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Extracting near-field seismograms from ocean-bottom pressure gauge inside the focal area: application to the 2011 Mw 9.0 Tohoku-Oki earthquake
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  • Tatsuya Kubota,
  • Tatsuhiko Saito,
  • Hiroaki Tsushima,
  • Ryota Hino,
  • Yusaku Ohta,
  • Syuichi Suzuki,
  • Daisuke Inazu
Tatsuya Kubota
National Research Institute for Earth Science and Disaster Resilience

Corresponding Author:[email protected]

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Tatsuhiko Saito
National Research Institute for Earth Science and Disaster Resilience
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Hiroaki Tsushima
Meteorological Research Institute
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Ryota Hino
Tohoku University
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Yusaku Ohta
Tohoku University
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Syuichi Suzuki
Tohoku University
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Daisuke Inazu
Tokyo University of Marine Science and Technology
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Abstract

Recent studies have shown that ocean-bottom pressure gauges (OBPs) can record seismic waves in addition to tsunamis and seafloor permanent displacements, even if they are installed inside the focal area where the signals are extremely large. We developed a method to extract dynamic ground motion waveforms from near-field OBP data consisting of a complex mixture of various signals, based on an inversion analysis along with a theory of tsunami generation. We applied this method to the OBP data of the 2011 Tohoku-Oki earthquake. We successfully extracted the low-frequency vertical seismograms inside the focal area (f < ~0.05 Hz), although those of the Mw ~9.0 megathrust earthquake had never previously been reported. The seismograms suggested two dominant energy releases around the hypocenter. The seismic wave signals recorded by the near-field OBP will be important not only to reveal earthquake ruptures and tsunami generation processes but also to conduct real-time tsunami forecasts.
16 Apr 2021Published in Geophysical Research Letters volume 48 issue 7. 10.1029/2020GL091664