Does not seismic attenuation in the Earth really depend on ampligude??

• Project/Area Number: 20K20939
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 17:Earth and planetary science and related fields
• Research Institution: Tokyo Institute of Technology
• Principal Investigator: Nakajima Junichi 東京工業大学, 理学院, 教授 (30361067)
• Project Period (FY): 2020-07-30 – 2024-03-31
• Project Status: Completed (Fiscal Year 2023)
• Budget Amount: ¥6,500,000 (Direct Cost: ¥5,000,000、Indirect Cost: ¥1,500,000); Fiscal Year 2022: ¥1,950,000 (Direct Cost: ¥1,500,000、Indirect Cost: ¥450,000); Fiscal Year 2021: ¥1,430,000 (Direct Cost: ¥1,100,000、Indirect Cost: ¥330,000); Fiscal Year 2020: ¥3,120,000 (Direct Cost: ¥2,400,000、Indirect Cost: ¥720,000)
• Keywords: 地震波減衰 / スペクトル比 / 地震波スペクトル / 地震波 / 減衰

Outline of Research at the Start

固体地球の塑性変形や自由振動，潮汐応答などを定式化するために不可欠なパラメータに非弾性減衰(Q値)がある。Q値の周波数依存は多くの研究で調べられているが，入力振幅の依存性を調べた研究はない。本研究では地震波形解析により減衰の振幅依存性の有無を検証する。解析では，2011年東北地方太平洋沖地震後に発生したメカニズム解のよく似た多数の余震を用いることで，震源位置の近い地震を選択しつつ，地震の規模の差も担保する工夫する。

Outline of Final Research Achievements

This study investigates whether attenuation is actually independent of seismic-wave amplitudes by systematic analysis of a large number of spectral amplitudes of co-located earthquake pairs with different observed amplitudes. We analyzed M3-5 intraslab earthquakes that occurred after the 2003 Miyagi-oki earthquake (M7.1) in NE Japan. The obtained results suggest that amplitude-dependent attenuation is required to explain the observations, which contradicts a long-standing recognition that amplitude-dependent attenuation is negligible for the propagation of seismic waves. Our model calculation suggests that Q^(-1) is proportional to the seismic amplitude, A, with the power of 0.1-0.2. Our result highlights the need to revisit and potentially rethink current models of the physical mechanisms influencing intrinsic attenuation.

Academic Significance and Societal Importance of the Research Achievements

地震波の減衰は波の振幅に影響を与えるため，強震動の数値シミュレーションなどにも重要なパラメータである．しかしながら，これまでの研究では減衰は振幅に因らず一様であると仮定されてきた．もし減衰に振幅依存がある場合，強震動を正しく評価するためには，振幅依存を考慮する必要がある．特に強震動は振幅が大きいため，減衰の非線形性の影響をより強く受けるからである．本研究の結果は，大地震の地震動予測の高精度化に資すると考えられる．

Research Products

• [Journal Article] Temporal Variations in and Above a Megathrust Following Episodic Slow‐Slip Events (2023)
  • Author(s): Ito Yosuke、Nakajima Junichi
  • Journal Title: Geophysical Research Letters Volume: 50 Issue: 14 Pages: 1-9
  • DOI: 10.1029/2023gl103577
  • Peer Reviewed / Open Access
• [Journal Article] The Wakayama earthquake swarm in Japan (2023)
  • Author(s): Nakajima Junichi
  • Journal Title: Earth, Planets and Space Volume: 75 Issue: 1 Pages: 43-43
  • DOI: 10.1186/s40623-023-01807-6
  • Peer Reviewed / Open Access
• [Journal Article] Deep subduction of the Philippine Sea slab and formation of slab window beneath central Japan (2023)
  • Author(s): Miyazaki Kazuki、Nakajima Junichi、Suenaga Nobuaki、Yoshioka Shoichi
  • Journal Title: Earth, Planets and Space Volume: 75 Issue: 1 Pages: 93-93
  • DOI: 10.1186/s40623-023-01846-z
  • Peer Reviewed / Open Access
• [Journal Article] Seismic Constraint on the Fluid‐Bearing Systems Feeding Hakone Volcano, Central Japan (2020)
  • Author(s): Kashiwagi Hirokazu、Nakajima Junichi、Yukutake Yohei、Honda Ryou、Abe Yuki、Sakai Shin'ichi
  • Journal Title: Journal of Geophysical Research: Solid Earth Volume: 125 Issue: 11 Pages: 1-16
  • DOI: 10.1029/2020jb020341
  • Peer Reviewed / Open Access
• [Presentation] 地震波減衰の振幅依存性について (2023)
  • Author(s): 手老勇登・中島淳一
  • Organizer: JpGU2023年大会
• [Presentation] 東北地方太平洋沖地震後の地震波減衰の時間変化 (2023)
  • Author(s): 手老勇登・中島淳一
  • Organizer: 地震学会秋季大会
• [Presentation] Spectral analysis for precise estimation of seismic attenuation (2022)
  • Author(s): 中島淳一
  • Organizer: 日本地球惑星科学連合
• [Presentation] 地震波減衰の振幅依存性について (2022)
  • Author(s): 手老勇登・中島淳一
  • Organizer: 日本地球惑星科学連合
• [Presentation] 地震波減衰の振幅依存性について (2022)
  • Author(s): 手老勇登・中島淳一
  • Organizer: 日本地震学会秋季大会