Optical Interferometry-based seafloor cable Measurements for Rupture Imaging and Tsunami Signal Analysis in the Southwest Pacific

Optical interferometry on submarine fiber-optic telecommunication cables offers a transformative opportunity for offshore geohazard monitoring by providing continuous measurements of seafloor perturbation at useful intervals over trans-oceanic distances (Marra et al., 2022). We analyze a southwest Pacific subset of data from a section of the Southern Cross NEXT cable connecting Auckland (New Zealand) to Alexandria (Australia). Using only cable-based measurements, we image the seismic rupture kinematics of the 17 December 2024 Mw 7.3 Vanuatu earthquake, the largest seismic event recorded on this cable since its installation.

 

We analyze measurements of a section of cable more than 1,000 km in length and comprising 18 inter-repeater spans including the section that runs roughly parallel to the Vanuatu subduction zone and the adjoining section extending southward toward New Zealand. The earthquake produces clear and coherent arrivals in the optical frequency deviation recorded across multiple spans, with well-defined signatures visible in both time series and spectrograms. We first extract earthquake-related strain signals in the 0.1-0.3 Hz frequency band and apply the Multiple Signal Classification (MUSIC) back-projection technique to recover the source-time evolution of the rupture. The inferred rupture is predominantly bilateral and consistent with the USGS finite-fault solution, confirming that interferometric submarine cables can function as effective regional seismic arrays for rapid characterization of offshore earthquakes.

 

These results further demonstrate the capability of submarine fiber-optic cables to image earthquake rupture processes using high-frequency strain signals, providing valuable monitoring coverage, especially in instrumentally sparse regions such as the southwest Pacific. By resolving rupture kinematics directly, cable-based observations offer a pathway toward improved tsunami early-warning strategies that rely less on empirical magnitude–scaling relations, which are uncertain for large earthquakes. Planned upgrades of the interrogating laser will allow the performance of this approach to be assessed at lower frequencies, where cable-based observations may provide direct constraints on tsunami propagation and other long-period geophysical processes.