Sea surface gravity waves excited by dynamic ground motions from large regional earthquakes

Yoshihiro Ito, Spahr C. Webb, Yoshihiro Kaneko, Laura M. Wallace, Ryota Hino

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3 Citations (Scopus)


Infragravity waves on the sea surface near coastlines are occasionally excited by static displacement caused by large local earthquakes and recorded as tsunamis. However, tsunamis induced by ground motions from seismic waves are rarely observed, especially far from earthquake focal areas. We investigated seafloor pressure variations in the infragravity band at the Hikurangi subduction zone following the M 7.8 Kaikōura and M 7.1 Te Araroa earthquakes. Anomalous infragravity waves were observed at 0.2-20 mHz at sites overlying a low-velocity accretionary wedge offshore of the east coast of New Zealand's North Island accompanying the Rayleigh-wave arrivals. The maximum amplitude of these ultra-low-frequency waves was similar to the tsunami that propagated from the earthquake focal area hours later. The amplitude of the pressure signal from these waves observed offshore varied inversely with water depth, suggesting that sea surface gravity waves were excited by Rayleigh or Love waves amplified within the accretionary wedge.

Original languageEnglish
Pages (from-to)2268-2277
Number of pages10
JournalSeismological Research Letters
Issue number4
Publication statusPublished - 2020 Jul 1

ASJC Scopus subject areas

  • Geophysics


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