SENAT
Report n° 117 (2007-2008) by M. Roland COURTEAU, Senator (for the parliament office for the evaluation of scientific and technological choices) - Appendix to the minutes of the 7 December 2007 session
Disponible au format Acrobat (21 Moctets)
c) The waiting game in the Northeast Atlantic and Mediterranean zones
The intergovernmental coordination group for the Northeastern Atlantic and Mediterranean zone has already met four times: in Rome in November 2005, in Nice in May 2006, in Bonn in February 2007 and in Lisbon in late November 2007. However, it would appear to be difficult to set up a tsunami warning system for this zone.
The seismic coverage of the Mediterranean zone countries is far from being homogeneous, with regard to both the number of seismic stations and the type of seismometer installed. In addition, many countries, particularly the North African states, refuse to provide access to their data. However, the rapid detection of an earthquake and the reliable localization of its epicentre, depth and magnitude require a dense network of seismometers, whose data is available to everyone. Insofar as those sources liable to provoke a Mediterranean-wide tsunami are located along the faults off the coast of North Africa, the unaccommodating attitude of these countries constitutes a major obstacle.
Furthermore, very few tide gauge stations transmit their data in real time, which means this information cannot be used to generate tsunami warnings or verify whether a tsunami has indeed been induced. As regards the most modern tide gauge stations (as well as many seismic stations), data transmission is carried out not by satellite but by Internet, even though this means of communication may be disrupted by an earthquake.
The working group on instruments for measuring sea level has selected some thirty particularly strategic tide gauges and urged those countries responsible for managing and processing their data to render them operational for the detection of tsunamis 39 ( * ) before the end of 2007. However, its success depends on the goodwill of these countries, since no specific funding has been set aside for this action. Therefore, this programme risks to be delayed, considering the difficulty encountered by the organizations responsible for the tide gauges in obtaining funds for their improvement. For example, SHOM ("Marine Hydrographic and Oceanographic Service"), responsible for improving the performance of tide gauges located on the French coasts, has already announced that, due to a lack of funding, only data from Le Conquet tide gauge will be transmitted in real time in 2007.
List of tide gauges judged to have priority for the setting up of a tsunami warning system in the Mediterranean
Source: IOC
In addition to an unwillingness to share seismic data, the setting up of an effective tsunami warning system meets with the refusal of numerous North African countries to transmit their tide gauge data.
Likewise, the lack of funds makes installing pressure sensors at sea difficult.
In addition to the question of tsunami detection, it seems that no country has begun to elaborate a warning plan laying out the measures to be taken by all the various authorities responsible for civil protection. No inundation zone has been delineated, no evacuation plan is operational. The warning methods have not been defined (sirens, radio messages, etc.) and no public awareness and education programme has been carried out.
Your rapporteur has observed that the European Union, represented by the European Commission, was not involved in setting up the tsunami warning system for the Mediterranean/Northeast Atlantic zone. This absence is surprising for several reasons.
Firstly, this project is by its very nature European: all the European countries are concerned, some because they border the Mediterranean, the others because a significant portion of their population spends its holidays on the coasts of the Mediterranean countries.
In addition, this project necessitates the installation of infrastructures (seismic stations, tide gauges, tsunamimeters) that are useful to all the countries, but which still rely on national funding. Therefore, the European Union should take responsibility for a portion of this instrumentation via European programmes; this would certainly accelerate the setting up of a warning system.
Finally, this project will only become operational if the North African countries decide to cooperate. The European Union can encourage them to do so within the framework of its European-Mediterranean policy.
In the opinion of your rapporteur, the elaboration of a clear tsunami warning strategy for the Mediterranean/Northeast Atlantic zone is confused by two additional factors: the diversity of tsunami sources and the desire to create a multi-risk system.
The warning systems currently being set up in the Indian Ocean, the Caribbean and the Mediterranean/Northeast Atlantic are designed to detect regional tsunamis and teletsunamis; in other words, tsunamis which are mainly provoked by earthquakes and whose source is sufficiently distant to provide an interval of between 20 minutes and several hours before their arrival on the coasts. For those coasts touched sooner (i.e., located nearer the source), the planned warning system is not yet operational, because the delays are too short and no country has decided to automate its warnings using sirens.
However, research on the sources of Mediterranean-zone tsunamis shows that the danger is not simply seismic in origin, but also linked to landslides and volcanic eruptions. There is therefore a significant risk of local tsunamis, even though this risk cannot be suitably managed by the proposed system. Therefore, certain countries are questioning the validity of this system, because it does not address local tsunamis.
In the opinion of your rapporteur, this attitude is hardly justified: considering the difficulties already encountered in setting up a regional tsunami warning system, it would be unrealistic to want to make the system operational at this stage for local tsunamis. Indeed, local tsunamis demand a very dense network of instruments and a permanent monitoring of zones of "gravitational instability" and volcanoes, both of which can only be ensured by the concerned countries. It should be pointed out that in the Pacific system, PTWC also functions as the local warning centre for Hawaii. Therefore, those countries of the Mediterranean/Northeast Atlantic zone particularly vulnerable to local tsunamis will eventually be induced to develop national or even local warning systems. For instance, Italy has installed a permanent monitoring system for Stromboli, following the tsunami of 30 December 2002.
Furthermore, this geographical zone (Mediterranean/Northeast Atlantic) is not homogeneous in its exposure to tsunamis. Northern Europe is less concerned by tsunamis than it is by storm surges. Therefore, these countries have accepted to participate in setting up a tsunami warning system only if the said system takes into account all risks of oceanic origin.
The supporters of this multi-risk approach believe that it should be easier to finance instruments for measuring sea level, because they can be used for the detection of several types of risk. However, extending the warning system to include several risks could also delay its implementation. Indeed, the necessary scientific knowledge is not the same: tsunami detection relies on a seismological network, while tempests fall within the competence of the meteorological services. Likewise, the prevention plans are independent, insofar as the necessary reaction times vary greatly. Even though establishing a system to manage a single risk proves to be a rather laborious process, requiring many meetings before any consensus can be formed, the decision-making process risks to be slowed down even further if other hazards must also be taken into account.
***
Since the Sumatra tsunami, the international community has realized that the tsunami risk is not limited to the Pacific, but rather concerns all of the world's oceans and seas. Therefore, each basin has set about setting up a tsunami warning system.
The results have been unequal: the countries of the Indian Ocean, still very much affected by the disaster of 26 December 2004 and the three following tsunamis 40 ( * ) , remain strongly motivated. However, in the Caribbean and Mediterranean/Northeast Atlantic zones, with the populations having gotten over the initial shock provoked by Sumatra, most of these countries (including France) now seem reticent to invest in a permanent warning system, considering the rarity of the hazard.
* 39 Initially, these tide gauges must be capable of sending a signal every minute when they are located more than 1 hour (or 100 km) from a tsunami-generating source, with eventually messages being sent every 15 seconds.
* 40 The three tsunamis generated after that of 26 December 2004 are the tsunamis of 28 March 2005, 17 July 2006 and 12 September 2007, each of which claimed victims. This has put into perspective the "exceptional" character of the Sumatra tsunami, which certain persons have used to justify the absence of a warning system in this region.