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Non-tidal oceanographic fluctuation characteristics recorded in DONET ocean-bottom pressure time series using principal component analysis
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  • Hideto Otsuka,
  • Yusaku Ohta,
  • Ryota Hino,
  • Tatsuya Kubota,
  • Daisuke Inazu,
  • Tomohiro Inoue,
  • Narumi Takahashi
Hideto Otsuka
Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai, Japan

Corresponding Author:hideto.otsuka.q6@dc.tohoku.ac.jp

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Yusaku Ohta
Tohoku University

Corresponding Author:yusaku.ohta.d2@tohoku.ac.jp

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Ryota Hino
Tohoku University

Corresponding Author:hino@tohoku.ac.jp

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Tatsuya Kubota
National Research Institute for Earth Science and Disaster Resilience

Corresponding Author:kubotatsu@bosai.go.jp

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Daisuke Inazu
Tokyo University of Marine Science and Technology

Corresponding Author:inazud@m.kaiyodai.ac.jp

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Tomohiro Inoue
Graduate School of Science, Kyoto University

Corresponding Author:inoue.tomohiro.48n@st.kyoto-u.ac.jp

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Narumi Takahashi
Japan Agency for Marine-Earth Science and Technology

Corresponding Author:narumi@jamstec.go.jp

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Ocean bottom pressure-gauge (OBP) records play an important role in seafloor geodesy, but oceanographic fluctuations in OBP data are a major source of noise in seafloor transient crustal deformation observations, including slow slip events (SSEs), so it is important to evaluate them properly. To extract the significant characteristics of the oceanographic fluctuations, we applied principal component analysis (PCA) to the 3-year Dense Oceanfloor Network System for Earthquakes and Tsunamis (DONET) OBP time series for 40 stations during 2016–2019. PCA can separate several oceanographic signals based on the characteristics of their spatial distributions, although transient tectonic signals could not be clearly confirmed from the observed pressure records. The higher-order modes of the principal component reflected the oceanographic variation along the sea depth, and we interpreted that they were caused by the strength or weakness and meandering of ocean geostrophic currents, based on a comparison to the global ocean model ECCO2 by “Estimating the Circulation and Climate of the Ocean” (ECCO) consortium. In addition, to evaluate the ability of PCA to separate transient crustal deformation from oceanographic fluctuations, we conducted a synthetic test assuming an SSE by rectangular faults. The assumed synthetic tectonic signal can be separated from the oceanographic signals and included in the principal component independently depending on its amplitude. We proposed a transient event-detection method based on the spatial distribution variation of a specific principal component with or without a tectonic signal. This method can detect transient tectonic signals larger than moment-magnitude scale MW 5.9 from OBP records.  
22 Jan 2023Submitted to ESS Open Archive
24 Jan 2023Published in ESS Open Archive