A Prototypal DAS-Based Earthquake Early Warning System Offshore Chile

Distributed Acoustic Sensing (DAS) transforms fibre-optic cables into densely spaced arrays of strain sensors, providing metre-scale resolution over distances of up to hundreds of kilometres. By analysing interferometric backscatter from laser pulses, DAS measures deformation rate along the fibre, yielding single-component recordings of longitudinal strain.

In seismology, DAS supports both high-resolution imaging and seismic monitoring. Its dense sampling enables regional tomography and detailed characterization of shallow structures, while coherent travel-time data can be integrated into standard processing workflows. Phase picking can be performed using adapted artificial intelligence methods for continuous data, although earthquake location remains challenging due to cable geometry. Nevertheless, DAS observations allow for source characterization, including magnitude and source parameter estimation, and in some cases focal mechanism determination.

Beyond offline applications, DAS shows strong potential for real-time monitoring, particularly for Earthquake Early Warning (EEW). Its integration into operational systems requires tailored strategies to exploit dense spatial sampling and to address system-specific features such as directional sensitivity and strain-rate saturation.

Here, we evaluate the applicability of EEW methodologies to DAS data using three interrogators from the ABYSS network in central Chile that sense 450km of offshore cables running parallel to the subduction trench. The region, characterized by frequent moderate-to-large earthquakes, provides an ideal testbed for assessing EEW performance and the potential for rapid alerting.

We develop a real-time magnitude estimation approach suited to offshore DAS conditions, where direct P-wave signals are often weak and followed in the first seconds by stronger arrivals of secondary phases, and integrate it into the QuakeUp algorithm. Performance is assessed using M≥4 events and 60 days of continuous data to evaluate both source characterization capability and robustness to false alerts and missed detections. Our results demonstrate the feasibility of a prototype DAS-based EEW system and highlight its potential to improve response times in high-seismicity regions.

Part of this work has been performed by the Transnational Access to the GeoAzur laboratory MAREA (Magnitude estimAtion in Real TimE using DAS) supported by the EU project Geo-INQUIRE. Geo-INQUIRE is funded by the European Commission under project number 101058518 within the HORIZON-INFRA-2021-SERV-01 call.