J. Eur. Opt. Society-Rapid Publ. 2026, 22, 11 Ó The Author( s), published by EDP Sciences, 2026 https:// doi. org / 10.1051 / jeos / 2026007 Available online at: https:// jeos. edpsciences. org
EOSAM 2025 Guest editors: Omar El Gawhary, Stefan Witte, Ignacio Moreno
Journal of the European Optical Society-Rapid Publications
SHORT COMMUNICATION
Comparison of seismic records obtained by distributed acoustic sensing and ocean bottom seismometers
Orlando Frazão 1,*
, Susana Silva 1, Carlos Corela 2, Afonso Loureiro 2, 3, Susana Gonçalves 2, Paulo Robalinho 1, Ricardo Sousa 1, Hugo F. Martins 4, Fernando Carrilho 5, Rachid Omira 5, Manfred Niehus 6, 7, and Luis Matias 2 1 INESC TEC – Institute for Systems and Computer Engineering, Technology and Science, Rua do Campo Alegre, 687, 4150-179 Porto, Portugal 2 Instituto Dom Luiz, University of Lisbon, 1749-016 Lisbon, Portugal 3 Agência Regional para o Desenvolvimento da Investigação, Tecnologia e Inovação, Funchal, Portugal 4 Instituto de Óptica“ Daza de Valdés” IO-CSIC, C / Serrano 121, 28006 Madrid, Spain 5 Instituto Português do Mar e da Atmosfera, Rua C ao aeroporto, 1749-077 Lisbon, Portugal 6 IT Instituto de Telecomunicações Lisboa, Campus Alameda, Torre Norte- Piso 10, Av. Rovisco Pais, 1, 1049- 001 Lisboa, Portugal 7 ISEL Instituto Superior de Engenharia de Lisboa, Rua Conselheiro Emídio Navarro 1, 1959-007 Lisboa, Portugal
Received 3 December 2025 / Accepted 23 January 2026
Abstract. This work presents an experimental framework for offshore seismic monitoring that combines Distributed Acoustic Sensing( DAS) with ocean-bottom seismometers( OBS). The study was conducted in the Azores region – Faial, where an HDAS interrogator prototype was connected to dark fiber submarine fiber-optic cable, complemented by the installation of two Ocean Bottom Seismometers( OBS) for calibration and validation of DAS technology. The main objective is to demonstrate that seismic observations obtained by DAS from seafloor cables can provide essential information similar to OBS and particularly in areas where land-based monitoring stations are limited.
Keywords: Distributed acoustic sensing, Submarine cable, Ocean-bottom seismometers, Sismology.
1 Introduction
Distributed Acoustic Sensing( DAS) enables fiber-optic cables to be used as dense, distributed arrays of acoustic sensors via a simple OTDR-based approach, offering clear advantages in marine environments where conventional instrumentation is difficult to deploy [ 1 ]. Because the fiber acts simultaneously as the sensing element and the transmission medium, and its optical properties respond to external disturbances, careful validation and calibration are required for quantitative applications such as earthquake magnitude estimation [ 2 ]. DAS has been successfully used for detecting and locating earthquakes, imaging subsurface structure, and monitoring natural hazards, with recent studies extending its use to hypocenter estimation, magnitude proxies, and rupture characterization from strain / strain-rate data [ 3 ]. Typical sensing ranges lie between 30 – 40 km and 100 km, limited by fiber attenuation and Rayleigh backscatter degradation [ 4 ]. Distributed Raman amplification can extend the range beyond 100 km [ 5 ], and with the use of pulse compression it can reach distances of
* Corresponding author: orlando. frazao @ inesctec. pt
> 150 km [ 6 ]. Ocean Bottom Seismometers( OBS) are autonomous platforms that record ground motion on the seafloor, enabling offshore seismicity monitoring and lithospheric studies in areas lacking land networks. They typically integrate a 3-component broadband seismometer and a hydrophone, improving the separation of seismic, hydrodynamic, and acoustic signals [ 7 ]. In this work, we describe the experimental framework for monitoring using both DAS and OBS. We then summarize the main properties of the DAS and OBS datasets and discuss preliminary earthquake analyses as recorded by both systems. Finally, we demonstrate that in regions such as the Azores – Faial where seismic monitoring is largely restricted to land stations – DAS observations from offshore cables can provide valuable information for real-time operations and for deferred-time investigations of offshore seismicity.
2 Installation of the HDAS and OBS on the submarine cable
The submarine cable used in this study comprises three fiber pairs of standard single-mode optical fiber( SMF-28).
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