The report of the UNESCO-IOC Expert Meeting in Vanuatu on Tsunami Sources, Hazards, Risk and Uncertainties Associated with the Subduction Zones of the Region is now available

21 January 2025

The report of the hybrid UNESCO-IOC Expert Meeting on Expert Meeting on Tsunami Sources, Hazards, Risk and Uncertainties Associated with Vanuatu, San Cristobal and New Britain Subduction Zones is now available as IOC-WR-315 .

The Expert Meeting was organized in Port Vila, Vanuatu during 14-17 May 2024 in close coordination with the Vanuatu Meteorology and Geo-Hazard Department (VMGD), bringing together 23 experts and 7 observers from ten Member States of the Intergovernmental Coordination Group for the Pacific Tsunami Warning and Mitigation System (ICG/PTWS) (Australia, France, Fiji, Japan, Indonesia, New Zealand, Papua New Guinea, Solomon Islands, USA and Vanuatu). The purpose of this Expert Meeting was to quantify earthquake sources that can generate dangerous tsunamis and to directly support community hazard assessments and evacuation planning that are part of the implementation of the Tsunami Ready Recognition Programmein the Pacific Islands Countries and Territories (PICTs).

During the Expert Meeting, the overall tectonics of the Study Region were considered, including the arrangement and relative rates of the tectonic plates (including microplates) and likely segmentation of the subduction zones. Non-subduction regions were identified and discussed as well as possible non-seismic tsunami sources. The outcomes of the meeting as reflected in this report included an endorsement with some updates of the earthquake sources identified by the 2012 Global Earthquake Model (GEM) Faulted Earth study of subduction zones worldwide (Berryman et al., 2015). The major differences included updating the lower limits of the maximum credible earthquakes for various parts of the subduction systems with more recent earthquake data, and a re-evaluation of the upper limits of maximum credible earthquakes for the various identified subduction zone segments. Some non-subduction zone regions with the potential to produce tsunami generating earthquakes were identified and characterised using a similar approach to the GEM methodology.

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Non-earthquake sources of tsunamis were also considered. For example, a list of volcanic sources capable of causing tsunamis in the region was built from published work, but not characterised in detail. Similarly, an attempt was made to identify potential landslide sources. An important outcome of the meeting was a list of potential tsunami source scenarios with parameters that can be employed for tsunami modelling informing preparedness and evacuation planning by Member States.

The report highlighted a number of recommendations for further scientific work to improve the knowledge of tsunami threats in the region. These include the need for a full probabilistic treatment of all potential tsunami sources and impacts in the region, more geodetic observations to constrain relative plate rates and slip deficit accumulation, and more paleotsunami studies to assess past tsunami occurrences. There is also a need to improve the sustainability and the spatial coverage of the instrument networks in the region and to encourage full and open sharing of data and scientific results.

An earthquake with a magnitude of 7.3 on 17 December 2024 01:47 (UTC) offshore Port Vila, Vanuatu ( USGS ) resulted in a Tsunami Threat Message issued by the Pacific Tsunami Warning Center (PTWC), one of the Tsunami Service Providers (TSP) of the ICG/PTWS, 5 min after the event indicating the possibility of hazardous tsunami waves for coasts located within 300 km of the earthquake epicenter along the coasts of Vanuatu. Initial tsunami amplitude forecasts were issued by the PTWC directly to the Tsunami Warning Focal Points (TWFP) of the ICG/PTWS after 34 min of event origin time, indicating the possibility of tsunami waves reaching 0.3 to 1 meters above the tide level to Vanuatu and less than 0.3 meters above the tide level for the coasts of Fiji, Kermadec Islands, Kiribati, New Caledonia, Papua New Guinea, Solomon Islands, Tuvalu, and Wallis And Futuna. At 0221 UTC, 1h 34 min after the event, PTWC updated the tsunami forecast based on the sea-level recording of 0.25m in Vanuatu, stating that tsunami waves reaching 0.3 to 1 meters above the tide level are possible for some coasts of Vanuatu. At 03:14 UTC, PTWC issued its final message indicated that is no longer a tsunami threat from this earthquake. This event was another reminder on the tsunamigenic potential of the region and was a testimony on the timeliness of the hybrid Expert Meeting to better identify this potential.