Tide‐Modulated Ocean‐to‐Earth Energy Conversion Quantified With Coastal Fiber Sensing

Abstract Quantifying how incident ocean waves transfer energy into seismic surface waves along the nearshore is essential for understanding coastal hazards and Earth–ocean coupling, yet time‐resolved in situ estimates have been scarce. Here we use a beach‐deployed distributed acoustic sensing array co‐located with an ocean‐bottom node to directly measure the conversion efficiency from wave impacts to Rayleigh‐type ground motion at 4–12 Hz. Frequency–wavenumber analysis, beamforming, and local back‐projection consistently locate sources along a fixed, wave‐breaking coastal segment, while particle‐motion ellipticity confirms the Rayleigh character. Calibrating distributed acoustic sensing strain to ground velocity and combining nearshore wave energetics yields an energy‐conversion efficiency on the order of 10 −6 . The efficiency is strongly modulated by tide, with high‐tide conditions enhancing coupling even though the source region remains stationary. Our results establish a quantitative benchmark for dynamic ocean‐to‐Earth energy transfer at the land–sea interface and provide a generalizable framework for coastal monitoring using existing fiber infrastructure.