SAFE - Tsunami early warning system using available seafloor fiber cables with Chirped-pulse DAS

Traditional tsunami early warning systems (TEWS) are typically expensive, have limited real-time availability, require continuous maintenance, and involve long deployment times. The SAFE project aims to overcome these limitations by developing a new tsunami warning technology based on Distributed Acoustic Sensing (DAS), leveraging existing seafloor fiber optic cables. This approach offers continuous 24/7 monitoring, near-zero maintenance, faster response times, and ease of installation. The project includes contributions ranging from the development of a novel Chirped-pulse DAS interrogator (HDAS) with improved low-frequency performance to a novel post-processing software to obtain tide height from the measured seafloor strain and automatic detection and confirmation of a tsunami wave. All this has been implemented in a friendly user interface and is undergoing final evaluation by the tsunami warning authority in the NE Atlantic (the Instituto Português do Mar e da Atmosfera, IPMA). The validation is currently ongoing using the ALME subsea cable, which connects Almería and Melilla across the Alboran Sea. The interrogator has demonstrated the ability to detect swell waves with a maximum error of 20 cm in the deep sea and a post-processing response time of less than 90 seconds. It is expected that slower tsunami waves will yield more precise estimations of wave height.Importantly, the technology could also successfully detect the 5.3 Mw earthquake near Cabo de Gata, Spain, on July 14, 2025, at a distance of only 40 km from the epicenter without major saturation. The extremely large dynamic range of the interrogator (approximately 10 times larger than a usual phase system) enables the system to monitor large-magnitude earthquakes without signal clipping. The SAFE system is capable of delivering critical seismic and hydrodynamic data within 5 minutes of an event, supporting early tsunami detection and rapid response.