Source characteristics of ocean infragravity waves in the Philippine Sea: analysis of 3-year continuous network records of seafloor motion and pressure

Abstract

Continuous 3-year records of broadband ocean-bottom seismometers and pressure gauges of the seafloor network (Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET)) in the Nankai Trough region made it possible to monitor incoming ocean infragravity (IG) waves. Application of a slant-stacking technique revealed that the most energetic IG waves are incoming across the Nankai Trough from the Philippine Sea with limited energy of reflected waves back from the nearest coast. The sources of the most energetic waves are narrowly and stably localized into two closely adjacent azimuthal windows with mutually different wave spectral characteristics. Both sources show a seasonal variation, weak in summer and strong in winter. Although less energetic, IG waves propagating parallel to the trough and coast are observed. Such waves are greatly amplified when IG waves from a distant typhoon are incoming to the trough, suggesting the secondary origin of IG waves that can emit even more energetic waves than the originally incoming waves.

Excitation Location and Seasonal Variation of Transoceanic Infragravity Waves Observed at an Absolute Pressure Gauge Array

“…IGW characteristics in shallow waters have been investigated by sufficient observations on continental shelves (Herbers et al, 1995a(Herbers et al, , 1995bMunk, 1949;Thomson et al, 2007;Tucker, 1950). Although the temporal and spatial variations of IGWs in deep waters remain elusive due to a lack of deep-seafloor observations, their characteristics have been steadily revealed by previous studies (e.g., Dolenc et al, 2005;Sugioka et al, 2010;Tono et al, 2014;Webb et al, 1991). Webb et al (1991) identified the excitation locations of IGWs observed at an array deployed off California as originating from the Gulf of Alaska, the northwestern Pacific, and the southern tip of South America in boreal winter, by estimating the incoming direction of the transoceanic IGWs and assuming their great-circle path propagations.…”

Detection of Ocean Internal Tide Source Oscillations on the Slope of Aogashima Island, Japan

“…To analyze each 28‐day‐long record, we prepared eight consecutive segments, each consisting of a 7‐day‐long record, with mutual overlaps of 3.5 days. We band‐pass filtered each segment in the semidiurnal band (1.8 × 10 −5 –2.6×10 ‐5 Hz) and resampled at a rate of 40 s. Slowness vector analysis was performed for each segment (Nishida et al, ; Rost & Thomas, ; Tonegawa et al, ; Tono et al, ) to retrieve the semidiurnal internal tidal signal.…”

Ambient seismic wave field

“…Array analysis of ocean-floor pressure gauges in the deep sea record such propagation from coasts exposed by storms. 154 , 161 , 162 ) These leaky waves can travel across oceans with typical durations of several days. 163 ) The typical amplitudes observed for leaky waves are 5–10 mm, 164 ) although these amplitudes show seasonal variations.…”