High-frequency seismic noise generated from breaking shallow water ocean waves and the link to time-variable sea states

Breaking waves in the nearshore are known to generate a significant amount of high-frequency (f > 5Hz) energy. We investigate the correlation between the spectrum of seismic energy and the local sea states. We deployed a single three-component broadband seismometer approximately 50m from the seashore and recorded continuously for approximately 10 days. Our observations show that during elevated sea states, and presumably larger breaking waves in the surf zone, the power spectral density of the wave-generated seismic energy shifts to lower frequencies and higher spectral amplitudes. This is similar to the observation that large plunging breakers generate 1-20Hz acoustic infrasound, suggesting that a significant portion of the infrasound couples into seismic energy at the water/sea floor interface. Based on our observations and previous models, it appears that the seismic spectrum is sensitive to the wave size but not sediment movement. Regardless, the correlation of the seismic spectral power to the height and period of ocean waves suggests that seismic observations can be used as a proxy for local sea states, which may have implications for seashore sediment transport.