Earth-scale precursors of the Kamchatka earthquake revealed via polarization monitoring in undersea Mediterranean optical fiber links

By tracking the polarization rotation vector in submarine optical cables carrying live traffic across the Mediterranean Sea, we unambiguously detected the signature of the recent Mw 8.8 Kamchatka earthquake in two independent optical links in the Mediterranean Sea. Moreover, distinct precursors of the earthquake were observed in multiple cables within the same region. Their distance of roughly 9000 km from the epicenter unequivocally indicates that the earthquake preparation was governed by Earth-scale processes, whose nature remains unknown. These results demonstrate the potential of submarine optical fiber links as highly sensitive geophysical observatories, opening new perspectives for understanding earthquake dynamics and developing future early warning systems. (c) 2026 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement