Research on solid earth physics in the sub-millihertz band using a long-baseline laser strainmeter network

• Project/Area Number: 17H06207
• Research Category: Grant-in-Aid for Challenging Research (Pioneering)
• Allocation Type: Single-year Grants
• Research Field: Earth and planetary science and related fields
• Research Institution: The University of Tokyo
• Principal Investigator: Araya Akito 東京大学, 地震研究所, 教授 (30272503)
• Co-Investigator(Kenkyū-buntansha): 高森 昭光 東京大学, 地震研究所, 助教 (00372425) ; 小林 昭夫 気象庁気象研究所, 地震津波研究部, 室長 (20354532) ; 伊藤 武男 名古屋大学, 環境学研究科, 准教授 (40377982) ; 大久保 慎人 高知大学, 教育研究部自然科学系理工学部門, 准教授 (50462940) ; 勝間田 明男 気象庁気象研究所, 地震津波研究部, 室長 (80414514) ; 森井 亙 京都大学, 防災研究所, 助教 (30221633)
• Project Period (FY): 2017-06-30 – 2020-03-31
• Project Status: Completed (Fiscal Year 2020)
• Budget Amount: ¥25,870,000 (Direct Cost: ¥19,900,000、Indirect Cost: ¥5,970,000); Fiscal Year 2019: ¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000); Fiscal Year 2018: ¥4,550,000 (Direct Cost: ¥3,500,000、Indirect Cost: ¥1,050,000); Fiscal Year 2017: ¥17,160,000 (Direct Cost: ¥13,200,000、Indirect Cost: ¥3,960,000)
• Keywords: 歪計 / レーザー / 干渉計

Outline of Final Research Achievements

In this project, we have constructed a new network with laser strainmeters of three sites, Kamioka (Gifu Pref.), Inuyama (Aichi Pref.), and Funagira (Shizuoka Pref.), Japan, to observe accurate crustal deformation especially in the sub-millihertz band. The long-term strain data of Kamioka were consistent with regional tectonic trend observed by GNSS. We analyzed strain steps associated with local and distant earthquakes and found that all the observed amplitudes were the same order with theoretical strain steps calculated from fault models of the earthquakes while strain components of some sites were slightly different from the calculations. For the short-term slow slips which were sometimes observed in the Tokai area, records of Inuyama, Funagira, and borehole strainmeters were comprehensively analyzed and a very short-term, about an hour, acceleration of the slip was newly recognized.

Academic Significance and Societal Importance of the Research Achievements

本研究は、最先端のレーザー技術を用いて地面の動きを複数の地点で正確に捉え、従来の方法よりも周波数領域を広げ分解能を向上させ、さらに観測網を構築することで空間スケールを拡張した。研究期間内では観測網の構築と一部の記録の解析を行なったが、今後も高精度のレーザー干渉計を用いてサブミリヘルツ帯の歪を観測することにより、地震・火山現象と広域の歪蓄積過程との因果関係、地球中心核の密度構造と形状の知見と地球進化理論への制約、スロー地震の規模と継続時間に関するスケーリングの検証、など新たな発見や高い精度での仮説検証がもたらされることが期待される。

Research Products

• [Journal Article] Overview of KAGRA: Calibration, detector characterization, physical environmental monitors, and the geophysics interferometer (2021)
  • Author(s): A. Akutsu, H. Shinkai, KAGRA collaboration
  • Journal Title: Progress of Theoretical Experimental Physics Volume: ptab018 Issue: 5 Pages: 1-33
  • DOI: 10.1093/ptep/ptab018
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] 大型低温重力波望遠鏡KAGRAと地殻ひずみ計 (2020)
  • Author(s): 新谷昌人
  • Journal Title: 地震学会広報誌「なゐふる」 Volume: 121 Pages: 4-5
• [Journal Article] Design and operation of a 1500-m laser strainmeter installed at an underground site in Kamioka, Japan (2017)
  • Author(s): Araya Akito , Takamori Akiteru , Morii Wataru , Miyo Kouseki , Ohashi Masatake , Hayama Kazuhiro , Uchiyama Takashi , Miyoki Shinji , Saito Yoshio
  • Journal Title: Earth, Planets and Space Volume: 69 Issue: 1 Pages: 77-77
  • DOI: 10.1186/s40623-017-0660-0
  • Peer Reviewed / Open Access
• [Journal Article] Construction of KAGRA: an underground gravitational-wave observatory (2017)
  • Author(s): KAGRA Collaboration、ほか
  • Journal Title: Progress of Theoretical and Experimental Physics Volume: 2018 Issue: 1 Pages: 1-23
  • DOI: 10.1093/ptep/ptx180
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Presentation] Broadband observation of crustal activities using a laser-strainmeter network (2020)
  • Author(s): Akito Araya
  • Organizer: JpGU - AGU Joint Meeting 2020
  • Int'l Joint Research
• [Presentation] Slow slips with durations between VLF and short-term SSE (2020)
  • Author(s): Akio Katsumata
  • Organizer: JpGU - AGU Joint Meeting 2020
  • Int'l Joint Research
• [Presentation] Seismic and geodetic observation using a 1500-m laser strainmeter at an underground site in Kamioka (2018)
  • Author(s): Akito Araya
  • Organizer: International Workshop on Gravitomagnetism and Large-Scale Rotation Measurement, Wuhan Institute of Physics and Mathematics (WIPM), Chinese Academy of Sciences, June 6-10, 2018, Wuhan, China
  • Int'l Joint Research / Invited
• [Presentation] Long-baseline laser strainmeter constructed at the underground KAGRA site in Kamioka as a new tool for monitoring crustal dynamics (2017)
  • Author(s): A. Araya, A. Takamori, W. Morii, K. Miyo, and M. Ohashi
  • Organizer: IAG-IASPEI 2017
  • Int'l Joint Research