Ground motions on rocky, cliffed, and sandy shorelines generated by ocean waves

TitleGround motions on rocky, cliffed, and sandy shorelines generated by ocean waves
Publication TypeJournal Article
Year of Publication2013
AuthorsYoung A.P, Guza RT, Dickson M.E, O'Reilly W.C, Flick RE
JournalJournal of Geophysical Research-Oceans
Date Published2013/12
Type of ArticleArticle
ISBN Number2169-9275
Accession NumberWOS:000329926200018
Keywordsbeach; cliff; coast; coastal; island; nearshore; new-zealand; noise; platform; platforms; seismometer; wave impacts; wave loading

We compare ground motions observed within about 100m of the waterline on eight sites located on shorelines with different morphologies (rock slope, cliff, and sand beaches). At all sites, local ocean waves generated ground motions in the frequency band 0.01-40 Hz. Between about 0.01 and 0.1 Hz, foreshore loading and gravitational attraction from ocean swell and infragravity waves drive coherent, in-phase ground flexing motions mostly oriented cross-shore that decay inland. At higher frequencies between 0.5 and 40 Hz, breaking ocean waves and wave-rock impacts cause ground shaking. Overall, seismic spectral shapes were generally consistent across shoreline sites and usually within a few orders of magnitude despite the diverse range of settings. However, specific site response varied and was influenced by a combination of tide level, incident wave energy, site morphology, ground composition, and signal decay. Flexing and shaking increased with incident wave energy and was often tidally modulated, consistent with a local generation source. Flexing magnitudes were usually larger than shaking, and flexing displacements of several mm were observed during relatively large incident wave conditions (Hs 4-5 m). Comparison with traffic noise and earthquakes illustrate the relative significance of local ocean-generated signals in coastal seismic data. Seismic observations are not a simple proxy for wave-cliff interaction.

Short TitleJ Geophys Res-Oceans
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