Monitoring megathrust faults with abyssal distributed acoustic sensing

Project Information

ABYSS

Grant agreement ID: 101041092

DOI

10.3030/101041092

EC signature date 5 May 2022

Start date 1 October 2022

End date 30 September 2027

Funded under

• European Research Council (ERC)

Total cost

€ 2 134 970,00

EU contribution

€ 2 134 970,00

Coordinated by

OBSERVATOIRE DE LA COTE D'AZUR (OCA)
France

Periodic Reporting for period 1 - ABYSS (Monitoring megathrust faults with abyssal distributed acoustic sensing)

Reporting period: 2022-10-01 to 2025-03-31

Summary of the context and overall objectives of the project

Earthquakes have caused more than half a million of fatalities in the past 20 years. A large fraction of this death toll arises from the current lack of systematic predictive signals. While some theories suggest earthquakes are inherently unpredictable, evidence from laboratory and numerical experiments indicates they may be preceded by a preparatory phase. However, observations of this phase remain incomplete, mainly because extensive sensor networks cannot be deployed on the ocean floor near earthquake nucleation zones—particularly for large earthquakes most likely to produce precursors detectable at the surface.

The ABYSS project aims to address this gap by leveraging offshore fiber optic telecommunication cables along the Chilean subduction zone. By converting several ~100 km segments of these cables into a dense ocean-bottom seismic observatory, the project will generate unique data capable of detecting weak earthquakes and subtle changes in crustal properties with greater sensitivity, beyond the capabilities of onshore seismic networks. This transformative technology, combined with real-time data processing workflows, will enhance Chile’s early warning system by improving the timeliness and accuracy of earthquake warnings.

The project therefore has three key scientific goals: (1) to enhance sensitivity to small seismic events, particularly near the nucleation zones of large earthquakes; (2) to achieve high-resolution imaging of crustal structures and monitor changes over time; and (3) to develop a prototype fiber optic-based early warning system, paving the way for reliable earthquake detection and response mechanisms. The expected outcomes of this project will have a transformative impact on earthquake science as well as on the reduction of societal vulnerability to natural hazards.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The ABYSS project explores the use of offshore telecom fiber cables as underwater seismological observatories. Over two years, it implemented a system for real-time earthquake monitoring in central Chile, using 30,000 sensing points along 450 km of fiber optic cables. This approach has improved sensitivity to offshore seismic activity and supported earthquake monitoring with advanced data streaming technologies.

A central development of the project is an automated seismic monitoring platform for central Chile. This platform processes real-time data to detect, locate, and characterize earthquakes, forming the basis for a future earthquake early warning system. Each day, hundreds of seismic events detected and characterized by the ABYSS network are displayed on the dedicated website. The project has also created specialized workflows for DAS data, powered by the open-source Python library XDAS, which we developed to enable efficient DAS data management.

The project has also tested the potential of distributed acoustic sensing (DAS) technology for early warning systems. DAS offers high spatial resolution offshore, allowing faster detection and magnitude estimation compared to traditional onshore networks. While challenges such as signal saturation for large earthquakes remain, scaling relationships and magnitude estimation methods are being developed to address these limitations. These efforts contribute to improving earthquake monitoring and early warning capabilities.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Efforts have focused on building an offshore seismological observatory in central Chile using underwater telecom cables, enabling the observation of seismicity and offshore processes where our knowledge has been limited due to the lack of instrumentation. Building such infrastructure represents an important breakthrough, and its development is progressing well.

Thanks to this infrastructure and unprecedented spatial resolution, we have already highlighted the spatial variation in sediment coverage—a major feature that profoundly impacts seismic waveforms—which has been observed and characterized for the first time. With a better understanding of near-surface effects on seismic signals, we can now correct for these effects and obtain a clearer view of the earthquake source signatures.
Over the past year, continuous recordings on three cables, each spanning 150 km, have captured several local events with magnitudes greater than 6. These measurements have improved our understanding of the method's limitations for early warning systems and identified potential strategies to mitigate these challenges.

image-pour-rapport-intermediaire-erc.png