Anomalously large seismic amplifications in the seafloor area off the Kii peninsula

Takeshi Nakamura, Masaru Nakano, Naoki Hayashimoto, Narumi Takahashi, Hiroshi Takenaka, Taro Okamoto, Eiichiro Araki, Yoshiyuki Kaneda

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

Seismic wave amplifications were investigated using strong-motion data obtained from the ground’s surface (K-net) on the Kii peninsula (southwestern Japan) and from the network of twenty seismic stations on the seafloor (DONET) located off the peninsula near the Nankai trough. Observed seismograms show that seismic signals at DONET stations are significantly larger than those at K-net stations, independent of epicentral distances. In order to investigate the cause of such amplifications, seismic wavefields for local events were simulated using the finite-difference method, in which a realistic 3D velocity structure in and around the peninsula was incorporated. Our simulation results demonstrate that seismic waves are significantly amplified at DONET stations in relation to the presence of underlying low-velocity sediment layers with a total thickness of up to 10 km. Our simulations also show considerable variations in the degree of amplification among DONET stations, which is attributed to differences in the thickness of the sediment layers. The degree of amplification is relatively low at stations above thin sediment layers near the trough axis, but seismic signals are much more amplified at stations closer to the Kii peninsula, where sediment layers are thicker than those at the trough axis. Simulation results are consistent with observations. This study, based on seafloor observations and simulations, indicates that because seismic signals are amplified due to the ocean-specific structures, the magnitude of earthquakes would be overestimated if procedures applied to data observed at land stations are used without corrections.

Original languageEnglish
Pages (from-to)255-270
Number of pages16
JournalMarine Geophysical Research
Volume35
Issue number3
DOIs
Publication statusPublished - 2014

Fingerprint

peninsulas
Amplification
amplification
Sediments
seafloor
stations
Seismic waves
sediments
troughs
trough
seismic waves
Finite difference method
seismic wave
sediment
simulation
Earthquakes
wave amplification
station
seismograms
strong motion

Keywords

  • DONET
  • Earthquake early warning
  • Finite-difference method
  • Seafloor observation
  • Seismic wave propagation
  • Tonankai area

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Oceanography

Cite this

Nakamura, T., Nakano, M., Hayashimoto, N., Takahashi, N., Takenaka, H., Okamoto, T., ... Kaneda, Y. (2014). Anomalously large seismic amplifications in the seafloor area off the Kii peninsula. Marine Geophysical Research, 35(3), 255-270. https://doi.org/10.1007/s11001-014-9211-2

Anomalously large seismic amplifications in the seafloor area off the Kii peninsula. / Nakamura, Takeshi; Nakano, Masaru; Hayashimoto, Naoki; Takahashi, Narumi; Takenaka, Hiroshi; Okamoto, Taro; Araki, Eiichiro; Kaneda, Yoshiyuki.

In: Marine Geophysical Research, Vol. 35, No. 3, 2014, p. 255-270.

Research output: Contribution to journalArticle

Nakamura, T, Nakano, M, Hayashimoto, N, Takahashi, N, Takenaka, H, Okamoto, T, Araki, E & Kaneda, Y 2014, 'Anomalously large seismic amplifications in the seafloor area off the Kii peninsula', Marine Geophysical Research, vol. 35, no. 3, pp. 255-270. https://doi.org/10.1007/s11001-014-9211-2
Nakamura, Takeshi ; Nakano, Masaru ; Hayashimoto, Naoki ; Takahashi, Narumi ; Takenaka, Hiroshi ; Okamoto, Taro ; Araki, Eiichiro ; Kaneda, Yoshiyuki. / Anomalously large seismic amplifications in the seafloor area off the Kii peninsula. In: Marine Geophysical Research. 2014 ; Vol. 35, No. 3. pp. 255-270.
@article{7adade310e5c4aa0b4e696273dc652d3,
title = "Anomalously large seismic amplifications in the seafloor area off the Kii peninsula",
abstract = "Seismic wave amplifications were investigated using strong-motion data obtained from the ground’s surface (K-net) on the Kii peninsula (southwestern Japan) and from the network of twenty seismic stations on the seafloor (DONET) located off the peninsula near the Nankai trough. Observed seismograms show that seismic signals at DONET stations are significantly larger than those at K-net stations, independent of epicentral distances. In order to investigate the cause of such amplifications, seismic wavefields for local events were simulated using the finite-difference method, in which a realistic 3D velocity structure in and around the peninsula was incorporated. Our simulation results demonstrate that seismic waves are significantly amplified at DONET stations in relation to the presence of underlying low-velocity sediment layers with a total thickness of up to 10 km. Our simulations also show considerable variations in the degree of amplification among DONET stations, which is attributed to differences in the thickness of the sediment layers. The degree of amplification is relatively low at stations above thin sediment layers near the trough axis, but seismic signals are much more amplified at stations closer to the Kii peninsula, where sediment layers are thicker than those at the trough axis. Simulation results are consistent with observations. This study, based on seafloor observations and simulations, indicates that because seismic signals are amplified due to the ocean-specific structures, the magnitude of earthquakes would be overestimated if procedures applied to data observed at land stations are used without corrections.",
keywords = "DONET, Earthquake early warning, Finite-difference method, Seafloor observation, Seismic wave propagation, Tonankai area",
author = "Takeshi Nakamura and Masaru Nakano and Naoki Hayashimoto and Narumi Takahashi and Hiroshi Takenaka and Taro Okamoto and Eiichiro Araki and Yoshiyuki Kaneda",
year = "2014",
doi = "10.1007/s11001-014-9211-2",
language = "English",
volume = "35",
pages = "255--270",
journal = "Marine Geophysical Researches",
issn = "0025-3235",
publisher = "Springer Netherlands",
number = "3",

}

TY - JOUR

T1 - Anomalously large seismic amplifications in the seafloor area off the Kii peninsula

AU - Nakamura, Takeshi

AU - Nakano, Masaru

AU - Hayashimoto, Naoki

AU - Takahashi, Narumi

AU - Takenaka, Hiroshi

AU - Okamoto, Taro

AU - Araki, Eiichiro

AU - Kaneda, Yoshiyuki

PY - 2014

Y1 - 2014

N2 - Seismic wave amplifications were investigated using strong-motion data obtained from the ground’s surface (K-net) on the Kii peninsula (southwestern Japan) and from the network of twenty seismic stations on the seafloor (DONET) located off the peninsula near the Nankai trough. Observed seismograms show that seismic signals at DONET stations are significantly larger than those at K-net stations, independent of epicentral distances. In order to investigate the cause of such amplifications, seismic wavefields for local events were simulated using the finite-difference method, in which a realistic 3D velocity structure in and around the peninsula was incorporated. Our simulation results demonstrate that seismic waves are significantly amplified at DONET stations in relation to the presence of underlying low-velocity sediment layers with a total thickness of up to 10 km. Our simulations also show considerable variations in the degree of amplification among DONET stations, which is attributed to differences in the thickness of the sediment layers. The degree of amplification is relatively low at stations above thin sediment layers near the trough axis, but seismic signals are much more amplified at stations closer to the Kii peninsula, where sediment layers are thicker than those at the trough axis. Simulation results are consistent with observations. This study, based on seafloor observations and simulations, indicates that because seismic signals are amplified due to the ocean-specific structures, the magnitude of earthquakes would be overestimated if procedures applied to data observed at land stations are used without corrections.

AB - Seismic wave amplifications were investigated using strong-motion data obtained from the ground’s surface (K-net) on the Kii peninsula (southwestern Japan) and from the network of twenty seismic stations on the seafloor (DONET) located off the peninsula near the Nankai trough. Observed seismograms show that seismic signals at DONET stations are significantly larger than those at K-net stations, independent of epicentral distances. In order to investigate the cause of such amplifications, seismic wavefields for local events were simulated using the finite-difference method, in which a realistic 3D velocity structure in and around the peninsula was incorporated. Our simulation results demonstrate that seismic waves are significantly amplified at DONET stations in relation to the presence of underlying low-velocity sediment layers with a total thickness of up to 10 km. Our simulations also show considerable variations in the degree of amplification among DONET stations, which is attributed to differences in the thickness of the sediment layers. The degree of amplification is relatively low at stations above thin sediment layers near the trough axis, but seismic signals are much more amplified at stations closer to the Kii peninsula, where sediment layers are thicker than those at the trough axis. Simulation results are consistent with observations. This study, based on seafloor observations and simulations, indicates that because seismic signals are amplified due to the ocean-specific structures, the magnitude of earthquakes would be overestimated if procedures applied to data observed at land stations are used without corrections.

KW - DONET

KW - Earthquake early warning

KW - Finite-difference method

KW - Seafloor observation

KW - Seismic wave propagation

KW - Tonankai area

UR - http://www.scopus.com/inward/record.url?scp=84920258527&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=84920258527&partnerID=8YFLogxK

U2 - 10.1007/s11001-014-9211-2

DO - 10.1007/s11001-014-9211-2

M3 - Article

AN - SCOPUS:84920258527

VL - 35

SP - 255

EP - 270

JO - Marine Geophysical Researches

JF - Marine Geophysical Researches

SN - 0025-3235

IS - 3

ER -