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Analysis of Seismic Body-waves Observed on Multiple Spans of the Iris Subsea Fiber-optic Cable Connecting Iceland and Ireland

Description: 

About 70% of the Earth's surface is covered by ocean, making observations of seismic waves difficult and expensive in vast regions of the globe. Recently, seismic waves have been observed using transmission fiber-optic sensing on trans-oceanic subsea cables, making them an exciting potential addition to global seismic networks (f.ex. Marra 2018,2022; Zhan, 2021; Mazur 2024; 2025).

In this study we investigate the potential of using observations of seismic body-waves on subsea cables for quantitative seismological studies. We use a fiber optic sensing instrument prototype capable of measuring the integrated strain over each span between repeaters (typically 100 km) of a subsea cable, over its entire length.This way each span acts as an individual sensor, allowing for a separation of signals from different parts of the cable, leading to higher S/N ratios on quiet deep-water segments and more easily interpreted waveforms. The instrument recorded data on 17 spans of the IRIS subsea cable, which connects Iceland and Ireland, and operated from May 2024 - March 2025. During this time almost 300 earthquakes larger than M 5.5 occurred globally.

We attempt to pick P-waves for all events with M > 5.5 and at distances < 100° on all the spans. We compare the timing of the picks to predicted P-wave arrivals and investigate how the quality of the picks varies with observed frequency, subsea environment and back-azimuth relative to local cable orientation. Furthermore, we simulate the waveforms of the body-wave train, using the seismic wavepropagation software SPECFEM3D, and compare to observed data. We find that some phases are relatively well recovered whereas others are not, and discuss possible reasons for this difference.

Session: Fiber-Optic Sensing Applications in Seismology and Environmental Science - V

Type: Oral

Date: 4/17/2026

Presentation Time: 05:15 PM (local time)

Presenting Author: Vala Hjörleifsdóttir

Student Presenter: No

Invited Presentation: No

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