Submarine measurements using optical fiber for the detection of earthquakes and tsunamis and integration into the Gulf of Cádiz monitoring and early warning network

FibrE-Optic IntegRated Monitoring and Alert Network for Earthquakes and Tsunamis in the Gulf of Cadiz (FERMAT)

The FERMAT project aims to develop and apply Distributed Fiber-Optic Sensing (DFOS) technology for seismic and oceanographic monitoring, with a specific focus on Distributed Acoustic Sensing (DAS). This cutting-edge approach leverages existing submarine telecom fiber-optic cables to transform them into dense, real-time seismic sensor arrays, overcoming the limitations of traditional offshore monitoring systems. By using DAS, we can detect seismic and oceanographic events across vast underwater regions, significantly improving earthquake and tsunami early-warning capabilities.

One of the primary objectives of FERMAT is to integrate DAS technology into Spain’s Red Sísmica Nacional (IGN), enhancing the existing earthquake and tsunami monitoring infrastructure. The project will focus on the Gulf of Cádiz, a region with a history of high-magnitude earthquakes and devastating tsunamis, yet currently lacking sufficient offshore instrumentation. To address this, FERMAT will utilize four existing submarine telecom cables: two in the Gulf of Cádiz (Spain), one in southern mainland Portugal, and one in Madeira. These collaborations will allow us to incorporate DAS into the operational earthquake and tsunami warning system of IGN, strengthening real-time hazard detection in the region.

The project also introduces several technological innovations in optical sensing techniques. A key challenge in using DAS for tsunami and large- earthquake monitoring is its sensitivity to long-period signals. While DAS has successfully detected oceanographic phenomena like tides and gravity waves, its sensitivity typically decreases for the long periods’ characteristic of tsunami waves (>100 s). Moreover, DAS strain-rate data can become saturated for very large earthquakes, limiting its capability for magnitude estimation. To overcome these challenges, FERMAT will focus on advancing sensor technology, improving strain sensitivity, long-term stability, and dynamic strain range detection. In particular, we will explore CP-OTDR technology, which offers improved sensitivity and stability compared to traditional DAS systems, making it a promising alternative for offshore earthquake and tsunami monitoring.

In addition to hardware improvements, the project will develop advanced signal processing and interrogation techniques to optimize DAS performance for low-frequency seismic and tsunami waves, as well as large earthquake detection and characterization. These advancements will push the limits of fiber-optic sensing, expanding its applicability for real-time offshore hazard detection.

By integrating DAS into operational tsunami warning systems, FERMAT contributes to the modernization of seismic and oceanographic monitoring infrastructure, demonstrating the potential of fiber-optic technology to enhance early-warning capabilities. This project represents a major step toward a more resilient hazard detection system, leveraging pre-existing telecom infrastructure for cost-effective and scalable deployment. The expected outcomes will also pave the way for future global applications of DAS in earthquake and tsunami early warning.