North-Eastern Atlantic, Mediterranean and connected seas

Tsunami Information Centre

General Information

 

TSUNAMI MESSAGES

TYPES OF MESSAGES

Tsunami messages refer to all messages issued by RTWCs in the NEAM region that are destined to the National TWFPs and/or NTWCs for further processing by emergency management agents (directly or second hand). Its content must convey the basic information required by these authorities. If there is a threat of any sort to the coastal areas, the messages related to this threat are called tsunami alert messages.

Ideally, the name of the tsunami alert message should already provide 3 of the main instances of information required by emergency management agencies (following CAP notation): urgency, severity, and certainty. The forth required information, the affected area, would appear immediately in the text of the message as the list of countries concerned by that particular message type. In this way, the very first few lines of a tsunami message would convey already the basic tsunami information to the recipient. The details of the threat evaluation would appear later in the message.

For each information instance, urgency, severity, and certainty, we suggest 2 levels of threat:

  Level I (high) Level II (low)
Urgency Tsunami to arrive in less than 21 hours Tsunami to arrive in more than 21 hours
Severity Tsunami wave height greater than 0.5m and/or tsunami run-up greater than 1m Tsunami wave height less than 0.5m and/or tsunami run-up less than 1m
Certainty Tsunami confirmed by sea-level measurements Tsunami not yet confirmed by sea-level measurements, information based on seismic parameters only
1Number to be agreed upon the ICG

 

And for each level we suggest the use of the following keywords to classify them :

Level definition for the 3 parameters
  Level I (high) Level II (low)
Urgency Immediate More than 2 hours
Severity1 Watch Advisory
Certainty Confirmed Not yet confirmed
1Number to be agreed upon the ICG

 

Using all combinations possible we could have 8 message types that are formed by combinations of the words selected for each level in the table above. This is a very high number of messages that could be confusing for the users and so we propose the following simplifications.

Firstly, in the NEAM region the reception of a tsunami alert message requires an immediate action to be taken by the agents and so the urgency field can be omitted.

As regards certainty, the information will be provided in the content of the message and proper training of the agents involved will help the emergency managers to grasp fast this content. In fact, the first message related to a tsunami threat will be always based exclusively on seismic information. This information, by itself, is not sufficient to decide if a tsunami was indeed generated and so its certainty is low. The Tsunami Response Plan in each country should define the actions to be taken in this case. When sea-level data is gathered and processed, following messages should confirm, update the threat or cancel it with a very high degree of certainty. And so, in a series of messages related to the same tsunami threat, the sequential order of messages do represent an implicit increase in certainty and this fact should be understood by the message recipients.

These simplifying options leave us with only two types of tsunami alert messages that convey only the severity information in its name:

Message type Tsunami Wave Effects on the coast
Tsunami Watch Tsunami wave height greater than 0.5m and/or tsunami run-up less than 1m Coastal inundation
Tsunami Advisory Tsunami wave height less than 0.5m and/or tsunami run-up less than 1m Currents, Bore, recession, damage in harbours, small inundation on beaches

 

In addition to the tsunami alert messages, we have to consider two additional types of messages, tsunami information and tsunami communication test.

The Tsunami Information is a message issued to advise the NEAM recipients of the occurrence of a major earthquake in the area but with an evaluation that there is no tsunami threat. The thresholds for the issuing of this type of messages are defined in the Decision Matrixes for the Mediterranean and for the NE Atlantic, as agreed by the ICG/NEAMTWS (see below).

For the National Tsunami Warning Centres (NTWCs) it is recommended that a National Tsunami Information message could be sent in the case of an earthquake felt at or close to the coast, of any magnitude. The tsunami information message will then be used to prevent unnecessary evacuations most frequently.

The Tsunami Communication Test is a message issued by the RTWCs at unannounced times to test the operation of the tsunami warning systems.

 

STRUCTURE OF MESSAGES, AFFECTED AREA AND SEQUENCE

In the NEAM region, due to its basin structure, there is no tsunami that can affect all countries with the same threat level. However, it could be confusing to send different messages to different countries referring to the same tsunami event. We propose that all National TWFP in the NEAM region will receive the same tsunami message. This means that the same message will contain in the same body more than one type of messages: tsunami watch, tsunami advisory, and tsunami information. We propose that the header part of the tsunami message should contain the sequence of pairs of fields, message type and affected area, by a decreasing order of threat. The type of such a composed message will be the one that corresponds to the highest level of tsunami threat. This means that some coastal area in the NEAM region is subject to that type of tsunami threat. Thus, a Tsunami Watch message will also contain a Tsunami Advisory and a Tsunami Information types of messages, while a Tsunami Advisory will contain also a Tsunami Information type of message. The area affected by a certain tsunami threat is defined in the Decision Matrixes agreed by the ICG/NEAMTWS, according to 3 spatial ranges of tsunamis:

 

Tsunami range Mediterranean NE Atlantic
Local < 100km < 100km
Regional 100km to 400km 100km to 1000km
Basin > 400km > 1000km

  

The tsunami message type related to one given country is defined by the worst case that can be found on any coastal area of that country, set up according to the Decision Matrix.

Decision Matrix for the NE Atlantic

        Tsunami Message Type
Depth Location Mw Tsunami Potential Local Regional Basin
< 100 km

Under or very near the sea (D < 30km) 5.5 to 7.0 Small potential for a destructive local tsunami Advisory Information Information
7.0 to 7.5 Potential for a regional tsunami Watch Advisory Information
7.5 to 7.9 Potential for a destructive regional tsunami   Watch Watch Advisory
> 7.9 Potential for a destructive basin-wide tsunami  Watch Watch Watch
Inland (D > 30km) ≥ 5.5 No tsunami potential Information Information Information
≥ 100km All locations ≥ 5.5 No tsunami potential Information Information Information
D represents the shortest distance between the epicentre and the coast line

 

Decision Matrix for the Mediterranean

        Tsunami Message Type
Depth Location Mw Tsunami Potential Local Regional Basin
< 100 km

Under or very near the sea (D < 30km) 5.5 to 6.0 Small potential for a destructive local tsunami Advisory Information Information
6.0 to 6.5 Potential for a destructive local tsunami Watch Advisory Information
6.5 to 7.0 Potential for a destructive regional tsunami   Watch Watch Advisory
> 7.0 Potential for a destructive basin-wide tsunami  Watch Watch Watch
Inland (D > 30km) ≥ 5.5 No tsunami potential Information Information Information
≥ 100km All locations ≥ 5.5 No tsunami potential Information Information Information
D represents the shortest distance between the epicentre and the coast line

 

The Tsunami Information and Tsunami Communication Test messages will be singles. They will not be followed by any further message related to the same tsunami event. This will no be the case for Tsunami Alert Messages, Advisories and Watches.

When there is a tsunami threat that deserves the issuing of a Tsunami Alert Message, the threat must be followed by the NEAM RTWC and a sequence of messages is expected until the alert is ended or is cancelled after the observation of sea-level measurements.

 

The first tsunami alert message in a sequence related to a tsunami threat is based exclusively on seismic information. This information, by itself, is not sufficient to decide if a tsunami was indeed generated and so its certainty is low. The subsequent messages will already contain an evaluation of the tsunami threat with sea-level measurements. These supplement second messages may confirm the previous alert, change the level of alert or cancel it. If there is a significant change in the revised earthquake parameters, like its magnitude, location or focal depth, that change the estimated tsunami threat, then a supplement tsunami alert message may be sent by the RTWC conveying this information.

A Tsunami Alert message is ended when the RTWC estimates that the tsunami threat is over and no more tsunami waves are expected and its effects subdued.

Two situations are considered : 

  • a tsunami has been observed : the message is end of watch or end of advisory
  • no tsunami was generated : the message is tsunami watch cancelation or tsunami advisory cancelation

This message cannot be interpreted as an "all-clear" message. The issuing os "all-clear" messages is a national responsibility of the emergency managers and should take into account the local safety conditions.

Any Tsunami Alert Sequence is the composed of one initial message; zero, one or more supplement messages and is always finished by an end of alert or alert cancellation message. The sequencing of tsunami messages is summarized in the table below.

 

Sequencing in Tsunami Messages
Message Type #1 #2 ... #N-1 #N
Tsunami Watch Initial supplement (0, 1 or more) end of watch
or watch cancellation

Tsunami Advisory
Initial

supplement (0, 1 or more)

end of advisory
or advisory cancellation
Tsunami Information Single    
Tsunami Communication Test Single    

Source: Interim Operational Users Guide for the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and Connected Seas, v.1.1g