Periodic Reporting for period 1 - SAFE (SAFE: Tsunami early warning System using Availableseafloor Fiber cablEs)
Berichtszeitraum: 2022-12-01 bis 2023-11-30
According to the World Health Organization, more than 700 million people live in low-lying coastal areas and Small Island Developing States exposed to extreme sea-level events including tsunamis. The cost of the most reliable currently-available tsunami warning systems (based on offshore sensors) is extremely high and essentially only affordable to rich countries like the US or Japan. As such, the vast majority of all this endangered population is not yet protected by this type of tsunami warning system. Luckily, the vast majority of these coastal areas have alreadyavailable fibre-optic cables installed (for communication purposes) which could additionally serve as a key component for tsunami early warning, at a marginal extra cost. The objective of this project is to fulfill the need of protecting these communities, which often have limited resources, by providing a tsunami early warning solution based on the already-available fibre optic infrastructure. The solution provided in this project will be simple to deploy and maintain (just connecting an interrogator in the dry end of the fiber-optic cable), low cost (it will be several orders of magnitude cheaper than current systems), reliable (tsunami alerts will be confirmed by the same device using indirect measurements of sea level) and timely (the response time is expected to be faster than current systems). The main market of this solution will be official meteorological and environmental institutions of different countries responsible for issuing early warnings.
The core objective of the project is the development of a tsunami early warning product (TWS) comprising a long range distributed acoustic sensor (DAS) and the artificial intelligence (AI) layer capable of launching reliable alarms upon the detection of potential tsunamigenic activity and tsunami waves. Along the first year of the project, substantial progress has been made in relation to the development of the long-range (and low noise) DAS interrogator, and the creation of the necessary databases to develop the AI layer in the second year. With respect to the DAS interrogator, the project has achieved a DAS architecture that improves the strain noise performance of the previous high-fidelity DAS available in the market by at least a factor of 3, while also extending the range well beyond 80 km. In addition to this, the potential market of this solution has been better understood, and interesting demonstrations have been done to potential end-users. These include not only tsunami warning agencies but also (and probably more notably) cable owners interested in protecting their cables from threats such as anchors or trawlers.
The project has contributed to go beyond the scientific state of the art as evidenced in the following results:
- The DAS technology developed in the project has been essential to achieve the first high-resolution spatially-resolved visualization of tidal-driven internal waves in the ocean. These results prove that changes in the water column can be monitored with DAS, and particularly with our low-noise high-fidelity DAS system.
- We fhave done the first complete quantification of the potential contribution of all conceivable mechanisms by which a tsunami may generate longitudinal strain on a seafloor cable, including seafloor compliance and Poisson’s effect of the cable induced by hydrostatic pressure, seafloor shear and temperature transients induced by deep fluid flow. We found that the seafloor compliance and Poisson’s effect are the dominant mechanisms over the most relevant conditions. We also verified that our theoretical estimate of the seafloor compliance signal agrees with results of a fully-coupled 3D simulation of earthquake, tsunami and seismo-acoustic waves. We also quantified potential sources of environmental noise, in particular low-frequency background temperature fluctuations. We finally compared the signal amplitudes to the expected noise floor of low-frequency DAS interrogators. Overall, the analysis shows that tsunami can be detected with good signal-to-noise ratio by low-frequency DAS instruments, within a few minutes of the earthquake onset, on seafloor cables located above or near the source area.
- We are developing the first methods to achieve earthquake localization by backprojection of DAS data, with accuracies comparable to those obtained using in-land stations. This will allow issuing early warnings sooner than current systems.
The future uptake of our solution for tsunami warning will depend on a number of factors, the key one being the acceptance among cable owners. Therefore, the project is currently putting a significant focus in collecting evidence suggesting that this solution would be of interest for preventing threats to submarine cables, such as anchors or trawlers.
- The DAS technology developed in the project has been essential to achieve the first high-resolution spatially-resolved visualization of tidal-driven internal waves in the ocean. These results prove that changes in the water column can be monitored with DAS, and particularly with our low-noise high-fidelity DAS system.
- We fhave done the first complete quantification of the potential contribution of all conceivable mechanisms by which a tsunami may generate longitudinal strain on a seafloor cable, including seafloor compliance and Poisson’s effect of the cable induced by hydrostatic pressure, seafloor shear and temperature transients induced by deep fluid flow. We found that the seafloor compliance and Poisson’s effect are the dominant mechanisms over the most relevant conditions. We also verified that our theoretical estimate of the seafloor compliance signal agrees with results of a fully-coupled 3D simulation of earthquake, tsunami and seismo-acoustic waves. We also quantified potential sources of environmental noise, in particular low-frequency background temperature fluctuations. We finally compared the signal amplitudes to the expected noise floor of low-frequency DAS interrogators. Overall, the analysis shows that tsunami can be detected with good signal-to-noise ratio by low-frequency DAS instruments, within a few minutes of the earthquake onset, on seafloor cables located above or near the source area.
- We are developing the first methods to achieve earthquake localization by backprojection of DAS data, with accuracies comparable to those obtained using in-land stations. This will allow issuing early warnings sooner than current systems.
The future uptake of our solution for tsunami warning will depend on a number of factors, the key one being the acceptance among cable owners. Therefore, the project is currently putting a significant focus in collecting evidence suggesting that this solution would be of interest for preventing threats to submarine cables, such as anchors or trawlers.