Tsunami Warning Systems have been progressively developed over the past six decades, with significant expansion and improvement in the last 20 years, in the aftermath of the 2024 Indian Ocean tsunami. In the NE Atlantic and Mediterranean region (NEAM), five Tsunami Service Providers (TSPs) (Portugal, France, Italy, Greece, Turkey) are operating on a permanent basis, following recommendations of the IOC/UNESCO within the ICG/NEAM (Intergovernmental Coordination Group). Frequent exercises are necessary to ensure a high level of operation and preparedness. Every 2-3 years, ICG/NEAM organizes regional exercises, called NEAMWave. The NEAMWave26 exercise was conducted in March 2026 to test the TSPs’ warning chains and procedures at multiple operational levels. Five scenarios were designed across the NEAM region. The scenario built for the NE Atlantic is based on the 1755 Lisbon earthquake, with an estimated moment magnitude of approximately 8.5. This event triggered a catastrophic tsunami and remains the largest natural disaster in Europe in the last 500 years, in terms of loss of lives and destruction. We present here a detailed analysis of this scenario and the lessons learned from the NEAMwave26 exercise in the NE Atlantic. Using numerical modeling, we show how tsunami waves propagated across the NE Atlantic, generating hazard and threat levels, both at regional and local scales. The tsunami warning messages issued by two operating TSPs (CENALT, France, and IPMA, Portugal) are presented to illustrate the sequence of the operational procedures in response to tsunami threat in the NE Atlantic. Moreover, the exercise outcomes are analyzed in light of feedback from subscribers and local authorities to draw key lessons learned from this exercise.

Tsunamis pose a low-frequency but high-impact hazard to coastal communities in the North-Eastern Atlantic and Mediterranean (NEAM) region. They are destructive, and their occurrence cannot be predicted. However, communities can take measures to decrease their impact. As concern grows for the NEAM region, local and international efforts are beginning to promote a complex legal and operational approach to hazard assessment, evacuation plans, and the establishment of effective Standard Operating Procedures (SOPs) for Early Warning Systems. This study reviews the evolution of tsunami preparedness in the North-Eastern Atlantic, the Mediterranean, and the adjacent seas, and recommends a shift from technically oriented warning systems to community resilience. Developments in this area are often delayed by inconsistent public awareness and the low priority given to coastal hazards in policy agendas. To address these vulnerabilities, the present paper underscores the need for continuous international cooperation, institutionalized education, and the deployment of innovative technologies.

The NASA-CNES altimetry mission SWOT (Surface Water and Ocean Topography) deployed in December 2022 embarks a Ka-band Radar Interferometer (KaRIn), providing a 120 km-wide swath sea level measurement. On 19 May 2023, SWOT was able to record a 2D signature of the tsunami generated by the Mw 7.7 earthquake southeast of the Loyalty Islands (southwest Pacific Ocean), about 1 h after the earthquake, on a straight SSW-NNE path. Comparison between numerical models and real measurements was performed to assess SWOT's ability to monitor tsunami waves. A uniform coseismic slip rupture model allows to satisfactorily fit the regional observations. Testing models against a dynamic representation of the tsunami wavefield (instead of static) show a good phase agreement, but simulated amplitudes are lower than the measurements. However, this SWOT unprecedented 2D observation critically inform on tsunami propagation and modelling, and offer a breakthrough perspective for better predictions.

During the last decades, trans-oceanic tsunamis have been captured by satellite altimeters on several occasions. The largest event ever measured by an altimeter was the 2004 Indian Ocean tsunami, captured by Jason-1, Topex/Poseidon, GFO and Envisat altimetry missions flying at that time The new altimetry mission SWOT (Surface Water and Ocean Topography) developed by NASA and CNES, the US and French Space agency respectively, was launched in December 2022. SWOT embarks a novel instrument, a Ka-band Radar INterferometer (KaRIN), providing a 120 km wide swath Sea Level. On 19 May 2023, SWOT was able to measure the tsunami generated by the Mw 7.7 earthquake which occurred southeast of the Loyalty Islands (southwest Pacific Ocean) at 02:57:03 (UTC). SWOT flew over the region about 1 hour after the earthquake and captured the tsunami signature in several locations. For the first time, a 2D mapview image of the height of tsunami wavetrain was measured by a satellite. The tsunami generation and propagation have been simulated using COMCOT model, using source parameters derived from seismic observations and empirical laws. Preliminary simulation results show that a simple fault plane with uniform coseismic slip allows to reproduce the regional coastal gauge and oceanic DART station records with a relatively good level of confidence, considering that the earthquake rupture was strongly not-double couple according to USGS. An array of virtual gauges was designed to cover the satellite pathway, allowing to extract the dynamic representation of the tsunami wavefield corresponding to the satellite propagation time (i.e., the sea surface deformation is observed over a period of time of several minutes, instead of being static at a given time). Comparison between the SWOT sea surface measurement and the simulation result is satisfactory, showing a good agreement between the location of the first wave peaks (propagating toward the southwest and the northeast, respectively), their amplitude and phase. The objective of this study is first to present this unprecedented observation, and to analyze the level of consistency with simulations.

Tsunamis are among the most devastating and infrequent natural phenomena, capable of causing immense loss of life and property in coastal regions. While predicting the occurrence of tsunamis remains challenging, communities can take proactive steps to mitigate their impact. Local, national, and intergovernmental initiatives aim to provide a legal framework for strengthening community preparedness through a comprehensive approach that includes measures ranging from tsunami hazard and exposure assessments, generating evacuation maps, installing corresponding signage, and promoting education and capacity building of local stakeholders and population. It also involves the establishment of Standard Operating Procedures (SOPs) to ensure a timely and effective end-to-end tsunami warning communication chain. This study presents an overview of the recent significant progress in tsunami preparedness across countries bordering the Mediterranean and North East Atlantic coasts.

On March 18, 2021, a magnitude Mw 6.0 earthquake occurred offshore the Algerian coasts near Bejaia, resulting in a tsunami with offshore amplitudes smaller than a few millimeters that crossed the western Mediterranean Sea. This study pursues three primary objectives: firstly, to assess the ability of tsunami simulations to replicate tide-gauge observations; secondly, to ascertain the relevance of seismic sources calculated within the context of tsunami early warning systems, against tsunami generation and observations; and thirdly, to evaluate the sensitivity of simulations to grid resolutions and earthquake parameters.Within the Mediterranean Sea, only a limited number of coastal tide gauges recorded the tsunami. Among these, select French tide gauge stations captured water waves with amplitudes smaller than a few centimeters and periods ranging from five to twenty minutes, often associated with harbor or bay resonances.Numerical simulations of the tsunami were conducted utilizing the operational code Taitoko employing six distinct source fault models. Notably, two of these models provided rapid source detection and characterization within the framework of tsunami warning systems at CENALT (Centre National d’Alerte aux Tsunamis, France). The integrated code Taitoko employs a system of multiple nested grids. For this event, it solved standard Boussinesq equations within the Mediterranean grid, while employing nonlinear shallow water equations in coastal and harbor grids, each with resolutions of 25 and 5 meters, respectively. Regardless of the fault model employed, the model satisfactorily reproduced the observed time series of water heights in both phase and amplitude at Nice and Monaco, while some discrepancies are found and discussed for most of the other locations.

The European-Mediterranean Seismological Centre (EMSC) provides rapid information on earthquakes and their effects, but does not operate seismic stations. It collects and merges parametric earthquake data from seismological agencies and networks around the world and collects earthquake observations from global earthquake eyewitnesses. Since its creation in 1975, it has developed strategies to complement earthquake monitoring activities of national agencies and coordinated its activities in Europe with its sister organisations ORFEUS and EFEHR as well as with global actors, while being part of the transformative EPOS initiative. The purpose of this article is to give a brief history of the EMSC and describe its activities, services and coordination mechanisms.

On March 18, 2021, a magnitude Mw 6.0 earthquake occurred offshore the Algerian coasts near Bejaia, resulting in a tsunami with offshore amplitudes smaller than a few millimeters that crossed the western Mediterranean Sea. This study pursues three primary objectives: firstly, to assess the ability of tsunami simulations to replicate tide-gauge observations; secondly, to ascertain the relevance of seismic sources calculated within the context of tsunami early warning systems, against tsunami generation and observations; and thirdly, to evaluate the sensitivity of simulations to grid resolutions and earthquake parameters.Within the Mediterranean Sea, only a limited number of coastal tide gauges recorded the tsunami. Among these, select French tide gauge stations captured water waves with amplitudes smaller than a few centimeters and periods ranging from five to twenty minutes, often associated with harbor or bay resonances.Numerical simulations of the tsunami were conducted utilizing the operational code Taitoko employing six distinct source fault models. Notably, two of these models provided rapid source detection and characterization within the framework of tsunami warning systems at CENALT (Centre National d’Alerte aux Tsunamis, France). The integrated code Taitoko employs a system of multiple nested grids. For this event, it solved standard Boussinesq equations within the Mediterranean grid, while employing nonlinear shallow water equations in coastal and harbor grids, each with resolutions of 25 and 5 meters, respectively. Regardless of the fault model employed, the model satisfactorily reproduced the observed time series of water heights in both phase and amplitude at Nice and Monaco, while some discrepancies are found and discussed for most of the other locations.

On 18 March 2021 an earthquake of magnitude Mw = 6.0 occurred offshore the Algerian coasts and generated a tsunami with offshore amplitudes smaller than a few millimetres crossing the western Mediterranean Sea. The objective of this study is threefold: first, to determine whether seismic sources calculated in the context of tsunami early warning are relevant; secondly, to determine whether tsunami simulations are able to reproduce tide-gauge observations and thirdly, to define the sensitivity of simulations to the grid resolutions and tsunami parameters. In the Mediterranean Sea, a very small number of available coastal tide gauges recorded the tsunami. Among them, a few French tide gauge stations recorded water waves with amplitudes smaller than a few centimetres and with periods ranging from 5 to 20 min associated to harbour or bay resonances. Numerical simulations of the tsunami are performed by the operational code Taitoko for seven different source fault models. Three of them allow for a rapid source detection and characterization in the framework of tsunami warning at CENALT (Centre National d'Alerte aux Tsunamis, France). The integrated code Taitoko uses a system of multiple nested grids. Standard Boussinesq equations are solved in the Mediterranean grid, whereas non-linear shallow water equations are solved in coastal and harbour grids with 25 and 5 m resolutions, respectively. Whatever the fault model, the observed time-series of water heights are reproduced satisfactorily both in phase and amplitude by the model at Nice and Monaco but poorly at Port Mahon (Minorca) and Toulon.

On 12 August 2021 a large Mw 8.1 earthquake, detected by global seismic networks, occurred on the South Sandwich subduction zone in the southern Atlantic Ocean. Approximately 1.5 hr later, a tsunami was clearly recorded on King Edward Point coastal tide gauge (South Georgia Island), approximately 800 km north-west of the earthquake location. Subsequently it was recorded on other coastal stations both in the Atlantic Ocean, and also in the Indian and Pacific Oceans. A careful and systematic analysis of coastal and deepwater sea-level records highlights three points: (a) the tsunami propagated across four oceans following major submarine features; (b) despite its very low amplitude, it reached as far as the Canary Islands in the Atlantic Ocean, Hawaii and the US West coast as far as Alaska and the Aleutian Islands in the Pacific Ocean; (c) it was recorded twice on New Zealand DART system NZC, with one record of the tsunami from the East and one from the West. This event is an opportunity to highlight the lack of knowledge about the South Sandwich subduction region in terms of its tsunamigenic potential and the associated tsunami hazard in the Pacific ocean. It should lead to an improvement of national tsunami warning procedures, by including this region as a tsunami source zone, for neighboring regions but also for distant countries like New Zealand or French Polynesia.

Meteotsunamis are long ocean waves generated by atmospheric disturbances. The Tonga volcano eruption on 15 January 2022 generated a Lamb pressure wave propagating all over the globe and generating a tsunami observed at most tide gauges in the world. A first atmospheric wave arrived 20 hours after the eruption on the French Mediterranean coasts and propagated southward. This abrupt atmospheric pressure change was recorded by hundreds of barometers of weather stations around Europe. A second one originating from Africa was observed four hours later with an attenuated amplitude. The first wave can be roughly defined by a sinusoid signal with a period close to one hour and an amplitude of 150 Pa. The associated tsunami was observed by the French stations of the HTM-NET network (https://htmnet.mio.osupytheas.fr/) [1]. Amplitudes range from a few cm to 15 cm and periods range from 20 min to 1 hour. Numerical simulation of the tsunami is performed by the operational code Taitoko developed at CEA [2]. The nested multigrid approach is used to simulate the water waves propagating in the bay of Toulon. The meteotsunami is generated by calculating analytically the atmospheric pressure gradient in the momentum equation. Comparisons of time series between numerical solutions and records are very satisfactory in regions defined by a high resolution topo-bathymetry. A second tsunami simulation is performed by introducing a second pressure wave propagating in the North direction and reaching the HTM-NET stations 4 hours after the first arrival. This second pressure wave results in additional and higher tsunami water waves in agreement with records. [1] Rey, V., Dufresne, C., Fuda, J. L., Mallarino, D., Missamou, T., Paugam, C., Rougier, G., Taupier-Letage, I., On the use of long term observation of water level and temperature along the shore for a better understanding of the dynamics: Example of Toulon area, France Ocean Dyn., 2020, https://doi.org/10.1007/s10236-020-01363-7. [2] Heinrich, P, Jamelot, A., Cauquis, A., Gailler A., 2021. Taitoko, an advanced code for tsunami propagation, developed at the French Tsunami Warning Centers. European Journal of Mechanics - B/Fluids 88(84) . DOI: 10.1016/j.euromechflu.2021.03.001.

In the framework of operational conditions, the real time coastal modeling in near field is challenging to obtain accurate and reliable tsunami warning products for flooding hazard. Maps of inundation and impacts for planning community response can be produced through coastal predictions with run-up computation by solving numerically high-resolution forecast models in real time, taking into account all local effects. However, these runs are too time consuming in near field and operational context. An alternative approach is based on early prediction tools of the coastal wave amplitude calculated from empirical laws or transfer functions derived from these laws. Such tools are suitable in near field context (almost ten times faster than the high-resolution runs), but all local effects are not well taken into account and the assessment of run-up is missing. The linear approximations of coastal tsunami heights are provided very quickly using the maximum wave heights from a computationally cheap regional forecast, with global and conservative estimates.Within the French Tsunami Warning Center (CENALT), a forecasting tool based on a transfer function method is being implemented. This fast prediction technique is based upon a recently extended version of the usual Green's Law (Giles et al., 2022[1]), which introduces local amplification parameters with the aim of capturing the neglected localized effects. The method includes an automated approach which optimizes for these local amplification parameters by minimizing a cost function.Local amplification parameters are calculated for the entire French Mediterranean coastline at 25 m resolution from a data set of 12 scenarios (high-resolution simulations). The forecasting results capabilities are analyzed, and shown for several coastal sites. The local tsunami wave heights modeled from the transfer function present a good agreement with the time-consuming high resolution models. The linear approximation is obtained within 1 min and provides globally estimates within a factor of two in amplitude. Although the resonance effects in harbors and bays are not reproduced and the horizontal inundation calculation needs to be studied further, this tool is well suited for an early first estimate of the coastal tsunami threat forecast. [1] Giles, D., Gailler, A., & Dias, F. (2022). Automated Approaches for Capturing Localized Tsunami Response—Application to the French Coastlines. Journal of Geophysical Research: Oceans, 127(6), e2022JC018467.

On the 12th of August 2021 at 18:32:54 and 18:35:20 (UTC) a doublet of reverse faulting earthquakes of magnitude Mw 7.5 and 8.1 were recorded by seismic observatories. These earthquakes were located on the South Sandwich Islands (UK) subduction zone, in the south Atlantic Ocean at 25.032°W/57.567°S and 25.327°W/58.451°S respectively (USGS locations). Initially, their temporal proximity (2’26”) made clear distinction of the two events impossible and a tsunami warning was issued by the PTWC after the first earthquake only. In fact, a tsunami was clearly recorded ~800 km north-westward of the epicentre on nearby King Edward Point coastal gauge (South Georgia Island, UK) ~1.5 hours after the shaking, showing a maximum amplitude of ~74 cm. While tsunami waves were recorded by neighbouring gauges located in the south Atlantic Ocean and the south-west Indian Ocean, numerical simulations of wave propagation show that this tsunami appears likely to have reached far-field regions not only in the Atlantic Ocean, but also in the Indian and Pacific Oceans using oceanic ridges like the Mid-Atlantic and Atlantic-Indian ridges as waveguides. Analysis of 33 records from gauges located within the maximum amplitude lobes of the simulated tsunami validates the modelling and the nearly worldwide spread of this tsunami. Further tsunami simulations using high-resolution nested grids to refine the bathymetry around the gauges (e.g. La Réunion Island, Cocos, Hillary Harbour) are used to constrain the source model via tsunami waveform inversion, comparing the calculated results and the real records. Consequently, we highlight that this tsunami reached many places including the Canary Islands, Cape Verde and the Azores in the northern Atlantic Ocean, and French Polynesia, New Zealand, Hawaii and as far as the Aleutian Islands in the Pacific Ocean, making this subduction zone a source for further consideration in tsunami hazard assessments of these distant regions, especially in the case of a more energetic rupture. Although the largest known event in the instrumental period is the 27 June 1929 MPAS 8.3 earthquake, geological knowledge of the region suggests that this ~1000 km long convergence zone between the South American and the South Sandwich plates with a convergence rate of 69-78 mm yr−1, is potentially able to produce a Mw 9.0 earthquake. This is supported by recent studies showing that the sediment thickness of 2-3 km at the trench and the ~150 km wide subduction interface shallow dipping (< 20° in the forearc part) are positive factors for generation of earthquakes Mw > 8.5. Results of simulation of Mw 9.0+ scenarios rupturing most of the subduction zone are discussed as well as the particular role of the oceanic ridges in the tsunami propagation. Our research aims to improve understanding of tsunami hazard posed by this subduction zone, especially for southern hemisphere coastlines.

The devastating Mw 7.1 Haiti earthquake in 2010 was accompanied by local tsunamis that caused fatalities and damage to coastal infrastructure. Some were triggered by slope failures of river deltas in the close vicinity of the epicenter, while others, 30 to 50 km to the north across the Bay of Gonâve, are well explained by the reverse component of coseismic ground motion that accompanied this mostly strike-slip event. However, observations of run-up heights up to 2 m along the southern coast of the island at distances up to 100 km from the epicenter, as well as tide gauge and DART buoy records at distances up to 600 km from the epicenter, have not yet received an explanation. Here we demonstrate that these observations require a secondary source, most likely a submarine landslide. We identify a landslide scar 30 km from the epicenter off the southern coast of Haiti at a depth of 3500 m, where ground acceleration would have been sufficient to trigger slope failure in soft sediments. This candidate source, 2 km3 in volume, matches observations remarkably well assuming that the sediment collapse obeys a viscous flow with an initial apparent viscosity of 2×105 Pa s. Although that particular source cannot be proven to have been activated in 2010, our results add to a line of evidence that earthquake-triggered submarine landslides can cause significant tsunamis in areas of strike-slip tectonic regime.

The May 2010 submarine volcanic crisis of the shallow South Sarigan Seamount (Marianas arc) ended on May 29 by a violent explosion that emitted a 12 km high atmospheric plume and created a crater 350 min diameter. The application of the multiphase localization method to the Pg, P, T phases of this explosion allows us to refine considerably (mainly based on the intense and impulsive T phases) the location of their source, that fits the position of the newly-formed South Sarigan crater. We highlight the numerous similarities of this final explosion with artificial underwater explosions (conventional or nuclear tests of known energy). Especially, the explosive nature of the source in the volcanic basement is confirmed by the similarity of the P phases with those of underground nuclear tests and the application of discriminating criteria Ms. - mb. The explosive nature of the source in the water is also confirmedby the application of the identification criteria for hydroacoustic sources and the T phases exceptionally impulsive and of short durations. These similarities allow us to provide a rough evaluation of the energy released by the South Sarigan final explosion using the methods commonly applied to man-generated explosions. We estimate a minimal released energy of 1 kt (4.2 x 10(12) J) for the seismic effects of the shock and ca 1 t of equivalent TNT (i.e. 4.2 x 10(9) J) for the hydroacoustic effects of the explosive source in the water. The processes leading to this final explosion are discussed on the basis of the sequence of the earlier seismic and eruptive events. Within the Comprehensive Nuclear-Test Ban Treaty framework, this explosion that affected concomitantly the solid, liquid and subaerial media is the first well documented one having generated intense waves: (P), hydroacoustic (T), acoustic (infrasounds) and tsunamis. (C) 2020 Elsevier B.V. All rights reserved.

Most tsunamis occur after large submarine earthquakes, particularly in the Pacific Ocean. However, following the 2004 tsunami in the Indian Ocean, tsunami hazard awareness was significantly raised at the global scale, and warning systems were developed in many other regions, where large tsunamis are rarer but can also produce large catastrophes. Here we first review the basic physics of a tsunami, from its triggering to its coastal impact, and we offer a review of the geophysical and sea-level data that can describe the various processes operating during a tsunami. Global Navigation Satellite System (GNSS) data have a key role in better describing the ground deformation following a tsunamigenic earthquake close to the coast. The GNSS observations complement seismological data to constrain the rupture model rapidly and robustly. Interferometric Synthetic Aperture Radar (SAR) also contributes to this field, as well as optical imagery, relevant to monitoring elevation changes following subaerial landslides. The observation of the sea-level variations, in the near field and during the propagation across the ocean, can also increasingly benefit from GNSS data (from GNSS buoys) and from robust satellite communication: pressure gauges anchored on the seafloor in the deep ocean contribute to warning systems only by data continuously transmitted through satellites. The sounding of ionospheric Total Electron Content (TEC) variations through GNSS, altimetry, or a ground-based airglow camera, is a promising way to record tsunami initiation and propagation indirectly. Finally, GNSS, optical and SAR imagery are essential to map and quantify the damage following tsunami flooding. Satellite data are expected to contribute more to operational systems in the future provided they are reliably available and analysed in real time.

In the evening on December 22, 2018, the Sunda Strait, Indonesia, suffered a destructive tsunami that no one had seen coming. It killed more than 400 people, injured and displaced thousands more. Post event satellite images indicate that the tsunami was probably caused by the collapse of a part of the southwestern flank of the Anak Krakatau volcano. Assuming a landslide volume of 150 million m 3 sliding into water as a granular flow under gravity forces, the simulated water waves are in general agreement with the tide gauges that recorded the tsunami.