismic and water-level networks as it becomes available. These numerical models use the real-time information and pre-established scenarios to simulate tsunami movement across the ocean and estimate coastal impacts, including wave height and arrival times, the location and extent of coastal flooding, and event duration. The resulting forecasts, combined with historic tsunami information and additional seismic analysis, help the warning centers decide if they should issue an updated or cancellation message.
It is more difficult to forecast nonseismic tsunamis (like landslide and volcanic tsunamis and meteotsunamis), which can arrive with little to no warning. Even if a nonseismic tsunami is detected by a DART system or coastal water-level station, there may not be time to develop a detailed forecast. In the case of meteotsunamis, NWS Weather Forecast Offices, with decision support from the warning centers, can notify the public of the potential coastal threat given the presence of or potential for certain weather conditions along with observed water-level measurements.
5. Tsunami Messages
5.1 What are tsunami messages?
Tsunami messages are issued by the Tsunami Warning Centers to notify emergency managers and other local officials, the public, and other partners about the potential for a tsunami following a possible tsunami-generating event. For the United States, Canada, and the British Virgin Islands, these messages include alerts. There are four levels of tsunami alerts: warning, advisory, watch, and information statement.
Initial tsunami messages include alert level(s), preliminary information about the earthquake, and an evaluation of the threat. If a tsunami is already suspected, the message may also include wave arrival times, recommended life safety actions, and potential impacts. Subsequent messages, both updates and cancellations, are based on additional seismic analysis and results from the tsunami forecast models and may feature more refined, detailed, and targeted information.
See examples of tsunami messages.
5.1.1 What is a tsunami warning?
A tsunami warning is issued when a tsunami with the potential to generate widespread inundation is imminent, expected, or occurring. Warnings alert the public that dangerous coastal flooding accompanied by powerful currents is possible and may continue for several hours after initial arrival. Warnings alert emergency management officials to take action for the entire tsunami hazard zone. Appropriate actions to be taken by local officials may include the evacuation of low-lying coastal areas and the repositioning of ships to deep waters when there is time to safely do so. Warnings may be updated, adjusted geographically, downgraded, or canceled based on updated information and analysis.
5.1.2 What is a tsunami advisory?
A tsunami advisory is issued when a tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring. The threat may continue for several hours after initial arrival, but significant inundation is not expected for areas under an advisory. Appropriate actions to be taken by local officials may include closing beaches, evacuating harbors and marinas, and the repositioning of ships to deep waters when there is time to safely do so. Advisories may be updated, adjusted geographically, upgraded to a warning, or canceled based on updated information and analysis.
5.1.3 What is a tsunami watch?
A tsunami watch is issued when a tsunami may later impact the watch area. The watch may be upgraded to a warning or advisory or canceled based on updated information and analysis. Emergency management officials and the public should prepare to take action.
5.1.4 What is a tsunami information statement?
A tsunami information statement is issued when an earthquake or tsunami has occurred of interest to the message recipients. In most cases, information statements are issued to indicate there is no threat of a destructive basin-wide tsunami and to prevent unnecessary evacuations. Information statements for distant events requiring evaluation may be upgraded to a warning, advisory, or watch based on updated information and analysis.
5.2 What is a tsunami threat message?
A tsunami threat message is a tsunami message for international partners in the Pacific and Caribbean. The United States does not issue alerts for these partners. The primary purpose of these messages is to help national authorities understand the threat to their coasts so they can determine which alerts to issue for their coastlines, if any. A threat message describes tsunami threats according to the potential hazard and impact to people, structures, and ecosystems on land or in nearshore marine environments. National authorities will determine the appropriate level of alert for each country and may issue additional or more refined information and instructions. A threat message may be updated based on new information, data, and analysis. An information statement may be issued following an earthquake or tsunami of interest to the message recipients if there is little to no threat, but may be upgraded to a tsunami threat message if warranted.
U.S. states and territories in the Pacific and Caribbean (American Samoa, Guam, Hawaii, Northern Mariana Islands, Puerto Rico, U.S. Virgin Islands) should refer *ONLY to the Pacific Tsunami Warning Center messages for their regions. International tsunami threat messages from the Pacific Tsunami Warning Center may mention U.S. states and territories, but they do not reflect the additional modeling and analysis conducted to fine tune forecasts and set alert levels for the United States and should not to be relied on by U.S. states and territories
See examples of tsunami messages.
5.3 Who issues tsunami messages?
The Tsunami Warning Centers prepare and issue tsunami messages for their respective designated service areas. Primary recipients of these messages include NWS Weather Forecast Offices, state emergency operations centers, the U.S. Coast Guard, the U.S. military, and designated international authorities. Each of these recipients is responsible for forwarding the message to its own constituents.
5.4 Who cancels tsunami messages?
The Tsunami Warning Centers issue a cancellation after they determine that a destructive tsunami will not affect an area under a warning, advisory, or watch or that a tsunami has diminished to a level where additional damage is not expected. However, the cancellation of a message does not mean the area is safe. The final decision that an area is safe is up to local and state emergency management officials.
5.5 What are the designated service areas of the Tsunami Warning Centers?
The National Tsunami Warning Center in Palmer, Alaska, serves the continental United States, Alaska and Canada.
The Pacific Tsunami Warning Center in Honolulu, Hawaii, directly serves the Hawaiian Islands, the U.S. Pacific and Caribbean territories, and the British Virgin Islands and is the primary international forecast center for the warning systems of the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization in the Pacific and the Caribbean and Adjacent Regions.
5.6 How do the Tsunami Warning Centers decide what alert levels to include in their messages?
The Tsunami Warning Centers base their initial tsunami messages on the preliminary earthquake information (location, depth, and magnitude) received from seismic networks since that is all the information available within the first few minutes after an earthquake. They use preset criteria ( Atlantic , Pacific ) to decide when to issue a tsunami message and what alert(s) to include. Subsequent messages and alerts are based on impact estimation resulting from additional seismic analysis, water-level measurements, tsunami forecast model results, and historical tsunami information.
Tsunami warnings are typically issued following coastal earthquakes magnitude 6.5 or greater for U.S. and Canadian Atlantic and Gulf coasts, and magnitude 7.1 or greater for all coasts along the Pacific Ocean and Caribbean Sea. Tsunami height also affects alert selection. In general, the warning centers issue a tsunami warning if the forecast or observed tsunami height exceeds 1.0 meter (3.3 feet) or the impact is unknown, and a tsunami advisory if the forecast height is between 0.3 and 1.0 meter (0.98 and 3.3 feet) or the observed height is between 0.5 and 1.0 meter (1.6 and 3.3 feet).
5.7 How quickly are tsunami messages issued?
The time it takes for a Tsunami Warning Center to issue a tsunami message depends on the seismic network density and distribution near the earthquake’s point of origin. In regions of high seismic network density, the warning centers can issue messages within five minutes. In areas of lower seismic network density, response time increases to 10-15 minutes.
5.8 How can I receive tsunami messages?
In the United States, tsunami messages are broadcast through local radio and television, marine radio, wireless emergency alerts , NOAA Weather Radio , NOAA websites (like Tsunami.gov ), and social media accounts (Facebook and Twitter). They may also come through outdoor sirens, local officials, emails and text message alerts from state and local opt-in systems, and telephone notifications. In some cases, like wireless emergency alerts that only broadcast the first tsunami warning, broadcast of a message may depend on the level of alert and/or local circumstances. There may not always be enough time for an official warning, so it is important to understand natural warnings.
6. Tsunami Safety
6.1 Why are tsunamis dangerous?
A tsunami is one the most powerful and destructive natural forces. It can produce unusually strong currents, rapidly flood land, and devastate coastal communities. Low-lying areas such as beaches, bays, lagoons, harbors, river mouths, and areas along rivers and streams leading to the ocean are the most vulnerable.
Most tsunami damage and destruction is caused by flooding, wave impacts, strong currents, erosion, and debris. The water can be just as dangerous as it returns to the sea, taking debris and people with it. In addition to loss of life and mass injuries, other potential impacts include damage to and destruction of homes and businesses, cultural and natural resources, infrastructure, and critical facilities. Flooding and dangerous currents can last for days. Even small tsunamis can pose a threat. Strong currents can injure and drown swimmers and damage and destroy boats in harbors.
Local tsunamis are particularly dangerous. They can strike a coast within minutes of generation with little or no warning.
6.2 How can I prepare for a tsunami?
Although tsunamis cannot be prevented, there are things you can do before a tsunami that could save your life and the lives of your family and friends. Importantly, find out if your home, school, workplace, or other places you visit often are in a tsunami hazard zone ( U.S. tsunami maps ).
If you live or spend time in a tsunami hazard zone:
Educate yourself about tsunami warnings (official and natural) and ensure you have multiple ways to receive official warnings. In the United States, get a NOAA Weather Radio , sign up for text message alerts from your local government, and verify that your mobile devices receive wireless emergency alerts .
Make an emergency plan that includes plans for family communication and evacuation.
Map out routes from home, work, and other places you visit often to safe places on high ground or inland (away from the water) and outside the tsunami hazard zone. Your community may already have identified evacuation routes and assembly areas (if they have not, identify a safe place at least 100 feet above sea level or 1 mile inland). Plan to evacuate on foot if you can; roads may be impassable due to damage, closures, or traffic jams.
Practice walking your routes, even in darkness and bad weather. This will ease evacuation during an emergency.
Put together a portable disaster supplies kit with items you and your family (including pets) may need in an emergency. Prepare kits for work and cars, too.
Be a role model. Share your knowledge and plans with others.
If you have children in school in a tsunami hazard zone, find out the school’s plans for evacuating and keeping children safe. If you are visiting the coast, find out about local tsunami safety. Your hotel or campground should have this information.
Visit the NWS Tsunami Safety and International Tsunami Information Center websites to learn more.
6.3 How will I know if a tsunami is coming?
There are two ways that you may be warned that a tsunami is coming: an official tsunami warning and a natural tsunami warning. Both are equally important. You may not get both.
In the United States, an official tsunami warning will be broadcast through local radio and television, marine radio, wireless emergency alerts , NOAA Weather Radio , and NOAA websites (like Tsunami.gov ) and social media accounts (Facebook and Twitter). It may also come through outdoor sirens, local officials, emails and text message alerts from state and local opt-in systems, and telephone notifications.
There may not always be time to wait for an official tsunami warning. A natural tsunami warning may be your first, best, or only warning that a tsunami is on its way. Natural tsunami warnings include strong or long earthquakes, a loud roar (like a train or an airplane) from the ocean, and unusual ocean behavior. The ocean could look like a fast- rising flood or a wall of water (bore). Or, it could recede suddenly, showing the ocean floor, reefs, and fish like a very low, low tide. If you experience any of these warnings, even just one, a tsunami could be coming.
6.4 How should I respond to a tsunami warning?
How you should respond to a tsunami warning depends on where you are and the type of warning you receive (i.e., official or natural). Be prepared to respond immediately to whatever you hear or see first.
If you are in a tsunami hazard zone and receive an official tsunami warning:
Stay out of the water and away from beaches and waterways.
Get more information from radio, television, or your mobile device (text or data) and continue to stay informed throughout the event.
If officials ask you to evacuate, implement your emergency plan and move quickly to your safe place. If you do not have a safe place or cannot reach it, follow evacuation signs to safety or go as high or as far inland (away from the water) as possible (at least 100 feet above sea level or a mile inland).
If you are in a tsunami hazard zone and receive a natural tsunami warning, a tsunami could arrive within minutes:
In case of an earthquake, protect yourself. Drop, cover, and hold on. Be prepared for aftershocks. Each time the earth shakes, drop, cover, and hold on.
Take action. Do not wait for an official warning or instructions from officials.
As soon as you can move safely, implement your emergency plan and move quickly to your safe place. If you do not have a safe place or cannot reach it, follow evacuation signs to safety or go as high or as far inland (away from the water) as possible (at least 100 feet above sea level or a mile inland).
If there is earthquake damage, avoid fallen power lines and stay away from weakened structures.
When you are in a safe place, get more information from radio, television, or your mobile device (text or data).
If you are on the beach or near water and feel an earthquake of any size and length, move quickly to high ground or inland (away from the water) as soon as you can move safely. Get more information from radio, television, or your mobile device (text or data).
If you are outside of the tsunami hazard zone and receive a warning, stay where you are unless officials tell you otherwise.
For your safety and others, always follow instructions from local officials and stay out of the tsunami hazard zone until they tell you it is safe. In the United States, to find out if you are in a tsunami hazard zone, visit the Tsunami Maps web page .
Visit the NWS Tsunami Safety and International Tsunami Information Center websites to learn more.
6.5 Who issues tsunami evacuation orders?
For all U.S. states and territories, evacuation requests/instructions are typically issued and coordinated by local emergency management officials. In the unique case of a tsunami warning issued for local Hawaii earthquakes, the Pacific Tsunami Warning Center decides whether evacuations are necessary. When they are, local and state emergency management officials coordinate them and are responsible for determining when it is safe for people to return to an evacuated area.
6.6 Will I be safe from a tsunami in a tall building?
Most buildings are not designed to withstand tsunami impacts. However, the upper stories of some strong (e.g., reinforced concrete) and tall buildings may be able to provide protection if no other options are available. If you are concerned that you will not be able to reach a safe place in time, ask your local emergency management office or hotel staff about vertical evacuation. Note, this type of evacuation is not recommended in all areas.
6.7 What do I do if I am in a boat in a harbor or at sea during a tsunami?
If you are on a boat and you get a tsunami warning, your response will depend largely on where you are.
In the United States, in general, it is recommended that:
If you are in a harbor and get a tsunami warning, you should leave your boat and move quickly to a safe place on land (high ground or inland, away from the water).
If you are at sea and get a tsunami warning, you should move to a safe depth* and stay away from harbors under warning until officials tell you the threat has passed.
* Safe depths vary by region , but the minimum safe depth is 30 fathoms (180 feet). Your harbor master, port captain, the U.S. Coast Guard, and local and state emergency management offices are the best sources for safe depth and other tsunami safety information and regulations for boaters in your area.
If you are a boat owner or captain, take extra steps to prepare for a tsunami:
Make sure you have a way to receive tsunami warnings when you are on the water. The U.S. Coast Guard will issue urgent marine information broadcasts on your marine VHF radio’s channel 16. Additional information will be available from NOAA Weather Radio .
Make a plan and put together a disaster supplies kit to keep on board your boat. Be aware that shore facilities may be damaged, so if you are at sea during a tsunami, you may not be able to return to the harbor you left. Be prepared to remain at sea for a day or more.
If you have a question regarding tsunamis we would like to hear from you .
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