顔写真

キド　モトユキ
木戸　元之
Motoyuki Kido
所属
災害科学国際研究所　災害評価・低減研究部門　海域地震学研究分野
職名
教授
学位

  • 博士（理学）（東京大学）

  • 修士（理学）（東京大学）

学歴 1

  • 東京大学　大学院理学系研究科

    ～ 1996年3月

委員歴 2

  • 日本測地学会　評議員

    2013年5月 ～ 継続中

  • 日本測地学会　評議員

    2013年5月 ～ 継続中

所属学協会 3

  • 米国地球物理連合

  • 日本測地学会

  • 日本地震学会

研究キーワード 1

  • 海底測地学

研究分野 1

  • 自然科学一般 / 固体地球科学 /

論文 78

  1. The Anticipated Nankai Trough Earthquake and Tsunami in Japan: Determinant Factors of Residents’ Pre-Event Evacuation Intentions

    Kanan Hirano, Yo Fukushima, Hiroaki Maruya, Motoyuki Kido, Motoaki Sugiura

    Journal of Disaster Research　18　(3)　233-245　2023年4月1日

    出版者・発行元：Fuji Technology Press Ltd.

    DOI： 10.20965/jdr.2023.p0233 　

    ISSN：1881-2473

    eISSN：1883-8030

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    As a countermeasure against M8–9 class Nankai Trough earthquakes, the Japan Meteorological Agency started a service to release “Nankai Trough Earthquake Extra Information (Megathrust Earthquake Alert).” This alert is released after an M8.0 or higher earthquake occurs and the possibility of a subsequent earthquake is evaluated to be higher than usual. This is an innovative attempt at disaster mitigation in Japan as it encourages residents in the predefined area to pre-evacuate for one week when tsunami risk is higher. However, the factors influencing the evacuation behavior of residents are unknown. In this study, we investigated factors contributing to residents’ pre-event evacuation intentions using the hierarchical multiple regression analysis. We focused on the extent to which the recognition of the hazards and risks of the Nankai Trough earthquake and the response to the Extra Information, which are changeable by the local governments’ public relations activities, contributed to pre-event evacuation intentions after controlling for disaster-related general attitude and sociodemographic factors. Further, we paid special attention to residents’ degree of recognition of this information by checking the accuracy of their understanding of whether they lived within the pre-event evacuation area. The results showed that the recognition factors were relevant but less so than the general attitude toward disaster and more so than the sociodemographic factors. In addition, residents’ recognition accuracy was low. Our results suggest that it is important for local governments to make adequate efforts to encourage residents to evacuate.

  2. An approximate travel time calculation and a robust GNSS-acoustic positioning method using an MCMC technique

    Fumiaki Tomita, Motoyuki Kido

    Earth, Planets and Space　74　(1)　2022年12月2日

    出版者・発行元：Springer Science and Business Media LLC

    DOI： 10.1186/s40623-022-01740-0 　

    eISSN：1880-5981

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    Abstract It is important to consider horizontal heterogeneity in an underwater sound speed structure to accurately estimate positions of GNSS-acoustic sites. Although large amounts of moving survey data (a sea-surface platform moves around when acoustic signals are transmitted) are required to accurately detect a sloping sound speed structure, the actual observational data do not necessarily include sufficient moving survey data due to sea conditions or observational time. To treat these insufficient data, it was assumed that a shallow sound speed gradient was continuously present up to a fixed water depth (gradient depth). However, the validity of this assumption has not been investigated, and the gradient depth has not been optimized. In this study, we developed a new GNSS-acoustic array positioning method that optimizes the gradient depth using an MCMC technique. To employ this technique, we also developed an approximate technique for rapidly calculating travel time, because the conventional travel time calculation requires high computational cost for integration into the MCMC technique. We assessed the performance of the approximate travel time calculation technique and demonstrated its sufficient accuracy and precision for estimating array positions. Then, we applied the new GNSS-acoustic array positioning method to the actual observational data collected by the Japan Coast Guard and Tohoku University. Using enough amounts of the moving survey data, our method demonstrated the results comparable with the conventional GNSS-acoustic positioning method estimating a sloping sound speed structure; thus, the assumption of the sound speed gradient with the fixed water depth was valid. Moreover, due to the physical restriction of this assumption, our method provided robust solutions even when the observational data contained small quantities of moving survey data with a simple sea-surface track. Although our method still cannot be used in the scenario, where no moving survey data are available, it can work robustly compared with the conventional methods. Graphical Abstract

  3. Impact of employing a waveglider on GNSS-Acoustic survey along the Japan trench

    Motoyuki Kido, Chie Honsho, Fumiaki Tomita, Yusaku Ohta, Ryota Hino, Takeshi Iinuma

    2022年3月27日

    出版者・発行元：Copernicus {GmbH}

    DOI： 10.5194/egusphere-egu22-2138 　

  4. GNSS-Acoustic Observations of Seafloor Crustal Deformation Using a Wave Glider

    Takeshi Iinuma, Motoyuki Kido, Yusaku Ohta, Tatsuya Fukuda, Fumiaki Tomita, Iwao Ueki

    Frontiers in Earth Science　9　2021年3月11日

    出版者・発行元：Frontiers Media SA

    DOI： 10.3389/feart.2021.600946 　

    eISSN：2296-6463

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    Crustal deformation of the seafloor is difficult to observe solely using global navigation satellite system (GNSS). The GNSS-acoustic (GNSS-A) technique was developed to observe seafloor crustal deformation, and it has produced a steady series of successful observations with remarkable results related to crustal deformation associated with huge earthquakes around the Japanese Islands. However, utilizing GNSS-A incurs very large financial and human costs as it requires the use of a research vessel as a surface platform and has a limited observation frequency, which is less than once a year at seafloor stations along the Japan Trench. To conduct frequent observations, an automatic GNSS-A data acquisition system was developed that operates via an unmanned surface vehicle (wave glider). The first observations using this system were performed at a seafloor station off Aomori Prefecture in July 2019. The wave glider was equipped with two GNSS antennas, an acoustic transducer, a microelectromechanical system gyroscope, and associated control and logging units. Data acquisition and autonomous activation of the seafloor stations were successfully executed by controlling the power supply to the payload via satellite communication with the wave glider. The glider rarely strayed off the configured course and the solar panels generated sufficient power to perform the observations although the weather was mostly cloudy. The GNSS-A data processing results show that the position of the station was determined with the same accuracy and precision as in previous observations performed using a research vessel.

  5. Improvement on spatial resolution of a coseismic slip distribution using postseismic geodetic data through a viscoelastic inversion 査読有り

    Fumiaki Tomita, Takeshi Iinuma, Yusaku Ohta, Ryota Hino, Motoyuki Kido, Naoki Uchida

    Earth, Planets and Space　72　(1)　2020年6月

    出版者・発行元：Springer Science and Business Media LLC

    DOI： 10.1186/s40623-020-01207-0 　

    ISSN：1343-8832

    eISSN：1880-5981

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    Obvious crustal deformation is observed during a postseismic period as well as a coseismic period associated with a large earthquake. Major mechanisms of transient postseismic deformation are known as afterslip and viscoelastic relaxation. Since the viscoelastic relaxation occurs as a response to a coseismic slip, postseismic deformation provides information on coseismic deformation through the viscoelastic response. However, most previous studies have not thoroughly utilized postseismic geodetic observational data for revealing coseismic slip behaviors. In this study, we developed a slip inversion method that simultaneously estimates coseismic slip and postseismic slip distributions from coseismic and postseismic geodetic observational data using viscoelastic Green’s function (viscoelastic inversion method). We investigated the performance of the viscoelastic inversion method via two synthetic tests: one assumed a strike–slip event along an inland fault, while the other assumed a dip–slip event along a plate interface in a subduction zone. Both synthetic tests demonstrated that when extensive postseismic observational data were given, the viscoelastic inversion method provided a superior spatial resolution of coseismic slip distributions compared to conventional elastic inversion distributions. We also applied the viscoelastic inversion method to co- and post-seismic deformations associated with the 2011 Tohoku-oki earthquake. The seafloor geodetic observational network of the off-Tohoku region has been widely extended after the occurrence of the mainshock. Using this extended seafloor geodetic observational data, we successfully improved the spatial resolution of the coseismic slip distribution through the viscoelastic inversion method. Furthermore, using the seafloor observational data during the postseismic period, our inversion method enables us to obtain high spatial resolution of the coseismic slip in the offshore area and a reasonable coseismic slip distribution even if seafloor observational data during the coseismic period are unavailable. These results clarify the importance of deploying a geodetic observational network even after large coseismic events to assess past coseismic slip behaviors by considering the viscoelasticity of the Earth.[Figure not available: see fulltext.].

  6. Effects of disturbance of seawater excited by internal wave on GNSS-acoustic positioning

    R. Matsui, M. Kido, Y. Niwa, C. Honsho

    Marine Geophysical Research　40　(4)　541-555　2019年12月

    出版者・発行元：Springer Science and Business Media {LLC}

    DOI： 10.1007/s11001-019-09394-6 　

  7. Development of a kinematic GNSS-Acoustic positioning method based on a state-space model 査読有り

    Tomita, F, M. Kido, C. Honsho, R. Matsui

    Earth, Planets and Space　71　(102)　2019年9月

    DOI： 10.1186/s40623-019-1082-y 　

  8. Assessment of directional accuracy of GNSS-Acoustic measurement using a slackly moored buoy 査読有り

    Imano, M, M. Kido, C. Honsho, Y. Ohta, N. Takahashi, T. Fukuda

    Prog. Earth Planet. Sci.　6　(56)　1-14　2019年8月

    出版者・発行元：None

    DOI： 10.1186/s40645-019-0302-1 　

    eISSN：2197-4284

  9. Offshore Postseismic Deformation of the 2011 Tohoku Earthquake Revisited: Application of an Improved GPS-Acoustic Positioning Method Considering Horizontal Gradient of Sound Speed Structure 査読有り

    C. Honsho, M. Kido, F. Tomita, N. Uchida

    Journal of Geophysical Research: Solid Earth　124　(6)　5990-6009　2019年6月

    DOI： 10.1029/2018JB017135 　

    ISSN：2169-9313

    eISSN：2169-9356

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    ©2019. American Geophysical Union. All Rights Reserved. One of the important issues on the GPS-acoustic (GPS-A) observation for sea bottom positioning is how to address the horizontal heterogeneity of the sound speed in oceans. This study presents an analysis method of GPS-A data in the presence of a sloping sound speed structure. By applying this method and revising the analysis scheme to make full use of existing data, we reevaluated the horizontal postseismic deformations occurring ~1.5–5 years after the 2011 Tohoku earthquake. The revised horizontal movements have more uniform directions and rates between neighboring sites, suggesting enhancement of the array positioning accuracy. The revised displacement rate of the site on the incoming Pacific plate, located ~100 km northeast of the main rupture zone, was decreased significantly; it was only slightly, by 1.4 cm/year larger than the global motion of the Pacific plate, suggesting a relatively small effect of viscoelastic relaxation. The horizontal movements of the near-trench sites above the main rupture zone were generally landward and were significantly faster than the Pacific plate motion, indicating a viscoelastic relaxation of 5–10 cm/year. The distribution of the fast landward movements peaked near 38°N at an updip of the mainshock hypocenter and extended significantly farther to the north than to the south. This implies the existence of a secondary coseismic slip patch in the northern area in addition to a primary slip patch at ~38°N. The occurrence of episodic slow slip in early 2015 to the north of the main rupture zone was also verified from the GPS-A analyses.

  10. Seafloor geodesy revealed partial creep of the North Anatolian Fault submerged in the Sea of Marmara 査読有り

    Yamamoto R, M. Kido, Y. Ohta, N. Takahashi, Y. Yamamoto, A. Pinar, D. Kalafat, H. Özener, Y. Kaneda

    Geophys. Res. Lett.　46　(3)　1268-1275　2019年2月

    出版者・発行元：None

    DOI： 10.1029/2018GL080984 　

    ISSN：0094-8276

    eISSN：1944-8007

  11. A seismogeodetic amphibious network in the Guerrero Seismic Gap, Mexico

    Víctor M. Cruz-Atienza, Yoshihiro Ito, Vladimir Kostoglodov, Vala Hjörleifsdóttir, Arturo Iglesias, Josué Tago, Marco Calò, Jorge Real, Allen Husker, Satoshi Ide, Takuya Nishimura, Masanao Shinohara, Carlos Mortera-Gutierrez, Soliman García, Motoyuki Kido

    Seismological Research Letters　89　(4)　1435-1449　2018年7月

    DOI： 10.1785/0220170173 　

    ISSN：0895-0695

    eISSN：1938-2057

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    © 2018 Seismological Society of America. All rights reserved. The historical record of large subduction earthquakes in Guerrero, Mexico, reveals the existence of an 230-km length segment below the coast where no major rupture has occurred in the past 60 years. Reliable quantification of the hazard associated with such a seismic gap is urgently needed for risk mitigation purposes by means of state-of-the-art observations and modeling. In this article, we introduce and quantitatively assess the first seismogeodetic amphibious network deployed in Mexican and Central American soils that will provide the opportunity to achieve this goal in the near future. Deployed in 2017, the network is the result of a collaborative effort between Mexican and Japanese scientists. It consists of 15 onshore broadband and 7 ocean-bottom seismometers, 33 Global Positioning System (GPS) stations, 7 ocean-bottom pressure gauges, and 2 GPSacoustic sites,most of them installed within the Guerrero seismic gap. Initial data from the network revealed the occurrence of a 6-month-long slow-slip event in Guerrero, starting in May and ending in October 2017. To illustrate the performance of the various instruments, we also present the first ocean-bottom pressure and GPS-acoustic measurements in Mexico; the latter was obtained by means of an autonomousWave Glider vehicle. The ground motion of the devastating 19 September 2017 Mw 7.1 earthquake in central Mexico is presented as well. Nominal resolution of the seismogeodetic network is estimated through different synthetic inversion tests for tomographic imaging and the seismic coupling (or slow-slip) determination on the plate interface. The tests show that combined onshore and offshore instruments should lead to unprecedented results regarding the seismic potential (i.e., interface coupling) of the seismic gap and the Earth structure from the Middle America trench up to 70-km depth across the Guerrero state.

  12. Onboard realtime processing of GPS-acoustic data for moored buoy-based observation 査読有り

    Kido, M, M. Imano, Y. Ohta, T. Fukuda, N. Takahashi, S. Tsubone, Y. Ishihara, H. Ochi, K. Imai, C. Honsho, R. Hino

    J. Disaster Res.　13　(3)　472-488　2018年6月

    出版者・発行元：None

    DOI： 10.20965/jdr.2018.p0472 　

    ISSN：1881-2473

    eISSN：1883-8030

  13. Learning from crustal deformation associated with the M9 2011 Tohoku-oki earthquake 査読有り

    Wang Kelin, Sun Tianhaozhe, Brown Lonn, Hino Ryota, Tomita Fumiaki, Kido Motoyuki, Iinuma Takeshi, Kodaira Shuichi, Fujiwara Toshiya

    GEOSPHERE　14　(2)　552-571　2018年4月

    出版者・発行元：None

    DOI： 10.1130/GES01531.1 　

    ISSN：1553-040X

  14. A possible anorthositic continent of early Mars and the role of planetary size for the inception of Earth-like life

    Dohm, J.M., Maruyama, S., Kido, M., Baker, V.R.

    Geoscience Frontiers　9　(4)　2018年

    DOI： 10.1016/j.gsf.2016.12.003 　

  15. Seafloor geodetic observations to reveal co- and postseismic slip distributions of the 2011 Tohoku-Oki earthquake 査読有り

    Tomita, F, Y. Ohta, T. Iinuma, R. Hino, M. Kido, N. Uchida

    2018 OCEANS - MTS/IEEE Kobe Techno-Oceans (OTO)　1-4　2018年

    DOI： 10.1109/OCEANSKOBE.2018.8559370 　

  16. Along-trench variation in seafloor displacements after the 2011 Tohoku earthquake 査読有り

    Fumiaki Tomita, Motoyuki Kido, Yusaku Ohta, Takeshi Iinuma, Ryota Hino

    SCIENCE ADVANCES　3　(7)　e1700113　2017年7月

    出版者・発行元：AMER ASSOC ADVANCEMENT SCIENCE

    DOI： 10.1126/sciadv.1700113 　

    ISSN：2375-2548

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    The 2011 Tohoku-oki earthquake was the largest earthquake ever observed with seafloor geodetic techniques in and around its source region. Large crustal deformation associated with both the coseismic rupture and the rapid postseismic deformation has been reported. However, these observations are insufficient to describe the postseismic deformation processes occurring around the broad rupture area. We report the first results of seafloor Global Positioning System and acoustic ranging (GPS-A) observations based on repeated campaign surveys conducted over nearly 4 years using the extended GPS-A network deployed along the Japan Trench in September 2012. The observed postseismic displacement rates (DRs) show evident spatial variation along the trench: (i) distinct landward DRs in the large coseismic slip area [primary rupture area (PRA)], evidencing the predominance of viscoelastic relaxation; (ii) remarkable trenchward DRs in the south of the PRA, indicating rapid afterslip; and (iii) slight trenchward DRs in the north of the PRA. These features provide great insights into constructing a more complete model of viscoelastic relaxation, and they also indicate spatial variation of afterslip and fault locking along the plate interface with clear spatial resolution, providing invaluable information for the improvement of seismic hazard assessment.

  17. Comprehensive Analysis of Traveltime Data Collected Through GPS-Acoustic Observation of Seafloor Crustal Movements

    Honsho, C., Kido, M.

    Journal of Geophysical Research: Solid Earth　122　(10)　2017年

    DOI： 10.1002/2017JB014733 　

  18. Development and examination of new algorithms of traveltime detection in GPS/acoustic geodetic data for precise and automated analysis 査読有り

    Azuma, R., Tomita, F., Iinuma, T., Kido, M., Hino, R.

    Earth, Planets and Space　68　(1)　1-13　2016年8月11日

    DOI： 10.1186/s40623-016-0521-2 　

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    筆頭

  19. Extraction of crustal deformations and oceanic fluctuations from ocean bottom pressures Importance of integral studies combining seismology, ocean physics and tsunami engineering technology 査読有り

    Keisuke Ariyoshi, Hiroyuki Matsumoto, Takeshi Iinuma, Naoki Uchida, Akira Nagano, Takuya Hasegawa, Toshihiro Igarashi, Motoyuki Kido, Yusuke Yamashita

    OCEANS 2016 MTS/IEEE MONTEREY　2016年

    出版者・発行元：IEEE

    DOI： 10.1109/OCEANS.2016.7761035 　

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    DONET (Dense Oceanfloor Network system for Earthquakes and Tsunamis) has been developed and installed around Nankai Trough, which is motivated by the 2004 Sumatra-Andaman Earthquake. DONET contains pressure gauges as well as seismometers, which are expected to detect crustal deformations driven by peeling off subduction plate coupling process. From our simulation results, leveling changes are different sense among the DONET points even in the same science node. On the other hand, oceanic fluctuations such as melting ice masses through the global warming have so large scale as to cause ocean bottom pressure change coherently for all of DONET points especially in the same node. This difference suggests the possibility of extracting crustal deformations component from ocean bottom pressure data by differential of stacking data. However, this operation cannot be applied to local-scale fluctuations related to ocean mesoscale eddies and current fluctuations, which affect ocean bottom pressure through water density changes in the water column (from the sea surface to the bottom). Therefore, we need integral analysis by combining seismology, ocean physics and tsunami engineering so as to decompose into crustal deformation, oceanic fluctuations and instrumental drift, which will bring about high precision data enough to find geophysical phenomena.

  20. Seafloor observations indicate spatial separation of coseismic and postseismic slips in the 2011 Tohoku earthquake 査読有り

    Iinuma, T, R. Hino, N. Uchida, W. Nakamura, M. Kido, Y. Osada, S. Miura

    Nature Communications　7　2016年

    出版者・発行元：None

    DOI： 10.1038/ncomms13506 　

    ISSN：2041-1723

  21. A trial extraction of crustal deformation from seafloor hydraulic pressure gauges to estimate interplate coupling for subduction plate boundaries 査読有り

    Keisuke Ariyoshi, Akira Nagano, Takuya Hasegawa, Motoyuki Kido, Ryoko Nakata, Hiroyuki Matsumoto, Naoki Uchida, Toshihiro Igarashi

    Proceedings of the 12th SEGJ International Symposium, Tokyo, Japan, 18-20 November 2015　245-247　2015年11月20日

    出版者・発行元：Society of Exploration Geophysicists and Society of Exploration Geophysicists of Japan

    DOI： 10.1190/segj122015-079 　

  22. First measurement of the displacement rate of the Pacific Plate near the Japan Trench after the 2011 Tohoku-Oki earthquake using GPS/acoustic technique 査読有り

    Tomita, F., Kido, M., Osada, Y., Hino, R., Ohta, Y., Iinuma, T.

    Geophysical Research Letters　42　(20)　2015年10月28日

    DOI： 10.1002/2015GL065746 　

  23. GPS/Acoustic Measurement Using a Multi-purpose Moored Buoy System 査読有り

    Imano M, M. Kido, Y. Ohta, T. Fukuda, H. Ochi, N. Takahashi, R. Hino

    International Association of Geodesy Symposia　2015年8月

    DOI： 10.1007/1345_2015_192, 　

  24. Buoy Platform Development for Observation of Tsunami and Crustal deformation 査読有り

    Takahashi N, Y. Ishihara, T. Fukuda, H. Ochi, J. Tahara, T. Mori, M. Deguchi, M. Kido, Y. Ohta, R. Hino, K. Mutoh, G. Hashimoto, O. Motohashi, Y. Kaneda

    International Association of Geodesy Symposia　145　97-103　2015年3月

    DOI： 10.1007/1345_2015_114 　

    ISSN：0939-9585

  25. Investigation on the postseismic deformation associated with the 2011 Tohoku earthquake based on terrestrial and seafloor geodetic observations - to evaluate the further seismic hazard potential on the plate interface beneath the northeastern Japanese Isl 査読有り

    Iinuma T, R. Hino, M. Kido, Y. Osada, D. Inazu, Y. Ito, S. Suzuki, Y. Ohta, H Fujimoto

    International Association of Geodesy Symposia　2015年3月

    DOI： 10.1007/1345_2015_162 　

  26. Interplate Coupling in and Around the Rupture Area of the 2011 Tohoku Earthquake (M9.0) Before its Occurrence Based on Terrestrial and Seafloor Geodetic Observations 査読有り

    Iinuma T, R. Hino, M. Kido, Y. Ohta, S. Miura

    International Association of Geodesy Symposia　2015年3月

    DOI： 10.1007/1345_2015_48 　

  27. Achievement of the Project for Advanced GPS/Acoustic Survey in the Last Four Years 査読有り

    Kido M, H. Fujimoto, R. Hino, Y. Ohta, Y. Osada, T. Iinuma, R. Azuma, I. Wada, S. Miura, S. Suzuki, F. Tomita, M. Imano

    International Association of Geodesy Symposia　2015年3月

    DOI： 10.1007/1345_2015_127 　

  28. Improvement in the Accuracy of Real-Time GPS/Acoustic Measurements Using a Multi-Purpose Moored Buoy System by Removal of Acoustic Multipath

    Misae Imano, Motoyuki Kido, Yusaku Ohta, Tatsuya Fukuda, Hiroshi Ochi, Narumi Takahashi, Ryota Hino

    International Association of Geodesy Symposia　105-114　2015年

    出版者・発行元：Springer International Publishing

    DOI： 10.1007/1345_2015_192 　

    ISSN：0939-9585

    eISSN：2197-9359

  29. Progress in the Project for Development of GPS/Acoustic Technique Over the Last 4 Years 査読有り

    Kido, M, H. Fujimoto, R. Hino, Y. Ohta, Y. Osada, T. Iinuma, R. Azuma, I. Wada, S. Miura, S. Suzuki, F. Tomita, M, Imano

    International Association of Geodesy Symposia　2015年

  30. New buoy observation system for tsunami and crustal deformation 査読有り

    Narumi Takahashi, Yasuhisa Ishihara, Hiroshi Ochi, Tatsuya Fukuda, Jun'ichiro Tahara, Yosaku Maeda, Motoyuki Kido, Yusaku Ohta, Katsuhiko Mutoh, Gosei Hashimoto, Satoshi Kogure, Yoshiyuki Kaneda

    MARINE GEOPHYSICAL RESEARCH　35　(3)　243-253　2014年9月

    出版者・発行元：SPRINGER

    DOI： 10.1007/s11001-014-9235-7 　

    ISSN：0025-3235

    eISSN：1573-0581

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    We have developed a new system for real-time observation of tsunamis and crustal deformation using a seafloor pressure sensor, an array of seafloor transponders and a Precise Point Positioning (PPP ) system on a buoy. The seafloor pressure sensor and the PPP system detect tsunamis, and the pressure sensor and the transponder array measure crustal deformation. The system is designed to be capable of detecting tsunami and vertical crustal deformation of +/- 8 m with a resolution of less than 5 mm. A noteworthy innovation in our system is its resistance to disturbance by strong ocean currents. Seismogenic zones near Japan lie in areas of strong currents like the Kuroshio, which reaches speeds of approximately 5.5 kt (2.8 m/s) around the Nankai Trough. Our techniques include slack mooring and new acoustic transmission methods using double pulses for sending tsunami data. The slack ratio can be specified for the environment of the deployment location. We can adjust slack ratios, rope lengths, anchor weights and buoy sizes to control the ability of the buoy system to maintain freeboard. The measured pressure data is converted to time difference of a double pulse and this simple method is effective to save battery to transmit data. The time difference of the double pulse has error due to move of the buoy and fluctuation of the seawater environment. We set a wire-end station 1,000 m beneath the buoy to minimize the error. The crustal deformation data is measured by acoustic ranging between the buoy and six transponders on the seafloor. All pressure and crustal deformation data are sent to land station in real-time using iridium communication.

  31. Prevalence of viscoelastic relaxation after the 2011 Tohoku-oki earthquake 査読有り

    Sun T, K.Wang, T.Iinuma, R.Hino, J.He, H.Fujimoto, M.Kido, Y.Osada, S.Miura, Y.Ohta, Y.Hu

    Nature　514　(7520)　84-87　2014年9月

    出版者・発行元：None

    DOI： 10.1038/nature13778 　

    ISSN：0028-0836

    eISSN：1476-4687

  32. 海陸統合測地観測に基づく2011年東北地方太平洋沖地震に関する研究 査読有り

    藤本博己, 日野亮太, 木戸元之, 伊藤喜宏, 太田雄策, 飯沼卓史, 長田幸仁, 稲津大祐, 鈴木秀市, 佐藤俊也, 立花憲司, 出町知嗣, 三浦哲

    測地学会誌　60　(1)　1-22　2014年5月

    出版者・発行元：The Geodetic Society of Japan

    DOI： 10.11366/sokuchi.60.1 　

    ISSN：0038-0830

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    The geodetic research group of Tohoku University has been carrying out geodetic observations on shore and off shore of Miyagi Prefecture where earthquakes around M7.5 repeatedly occurred at intervals of about 40 years. We have been measuring horizontal movements of seafloor geodetic stations since 2003, using GPS-Acoustic （GPSA） seafloor positioning systems. We have also been continuously observing vertical crustal movements since 2008 using free-fall/pop-up ocean bottom pressure recorders （OBPRs）. Owing to these geodetic observations that were made in the region above the rupture area of the 2011 M9.0 Tohoku-oki earthquake, we succeeded in detecting unexpectedly large coseismic crustal displacements that had never been measured with geodetic systems on the seafloor. We retrieved data from the OBPRs that had been deployed above the rupture area, and to continue monitoring gradual postseismic slips, we installed replacements for these OBPRs at the same observation sites. We presented a model for the coseismic slip distribution on the plate boundary, and it is widely referenced because it is a model that is constrained by the OBPR data as well as the GPSA and the terrestrial geodetic data. We have also developed a method of real-time kinematic analyses of the data from a GNSS array to estimate the approximate magnitude of large earthquakes within several minutes. We developed a procedure to reduce tidal and non-tidal oceanic components in OBPR data. The pressure data analyzed jointly with onshore strain data revealed that there was a slow slip event near the focal zone about one month before the main event. The observed pressure variations also contain information about the coseismic and postseismic crustal movements associated with the M7.3 earthquake that occurred on March 9 and was estimated to be the largest foreshock. These results are important for clarifying geophysical processes that preceded the giant earthquake.

  33. Study of the 2011 off the pacific coast of Tohoku earthquake based on seafloor and terrestrial geodetic observation

    Fujimoto, H., Hino, R., Kido, M., Ito, Y., Ohta, Y., Iinuma, T., Osada, Y., Inazu, D., Suzuki, S., Sato, T., Tachibana, K., Demachi, T., Miura, S.

    Journal of the Geodetic Society of Japan　60　(1)　2014年

  34. Was the 2011 Tohoku-Oki earthquake preceded by aseismic preslip? Examination of seafloor vertical deformation data near the epicenter 査読有り

    Hino, R, D. Inazu, Y. Ohta, Y. Ito, S. Suzuki, T. Iinuma, Y. Osada, M. Kido, H. Fujimoto, Y. Kaneda

    Mar. Geophys. Res.　35　(3)　181-190　2013年12月

    出版者・発行元：None

    DOI： 10.1007/s11001-013-9208-2 　

    ISSN：0025-3235

    eISSN：1573-0581

  35. 衛星通信を活用したリアルタイムGPS解析 −地上通信障害時に地殻変動を実時間で把握するために− 査読有り

    山本淳平, 長田幸仁, 太田雄策, 平原 聡, 出町知嗣, 中山貴史, 立花憲司, 佐藤俊也, 木戸元之, 藤本博己, 日野亮太, 三浦 哲, 内田雅之

    測地学会誌　59　(4)　133-145　2013年10月

    出版者・発行元：The Geodetic Society of Japan

    DOI： 10.11366/sokuchi.59.133 　

    ISSN：0038-0830

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    The redundant communication pathway and processing strategy for satellite navigation system such as GPS is extremely important for more reliable quasi real-time crustal deformation monitoring in case of huge interplate earthquake occurrence. We tested real-time kinematic GPS processing (RTK-GPS) via satellite-based mobile phone for redundant communication pathway for address the vulnerabilities of the infrastructure. We succeed to get the stable time series via satellite mobile phone network with almost zero-missing data for short and long baseline RTK-GPS. We also assessed stability, precision and accuracy of StarFire<sup>TM</sup> global satellites based augmentation system for redundant processing strategy. In order to assess coordinate precision and accuracy, we compared 1Hz StarFire time series and post-processed precise point positioning (PPP) 1Hz time series by GIPSY-OASIS II processing software Ver. 6.1.2 with three different product types (ultrarapid, rapid, and final orbits). We also used different interval clock information (30 and 300 seconds) for the post-processed PPP processing. The standard deviation of real time StarFire time series is less than 30 mm (horizontal components) and 60 mm (vertical component) based on 1 month continuous processing. We also assessed noise spectrum of the estimated time series by StarFire and post-processed GIPSY PPP results. We found that the noise spectrum of StarFire time series is similar pattern with GIPSY-OASIS II processing result based on JPL rapid orbit products with 300 seconds interval clock information. Based on these stability and noise assessment, we suggest that the various communication pathways for RTK-GPS processing and various processing strategy such as global satellites based augmentation system with traditional RTK-GPS processing strategy is important for more reliable quasi real-time crustal deformation monitoring.

  36. Real time GPS processing utilizing satellite communications -Toward more reliable real-time crustal deformation monitoring under a situation of ground communication failure-

    Yamamoto, J., Osada, Y., Ohta, Y., Hirahara, S., Demachi, T., Nakayama, T., Tachibana, K., Sato, T., Kido, M., Fujimoto, H., Hino, R., Miura, S., Uchida, M.

    Journal of the Geodetic Society of Japan　59　(4)　2013年

  37. Seafloor geodesy: Its present state of affairs and future prospect

    Kido, M.

    Journal of the Geodetic Society of Japan　59　(3)　2013年

  38. Extended GPS/Acoustic geodetic observation near the Japan Trench axis for the study of the giant 2011 Tohoku-oki earthquake 査読有り

    H. Fujimoto, M. Kido, T. Iinuma, Y. Osada, J. Yamamoto, K. Tadokoro, M. Sato

    2013 IEEE INTERNATIONAL UNDERWATER TECHNOLOGY SYMPOSIUM (UT)　2013年

    出版者・発行元：IEEE

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    GPS/Acoustic seafloor geodetic observation played a key role to estimate the slip distribution of the 2011 giant Tohoku-oki earthquake. After the event, seismic coupling near the trench axis has been a focus to understand how such a huge earthquake occurs in a subduction zone. Observation of postseimic deformation is another and urgent task required in the Japan Trench. In order to realize these observations, we have newly installed 20 GPS/A observation sites extending some 400 km along the Japan Trench in September 2012. Precision acoustic transponders were newly developed to cope with the following three requirements: (1) observation on the deep seafloor, (2) compatibility among three institutions in Japan, and (3) observation for ten years.

  39. Episodic slow slip events in the Japan subduction zone before the 2011 Tohoku-Oki earthquake 査読有り

    Ito, Y, R. Hino, M. Kido, H. Fujimoto, Y. Osada, D. Inazu, Y. Ohta, T. Iinuma, M. Ohzono, S. Miura, M. Mishina, K. Suzuki, T. Tsuji, J. Ashi

    Tectonophysics　600　14-26　2013年

    出版者・発行元：None

    DOI： 10.1016/j.tecto.2012.08.022 　

    ISSN：0040-1951

    eISSN：1879-3266

  40. 海底地殻変動観測の現状と今後の展開 招待有り 査読有り

    木戸元之

    測地学会誌　59　(3)　99-109　2013年

    出版者・発行元：The Geodetic Society of Japan

    DOI： 10.11366/sokuchi.59.99 　

    ISSN：0038-0830

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    Seafloor geodetic measurements are now recognized as crucial tools to effectively monitor the crustal stress accumulation, especially after the Tohoku Earthquake 2011. The situation promotes the Japanese government to invest in facility of these tools to prepare for devastating disaster. Considering the rapid growth in this field, researchers must manage the tools as sustainable manner both in financial and human costs in order to maximize the efficiency for long-lasting operation. In this paper, current state of the seafloor geodesy and problems arose due to the drastic turn after the earthquake are addressed, then advocate how we should act toward the new era.

  41. Coseismic slip distribution of the 2011 off the Pacific Coast of Tohoku Earthquake (M9.0) refined by means of seafloor geodetic data 査読有り

    T. Iinuma, R. Hino, M. Kido, D. Inazu, Y. Osada, Y. Ito, M. Ohzono, H. Tsushima, S. Suzuki, H. Fujimoto, S. Miura

    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH　117　2012年7月

    出版者・発行元：AMER GEOPHYSICAL UNION

    DOI： 10.1029/2012JB009186 　

    ISSN：2169-9313

    eISSN：2169-9356

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    On 11 March 2011, the devastating M9.0 Tohoku Earthquake occurred on the interface of the subducting Pacific plate, and was followed by a huge tsunami that killed about 20,000 people. Several geophysical studies have already suggested that the very shallow portion of the plate interface might have played an important role in producing such a large earthquake and tsunami. However, the sparsity of seafloor observations leads to insufficient spatial resolution of the fault slip on such a shallow plate interface. For this reason, the location and degree of the slip has not yet been estimated accurately enough to assess future seismic risks. Thus, we estimated the coseismic slip distribution based on terrestrial GPS observations and all available seafloor geodetic data that significantly improve the spatial resolution at the shallow portion of the plate interface. The results reveal that an extremely large (greater than 50 m) slip occurred in a small (about 40 km in width and 120 km in length) area near the Japan Trench and generated the huge tsunami. The estimated slip distribution and a comparison of it with the coupling coefficient distribution deduced from the analysis of the small repeating earthquakes suggest that the 2011 Tohoku Earthquake released strain energy that had accumulated over the past 1000 years, probably since the Jogan Earthquake in 869. The accurate assessments of seismic risks on very shallow plate interfaces in subduction zones throughout the world can be obtained by improving the quality and quantity of seafloor geodetic observations.

  42. Trench-normal variation in observed seafloor displacements associated with the 2011 Tohoku-Oki earthquake 査読有り

    M. Kido, Y. Osada, H. Fujimoto, R. Hino, Y. Ito

    GEOPHYSICAL RESEARCH LETTERS　38　2011年12月

    出版者・発行元：AMER GEOPHYSICAL UNION

    DOI： 10.1029/2011GL050057 　

    ISSN：0094-8276

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    Seafloor geodetic measurements using the GPS/acoustic technique just above the rupture area of the 2011 Tohoku-Oki earthquake revealed strong trench-normal variation in the horizontal crustal displacement associated with the earthquake. One set of observations, at a site only 50 km away from the trench, yielded the most trench-ward data ever reported with an accuracy better than 1 m. It showed a coseismic displacement of up to 31 m, whereas another set of observations 100 km away from the trench showed a 15-m displacement. These horizontal data, as well as vertical data from pressure gauges and tsunami observations, strongly indicate that the seismic slip reached the trench. They are also likely to contribute quantitatively to further investigations that reveal the coseismic behavior of the frontal wedge of the overriding plate in the source region along the Japan Trench. Citation: Kido, M., Y. Osada, H. Fujimoto, R. Hino, and Y. Ito (2011), Trench-normal variation in observed seafloor displacements associated with the 2011 Tohoku-Oki earthquake, Geophys. Res. Lett., 38, L24303, doi: 10.1029/2011GL050057.

  43. Frontal wedge deformation near the source region of the 2011 Tohoku-Oki earthquake 査読有り

    Yoshihiro Ito, Takeshi Tsuji, Yukihito Osada, Motoyuki Kido, Daisuke Inazu, Yutaka Hayashi, Hiroaki Tsushima, Ryota Hino, Hiromi Fujimoto

    GEOPHYSICAL RESEARCH LETTERS　38　2011年8月

    出版者・発行元：AMER GEOPHYSICAL UNION

    DOI： 10.1029/2011GL048355 　

    ISSN：0094-8276

    eISSN：1944-8007

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    We report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 Tohoku-Oki earthquake. The uplift was measured by an ocean-bottom pressure gauge installed before the earthquake on a frontal wedge, which formed an uplift system near the Japan Trench. Horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake. The average displacements at the frontal wedge were 58 m east and 74 m east-southeast. These results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary. The estimated magnitude of the slip along the main fault was 80 m near the trench. Our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern Japan. Citation: Ito, Y., T. Tsuji, Y. Osada, M. Kido, D. Inazu, Y. Hayashi, H. Tsushima, R. Hino, and H. Fujimoto (2011), Frontal wedge deformation near the source region of the 2011 Tohoku-Oki earthquake, Geophys. Res. Lett., 38, L00G05, doi:10.1029/2011GL048355.

  44. Signal processing of acoustic ranging in GPS/Acoustic seafloor geodesy 査読有り

    M. Kido, H. Fujimoto, Y. Osada

    2011 IEEE Symposium on Underwater Technology, UT'11 and Workshop on Scientific Use of Submarine Cables and Related Technologies, SSC'11　2011年

    DOI： 10.1109/UT.2011.5774105 　

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    Acoustic signal processing is crucial for precise positioning of a seafloor transponder in GPS/Acoustic seafloor geodesy, which aims at 1 cm-precision. For this purpose, pseudorandom signals are usually employed for acoustic ranging. Considering the characteristics of the signal and the typical frequency of 10 kHz in carrier wave, detecting an arrival-time with 0.01 ms (∼0.75 cm) resolution in round trip can be readily achieved if the correct peak in correlogram is identified. However, due to sidelobes around the peak and pseudo peaks associated with possible multipath, a simple algorithm detecting the maximum peak often results in a wrong peak, which has a offset with a wavelength or larger from the correct peak. In our numerical study, behavior of the pseudo peak is found being quite complex having a no-integer wavelength offset when a short-range multipath is superimposed. Our observed data clearly show nadir-angle dependence in the appearance of received signals. This is attributed to significant change in the short-range multipath with angle within a sound-hood of a transducer as well as transducer characteristics itself. In this study, firstly we demonstrate the complexity in the behavior of the sidelobes with varying offset of multipath. Then, we analyze observed signal to reveal the angle-dependency of our transducer with different types of sound-hoods. © 2011 IEEE.

  45. Potential tsunamigenic faults of the 2011 off the Pacific coast of Tohoku Earthquake 査読有り

    Takeshi Tsuji, Yoshihiro Ito, Motoyuki Kido, Yukihito Osada, Hiromi Fujimoto, Juichiro Ashi, Masataka Kinoshita, Toshifumi Matsuoka

    EARTH PLANETS AND SPACE　63　(7)　831-834　2011年

    出版者・発行元：TERRA SCIENTIFIC PUBL CO

    DOI： 10.5047/eps.2011.05.028 　

    ISSN：1343-8832

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    Faults related to the tsunamigenic 2011 Tohoku-Oki Earthquake (M-w 9.0) were investigated by using multi-channel seismic reflection data acquired in 1999 and submersible seafloor observations from 2008. The location of the fault system interpreted in the seismic reflection profile is distributed around the area with largest slip and tsunami induction of the 2011 event. Cold-seep communities along the trace of the branch reverse fault and a high scarp associated with the trace of a normal fault suggest current activity on these faults. We interpret the fault system in the seismic profile as a shallow extension of the seismogenic fault that may have contributed to the resulting huge tsunami.

  46. Long-term stability of acoustic benchmarks deployed on thick sediment for GPS/acoustic seafloor positioning 査読有り

    Hiromi Fujimoto, Motoyuki Kido, Yukihito Osada, Keiichi Tadokoro, Takashi Okuda, Yoshihiro Matsumoto, Kozue Kurihara

    Modern Approaches in Solid Earth Sciences　8　263-272　2011年

    出版者・発行元：Springer International Publishing

    DOI： 10.1007/978-90-481-8885-7_13 　

    ISSN：1876-1682

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    GPS/Acoustic seafloor positioning has become an indispensable geodetic observation for the monitoring of crustal activities in subduction zones. There remain, however, some key problems to be settled. Among them is long-term stability of acoustic benchmarks deployed on the seafloor: long-term attitude stability, especially against ground motions of earthquakes, and their electrical/mechanical durability for long-term geodetic observation. M7-class earthquakes occurred in 2004 off Kii Peninsula, Central Japan, and then coseismic seafloor crustal movements were detected by using the GPS/Acoustic (GPS/A) observations. This event gave us a unique opportunity to test the stability. We carried out diving surveys in 2006 and visually inspected the benchmarks that detected the crustal movements. All of them stood stably on the flat sediment. No effects of the earthquakes were observed. In case that the slight tilts of the instruments were caused by the earthquakes, the effect on the observed crustal movements is estimated to be within 1 cm. One of old benchmarks deployed 6 years before was recovered and inspected. There was no problem on the battery, and no damages on the outer frame of the instrument. The diving surveys have settled a basic problem in seafloor geodesy and paved the way for long-term geodetic monitoring on the seafloor.

  47. 過去の海底地殻変動観測における動揺センサーデータの有効利用について 査読有り

    木戸元之, 藤本博己, 長田幸仁

    測地学会誌　54　(3)　2008年11月

    DOI： 10.11366/sokuchi1954.54.163 　

  48. Development of a seafloor acoustic ranging system toward the seafloor cable network system 査読有り

    Yukihito Osada, Motoyuki Kido, Hiromi Fujimoto, Yoshiyuki Kaneda

    OCEAN ENGINEERING　35　(14-15)　1401-1405　2008年10月

    出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

    DOI： 10.1016/j.oceaneng.2008.07.007 　

    ISSN：0029-8018

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    We have developed a seafloor acoustic ranging system as a possible future application to monitoring seafloor crustal movement with the DONET (Development of Dense Ocean-floor Network System for Earthquake and Tsunami) cabled observatory system. In 2007 we carried out an experiment for the seafloor acoustic ranging system. We deployed two precision acoustic transponders (PXPs) with about 750 m spacing in Kumano-nada at a water depth of about 2035 m. We collected 660 ranging data in this one-day experiment. The round-trip travel time shows a variation with peak-to-peak amplitude of about 25 mm in the range. It was confirmed that most of the variation could be explained by the change in sound speed estimated from measured temperature and pressure. The remaining fluctuation in the acoustic measurements is +/- 2 mm. (C) 2008 Elsevier Ltd. All rights reserved.

  49. GPS/acoustic seafloor geodetic observation - Major results and new approaches

    Sato, M., Kido, M., Tadokoro, K.

    Journal of the Geodetic Society of Japan　54　(3)　2008年

  50. Introduction of 10 Hz GPS receiver for the improved observation of seafloor crustal movement

    Osada, Y., Mizukami, T., Kido, M., Ohta, Y., Tsushima, H., Miura, S., Fujimoto, H.

    Journal of the Geodetic Society of Japan　54　(3)　2008年

  51. Development of a GPS/A positioning system on a moored buoy for continuous observation of seafloor crustal movements

    Fujimoto, H., Kido, M., Osada, Y., Kaneda, Y.

    Journal of the Geodetic Society of Japan　54　(3)　2008年

  52. 反射法地震探査および「しんかい6500」による観察から推定される日本海溝陸側斜面内断層

    辻 健, 伊藤 喜宏, 藤本 博巳, 木戸 元之, 芦 寿一郎, YK08-06 乗船研究者

    日本地質学会学術大会講演要旨　2008　171-171　2008年

    出版者・発行元：日本地質学会

    DOI： 10.14863/geosocabst.2008.0.171.0 　

    ISSN：1348-3935

  53. 過去の海底地殻変動観測における動揺センサーデータの有効利用について 査読有り

    木戸元之, 藤本博己, 長田幸仁

    測地学雑誌　54　(3)　163-179　2008年

    DOI： 10.11366/sokuchi1954.54.163 　

  54. GPS/音響測距結合方式による海底地殻変動観測 ～観測成果と新たな取り組み～ 査読有り

    佐藤まりこ, 木戸元之, 田所敬一

    測地学会誌　54　(3)　113-125　2008年

    出版者・発行元：日本測地学会

    DOI： 10.11366/sokuchi1954.54.113 　

    ISSN：0038-0830

  55. 10HzGPS受信機導入による海底地殻変動観測高度化の試み 査読有り

    長田幸仁, 水上知子, 木戸元之, 太田雄策, 対馬弘晃, 三浦 哲, 藤本博己

    測地学会誌　54　(3)　141-151　2008年

    DOI： 10.11366/sokuchi1954.54.141 　

  56. GPS/A方式海底地殻変動観測に向けた観測システムの開発 査読有り

    藤本博己, 木戸元之, 長田幸仁, 金田義之

    測地学会誌　54　(3)　181-187　2008年

    DOI： 10.11366/sokuchi1954.54.181 　

  57. Temporal variation of sound speed in ocean: a comparison between GPS/acoustic and in situ measurements 査読有り

    Motoyuki Kido, Yukihito Osada, Hiromi Fujimoto

    EARTH PLANETS AND SPACE　60　(3)　229-234　2008年

    出版者・発行元：TERRA SCIENTIFIC PUBL CO

    ISSN：1343-8832

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    The GPS/acoustic technique applied to seafloor geodesy intrinsically measures integrated sound speed along a trajectory of an acoustic signal as well as the position of a seafloor transponder array. We present here a generalized expression of sound speed variation in terms of a traveltime residual normalized to the vertical component. With this expression, residual traveltimes to any seafloor transponders will have a same value regardless of their depths and slant angles. This is valid even for the case having horizontal gradient in sound speed structure; the gradient affects only on positioning of a transponder array and not on the estimate of sound speed just beneath the observation point. We monitored temporal variation of this quantity through a GPS/acoustic survey and compared it with in situ expendable bathythermograph (XBT) measurements periodically carried out during the survey. We found that the relative change of the two independent measurements are in good agreement within 5% of the typical amplitude of temporal variation.

  58. Detecting horizontal gradient of sound speed in ocean 査読有り

    Motoyuki Kido

    EARTH PLANETS AND SPACE　59　(12)　E33-E36　2007年

    出版者・発行元：SPRINGER HEIDELBERG

    ISSN：1880-5981

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    We propose a new approach to monitor the horizontal gradient of sound speed in ocean for its correction on seafloor positioning using the GPS/acoustic technique. The new method requires five seafloor transponders to solve five parameters: delta x, horizontal position of a transponder array; delta t, a common delay in traveltimes due to the stratified component of sound speed; del(t), the gradient of traveltime delays among the transponders associated with the sound speed gradient. We also numerically evaluate the geometrical strength of the five transponders' layout and observation point to avoid possible trade-off among the parameters.

  59. Seafloor displacement at Kumano-nada caused by the 2004 off Kii Peninsula earthquakes, detected through repeated GPS/Acoustic surveys 査読有り

    Motoyuki Kido, Hiromi Fujimoto, Satoshi Miura, Yukihito Osada, Kentaro Tsuka, Takao Tabei

    EARTH PLANETS AND SPACE　58　(7)　911-915　2006年

    出版者・発行元：TERRA SCIENTIFIC PUBL CO

    DOI： 10.1186/BF03351996 　

    ISSN：1343-8832

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    In 2004, we started monitoring crustal deformation at Kumano-nada in the Nankai trough using the GPS/Acoustic technique. We observed a large southward sealloor displacement of similar to 30 cm associated with the off Kii Peninsula earthquake, which occurred in September 2004, between our two survey campaigns in August and November 2004. The observed seafloor displacement is larger than that predicted from a slip model derived solely from GPS measurements on land. This may indicate the earthquake fault is slightly shallower and extends move to the NW than previously estimated.

  60. 海底地殻変動観測による沈み込み運動の現場観測 招待有り

    藤本博巳, 三浦哲, 日野亮太, 木戸元之, 長田幸仁

    月刊地球　51　(51)　188-192　2005年

    出版者・発行元：海洋出版

    ISSN：0916-9733

  61. 1-D resistivity structures of the oceanic crust around the hydrothermal circulation system in the central Mariana Trough using Magnetometric Resistivity method 査読有り

    N Tada, N Seama, TN Goto, M Kido

    EARTH PLANETS AND SPACE　57　(7)　673-677　2005年

    出版者・発行元：TERRA SCIENTIFIC PUBL CO

    DOI： 10.1186/BF03351846 　

    ISSN：1343-8832

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    We present preliminary results of an electromagnetic survey over a region of hydrothermal circulation in the spreading axis of the central Mariana Trough. The Magnetometric Resistivity (MMR) method is used to determine the electrical resistivity structure of the oceanic crust around the hydrothermal system. 1-D electrical resistivity structure is calculated from the relation between the amplitude of magnetic field and source-receiver separation. The amplitudes of magnetic field variation of ocean bottom magnetometers (OBMs) placed on axis are larger than those of OBMs about 700 m away from the spreading axis, for source-receiver separations larger than 400 m. We estimated two resistivity structure models: one for the axial OBMs, and another for the off-axis OBMs. A region of lower resistivity between depths of 100-300 m is identified in the on-axis model. The hydrothermal source of the Alice Springs Field probably exists beneath the spreading axis, and the size of this source is smaller than 700 m. Lower resistivities at a depth of 50 m are identified in both the on-axis and the off-axis models, suggesting that the porosity in the uppermost oceanic crust is largest at this depth.

  62. Magnetic dipole anomalies as indicators of mantle wedge serpentinization 査読有り

    Y Kido, M Kido, K Fujioka

    GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS　5　(8)　doi:10.1029/2004GC000697　2004年8月

    出版者・発行元：AMER GEOPHYSICAL UNION

    DOI： 10.1029/2004GC000697 　

    ISSN：1525-2027

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    Fine-scale magnetic anomaly data based on high-density airborne surveys have revealed several dipole anomalies along the Chichibu Zone (CZ), which lies parallel to the Nankai Trough and forms a part of the accretionary complex of southwest Japan. A plausible explanation of magnetic sources for the anomalies is a series of fossil serpentine diapirs involved during the accretion process. Serpentine diapirs are known to be developed in several forearc regions as mantle wedge serpentinized material associated with dehydration of the subducting oceanic slab. Surface geological and paleomagnetic evidence also suggests the existence of serpentine bodies in the CZ. We applied a magnetic inversion to each of the dipole anomalies and determined the magnetic bodies in a triaxial ellipsoid approximation. Magnetic bodies are interpreted to lie nearly parallel to the CZ and are inclined southward. Intensities of magnetization are compatible with those expected by measured susceptibilities of samples in the subareal CZ, and their directions are roughly the same as the current geomagnetic field, implying that the induced magnetization is dominant rather than the remanent component.

  63. 局在化アドミッタンスで見るリソスフェア 招待有り

    木戸元之

    月刊地球　25　(7)　530-534　2003年

    出版者・発行元：海洋出版

    ISSN：0387-3498

  64. Continuous wavelet-like filter for a spherical surface and its application to localized admittance function on Mars 査読有り

    M Kido, DA Yuen, AP Vincent

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS　135　(1)　1-16　2003年1月

    出版者・発行元：ELSEVIER SCIENCE BV

    DOI： 10.1016/S0031-9201(02)00176-0 　

    ISSN：0031-9201

    詳細を見る 詳細を閉じる

    We have developed a 2D isotropic continuous wavelet-like transform for a spherical surface. The transform is simply defined as the surface convolution between the original field and a kernel, based on the zeroth-order Bessel function with a spherical correction. This spherical correction violates the geometric similarity for the various scales of the kernels, which becomes more apparent at longer wavelengths. We found numerically that this transform is practically equivalent to a Gaussian bandpass filter in the spherical harmonic domain. We have applied this wavelet-like transform on the recently acquired Martian gravity and topography fields. Using a ratio constructed locally from these two fields, we have constructed a map describing the lateral variations of the localized admittance function on Mars. (C) 2002 Elsevier Science B.V. All rights reserved.

  65. Geophysical applications of multidimensional filtering with wavelets 査読有り

    DA Yuen, AP Vincent, M Kido, L Vecsey

    PURE AND APPLIED GEOPHYSICS　159　(10)　2285-2309　2002年9月

    出版者・発行元：SPRINGER BASEL AG

    DOI： 10.1007/s00024-002-8736-5 　

    ISSN：0033-4553

    詳細を見る 詳細を閉じる

    We present imaging results in geophysics based on using multidimensional Gaussian wavelets as a filter in a 2-D Cartesian domain. Besides decomposing the field into various distinct lengthscales, we have also constructed the 2-D maps describing the spatial distributions of the maximum of the wavelet-transformed 1-2-norm E-max (x,y) and its corresponding local wavenumber k(max) (x,y), where x and y are the Cartesian coordinates. For geoid anomalies, using a wavelet filter extending to 90 degrees, we have discerned the distinct outlines of convergent and divergent tectonic zones and have conducted a quantitative comparison of the short-wavelength gravitational anomalies at those wavelengths between two different geographical locations. We have also compared the wavelet results with a nonlinear bandpass filter in the spectral domain where a Gaussian filter with the logarithm of the degree I acting as the argument has been employed. A wavelet solution, with a length-scale corresponding to 256 degrees, would need a filter with over 400 spherical harmonics centering around l = 157 for an optimal spatial fit. The computational effort with the bandpass filter technique greatly exceeds those associated with wavelets. We have also shown the ability of the wavelets to analyze the vastly different scales present in high Rayleigh number convection and the mixing of passive heterogeneities driven by thermal convection. Wavelets will be a useful tool for rapid analyzing of the large multidimensional fields to be captured in many other geophysical endeavors, such as the upcoming gravity satellite missions and satellite radar interferometry images.

  66. Numerical simulation for the prediction of the plate motions: Effects of lateral viscosity variations in the lithosphere 査読有り

    M Yoshida, S Honda, M Kido, Y Iwase

    EARTH PLANETS AND SPACE　53　(7)　709-721　2001年

    出版者・発行元：TERRA SCIENTIFIC PUBL CO

    DOI： 10.1186/BF03352399 　

    ISSN：1343-8832

    詳細を見る 詳細を閉じる

    A numerical simulation of Newtonian viscous flow without inertia terms in a 3-D spherical shell driven by the negative buoyancy due to the slabs has been conducted to understand the effects of weak plate margins on the plate motions. Density loads are inferred from the seismicity and the reconstruction of the subduction history. The toroidal energy of plate motion comparable to the poloidal energy appears, when gamma (ratio of the viscosity at margins to that of interiors) becomes O(0.01). For the whole mantle density model, all the plates move too fast relative to the Pacific plate. The direction of major plate motions is generally improved by the inclusion of weak plate boundaries. The density loads in the upper mantle appear to explain the overall plate motions, although some of the plate motions may require hidden and/or deeper density anomalies to be consistent with the observations. As gamma decreases, the geoid anomalies associated with the upper mantle slabs change their signs. This reversal affects the long-wavelength components of the geoid anomalies. A considerable part of the horizontal stress field shows a horizontal extension suggesting that another type of density anomalies is necessary to explain the general compressional field of the real Earth.

  67. The role played by a low viscosity zone under a 660 km discontinuity in regional mantle layering 査読有り

    M Kido, DA Yuen

    EARTH AND PLANETARY SCIENCE LETTERS　181　(4)　573-583　2000年9月

    出版者・発行元：ELSEVIER SCIENCE BV

    DOI： 10.1016/S0012-821X(00)00217-X 　

    ISSN：0012-821X

    詳細を見る 詳細を閉じる

    Our previous work from regional geoid inversion over oceans has shown that there exists a low viscosity zone (LVZ) under the 660 km boundary. Nonlinear inversion has been applied for fitting to the intermediate-wavelength oceanic geoid without invoking a priori any impermeable boundary. In this study we have conducted a systematic search of the dependence of the depth of this regional boundary from 660 to 1000 km. We found that the use of this boundary at the depth of the LVZ exerts little influence on the inversion. The LVZ can act regionally as an impermeable boundary, and enhances very fast lateral flow at the uppermost lower mantle. On the other hand, impermeable boundary alone is not caused by a LVZ, as shown also by analysis of the 2D flow patterns, driven by internal density anomalies inferred from tomography. From the intermediate-wavelength geoid, we can not resolve the existence of layering, when the LVZ exists beneath the 660 km boundary. However, a LVZ is needed to fit the geoid. This LVZ can have profound influence on the geodynamical behavior of mantle circulation and the dispersal of geochemical anomalies and the generation of seismic anisotropy. (C) 2000 Elsevier Science B.V. All rights reserved.

  68. Mantle viscosity derived by genetic algorithm using oceanic geoid and seismic tomography for whole-mantle versus blocked-flow situations 査読有り

    M Kido, DA Yuen, O Cadek, T Nakakuki

    PHYSICS OF THE EARTH AND PLANETARY INTERIORS　107　(4)　307-326　1998年5月

    出版者・発行元：ELSEVIER SCIENCE BV

    DOI： 10.1016/S0031-9201(98)00077-6 　

    ISSN：0031-9201

    詳細を見る 詳細を閉じる

    We have applied the genetic algorithm (GA) technique, a nonlinear global optimization method, to determine the radial viscosity structure of the mantle from regional geoidal patterns. From numerical simulations of 2-D mantle convection, we examine the horizontal spectra of the vertical mass flux at 660 km depth and iind that for long wavelengths then are minor differences between partially layered convection induced by the phase transitions and mantle convection without any phase transition. The differences in the spectra of the vertical mass flux become more prominent at shorter wavelengths. This result has led us to study mantle viscosity for the intermediate wavelength geoid from the whole-mantle and blocked-flow situations, in which the appropriate boundary condition is imposed on the radial velocity at 660 km depth. In order to confirm the robustness of this study, two different density models have been used, which were constructed from three tomographic models and appropriate velocity-to-density scaling relations based on recent results from mineral physics. We have analyzed only oceanic geoid spanning between spherical harmonic degree l = 12-25, The correlation of the predicted geoid with the observations over the Atlantic, Indian, and Pacific Oceans have been employed as the fitting function in our GA approach, which has been modified from the common algorithm, In constructing the families of suitable viscosity profiles, we have used 100 parents, which have been iterated for 100 generations, and have been started with 10 different sets of initial parents. Convergence to acceptable viscosity solutions is obtained for all the three oceans and for both the whole-mantle and layered models. In some cases multiple viscosity solutions are found acceptable by using the correlation criteria. The outstanding feature of these models is the nearly ubiquitous presence of two low viscosity zones, one lying under the lithosphere, the other right under the bottom of the spinel to perovskite phase change, The solutions for the whole-mantle model can fit better and are preferred over the solutions with the layered boundary condition, which generally result in unrealistic viscosity profiles. Our results would suggest a more complex mantle viscosity structure, which has not been detected previously from geoid signals with longer wavelengths, and also reveal the potential difficulties in treating the dynamical boundary condition at the 660 km discontinuity. (C) 1998 Elsevier Science B.V. All rights reserved.

  69. New perspectives on mantle dynamics from high-resolution seismic tomographic model P1200 査読有り

    O Cadek, DA Yuen, H Cizkova, M Kido, HW Zhou, D Brunet, P Machetel

    PURE AND APPLIED GEOPHYSICS　151　(2-4)　503-525　1998年3月

    出版者・発行元：BIRKHAUSER VERLAG AG

    DOI： 10.1007/s000240050126 　

    ISSN：0033-4553

    詳細を見る 詳細を閉じる

    Recently a high-resolution tomographic model, the P1200, based on P-wave travel times was developed, which allowed for detailed imaging of the top 1200 km of the mantle. This model was used in diverse ways to study mantle viscosity structure and geodynamical processes. In the spatial domain there are lateral variations in the transition zone, suggesting interaction between the lower-mantle plumes and the region from 600 km to 1000 km. Some examples shown here include the continental region underneath Manchuria, Ukraine and South Africa, where horizontal structures lie above or below the 660 km discontinuity. The blockage of upwelling is observed under central Africa and the interaction between the upwelling and the transition zone under the slow Icelandic region appears to be complex. An expansion of the aspherical seismic velocities has been taken out to spherical harmonics of degree 60. For degrees exceeding around 10, the spectra at various depths decay with a power-law like dependence on the degree, with the logarithmic slopes in the asymptotic portion of the spectra containing values between 2 and 2.6. These spectral results may suggest the time-dependent nature of mantle convection. Details of the viscosity structure in the top 1200 km of the mantle have been inferred both from global and regional geoid data and from the high-resolution tomographic model. We have considered only the intermediate degrees (l = 12-25) in the nonlinear inversion with a genetic algorithm approach. Several families of acceptable viscosity profiles are found for both oceanic and global data. The families of solutions for the two data sets have different characteristics. Most of the solutions associated with the global geoid data show the presence of asthenosphere below the lithosphere. In other families a low viscosity zone between 400 and 600 km depth is found to lie atop a viscosity jump. Other families evidence a viscosity decrease across the 660 km discontinuity. Solutions from oceanic geoid show basically two low viscosity zones: one lying right below the lithosphere; the other right under 660-km depth. All of these results bespeak clearly the plausible existence of strong Vertical Viscosity stratification in the top 1000 km of the mantle. The presence of the second asthenosphere may have important dynamical ramifications on issues pertaining to layered mantle convection. Numerical modelling of mantle convection with two phase transitions and a realistic temperature-and pressure-dependent viscosity demonstrates that a low viscosity region under the endothermic phase transition can indeed be generated self-consistently in time-dependent situations involving a partially layered configuration in an axisymmetric spherical-shell model.

  70. ジオイドからわかるマントルレオロジー 招待有り

    木戸元之

    月刊地球　20　265-270　1998年

  71. Synthetic tests of geoid-viscosity inversion: A layered viscosity case 査読有り

    M Kido, S Honda

    EARTH PLANETS AND SPACE　50　(11-12)　1055-1065　1998年

    出版者・発行元：TERRA SCIENTIFIC PUBL CO

    DOI： 10.1186/BF03352200 　

    ISSN：1343-8832

    詳細を見る 詳細を閉じる

    We revisited the resolving power of viscosity inversion in terms of geoid misfit in a 2-D Cartesian geometry under the assumption that the mantle viscosity is laterally stratified. Firstly, we considered a simple case of two viscosity layers only, which is described by two parameters of the amount and the depth of the viscosity jump. The uniqueness of the inversion was examined by evaluating misfits between the: reference geoid for a reference viscosity and that for a viscosity described by the changing two parameters. The misfits are mapped into 2-D model space as a function of the two parameters. Three types of density distribution are tested; they are vertically constant (1), taken from a tomographic model (2), and the same but includes artificial noise (3). We found that, at least for this simple case, the viscosity solution keeps unique in the entire 2-D model space using whole degree band (1-8) of geoid. This holds even if the artificial noise is rather large (70%), though the solution is slightly different from the reference viscosity. However, we also observed non-uniqueness, such as trade-off between the two parameters, when individual degree components of geoid are concerned. In the next, we employed a more realistic viscosity structure, having seven iso-viscous layers. It is no longer possible to describe 6-D model space easily. Therefore we tried to reconstruct a reference viscosity from the reference geoid using genetic algorithm search. According to this analysis, nearly the same solution with the reference viscosity can be reconstructed, while solutions apart from the reference viscosity with increase of noise in the density distribution.

  72. Inferences of viscosity from the oceanic geoid: Indication of a low viscosity zone below the 660-km discontinuity 査読有り

    M Kido, O Cadek

    EARTH AND PLANETARY SCIENCE LETTERS　151　(3-4)　125-137　1997年10月

    出版者・発行元：ELSEVIER SCIENCE BV

    DOI： 10.1016/S0012-821X(97)81843-2 　

    ISSN：0012-821X

    詳細を見る 詳細を閉じる

    We have attempted to infer details of the viscosity structure in the top 1000 km of the mantle from the geoid and tomographic structure beneath the oceans. In order to eliminate the gravity signal from problematic masses located below the subduction zones and the continents, we have considered only the intermediate degrees of the oceanic geoid (l = 12-25). A genetic algorithm has been used to determine the family of viscosity models which give the best correlation with the observed geoid. Our inversion clearly identifies the asthenosphere just below the lithosphere and also confirms the viscosity increase in the lower mantle predicted by previous inferences, but suggests that the main viscosity jump occurs at a depth of about 1000 km and not at the usually stated 660-km boundary. Somewhere in the depth range of 400-1000 km, a low viscosity zone may exist where the viscosity decreases to a value comparable with the asthenosphere. Existence of such a low viscosity zone is supported by recent analysis of deep mantle anisotropy which favours a flow pattern with a strong horizontal component in the top part of the lower mantle. Unfortunately, the resolution of the inversion as well as the quality of recent seismic tomographic models are not sufficient to localize the depth and to come up with a higher accuracy for the viscosity of this low viscosity channel. (C) 1997 Elsevier Science B.V.

  73. MORPHOLOGICAL-STUDIES OF THE AYU TROUGH, PHILIPPINE-SEA CAROLINE PLATE BOUNDARY 査読有り

    T FUJIWARA, K TAMAKI, H FUJIMOTO, T ISHII, N SEAMA, H TOH, K KOIZUMI, C IGARASHI, J SEGAWA, K KOBAYASHI, M KIDO, T SENO, H KINOSHITA

    GEOPHYSICAL RESEARCH LETTERS　22　(2)　109-112　1995年1月

    出版者・発行元：AMER GEOPHYSICAL UNION

    DOI： 10.1029/94GL02719 　

    ISSN：0094-8276

    詳細を見る 詳細を閉じる

    The Ayu Trough lies on the southern boundary between the Philippine Sea Plate and Caroline Plate. Although this trough may be the best place to study the evolution and kinematics of the Philippine Sea Plate, the origin and evolution of this trough are poorly understood. Our geophysical and morphological surveys in the northern part of the Ayu Trough revealed that the trough shares morphological similarities with slow-spreading mid-ocean ridges. The seafloor ages and an average spreading rate of the trough were inferred from the average length of the ridge segments, distribution of sediment thickness, and basement subsidence. Based on the seismic section at 3 degrees 30'N, the opening of the trough started about 25 Ma with an average half-spreading rate 4.1 mm/yr. This spreading rate is much slower than some previous estimates. The present magma production rate and activity of the trough is estimated to be even lower than the 25 m.y. average. The seafloor depth of the trough axis and relief of the axial valley are approximately twice as deep as that of active mid-ocean ridges. The trough axis valley is covered with sediment in contrast with the axial valleys of active mid-ocean ridges. Sedimentation at the trough axis shows that the spreading rate has been quite slow for the last 2.5 Ma.

  74. DYNAMIC TOPOGRAPHY COMPARED WITH RESIDUAL DEPTH ANOMALIES IN OCEANS AND IMPLICATIONS FOR AGE-DEPTH CURVES 査読有り

    M KIDO, T SENO

    GEOPHYSICAL RESEARCH LETTERS　21　(8)　717-720　1994年4月

    出版者・発行元：AMER GEOPHYSICAL UNION

    DOI： 10.1029/94GL00305 　

    ISSN：0094-8276

    詳細を見る 詳細を閉じる

    Ocean depth is affected by dynamic topography caused by mantle flow. Regional bathymetric deviations from the cooling plate age-depth curve, called residual depth anomalies, can therefore be used as indicators of dynamic topography in oceans. In this work, we first evaluated the oceanic residual depth anomalies. We then compute the dynamic topography for the flow induced by density perturbations converted from seismic tomography models by assuming deltarho is-proportional-to deltav. We found that the predicted dynamic topography correlates with the depth anomalies when the density perturbations in the shallow part of the upper mantle were inferred from slab densities, not from tomographic models. We estimated a new age-depth curve based on depths corrected for dynamic topography. This corrected age-depth curve shows that the corrected depths for old seafloor (70 approximately 110 Ma) are a few hundred meters deeper than those uncorrected.

  75. アユトラフとはなにか？ —白鳳丸KH92-1 航海地球物理調査の成果—

    富士原敏也, 木戸元之, 玉木賢策, 藤本博巳, 瀬野徹三, 木下肇, 藤浩明, 石井輝秋, 五十嵐千秋, 小林和男, 瀬川爾朗

    月刊海洋　24　(9)　532-538　1994年

  76. 海洋プレートの進化に関する研究の動向 査読有り

    木戸元之, 木下肇

    地震　47　468-488　1994年

    DOI： 10.4294/zisin1948.47.4_469 　

  77. 地震波トモグラフィーから予想される現在のマントル対流パターンについて 査読有り

    木戸元之

    地震　47　411-421　1994年

    DOI： 10.4294/zisin1948.47.4_411 　

  78. P42 アユトラフについて : 白鳳丸 KH92-1 航海地球物理地質・調査の成果

    富士原 敏也, 石井 輝秋, 玉木 賢策, 藤本 博巳, 藤浩 明, 小泉 金一郎, 五十嵐 千秋, 小林 和男, 瀬川 爾朗, 木戸 元之, 瀬野 徹三, 木下 肇, 竹村 治, 横瀬 久芳

    日本火山学会講演予稿集　1992　176-176　1992年

    出版者・発行元：特定非営利活動法人 日本火山学会

    DOI： 10.18940/vsj.1992.2.0_176 　

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MISC 9

  1. 新しいプレート境界モデルに向けた海底地震地殻変動モニタリング観測研究と技術開発

    篠原雅尚, 塩原肇, 望月公廣, 山田知朗, 一瀬建日, 村井芳夫, 日野亮太, 藤本博己, 木戸元之, 伊藤喜宏, 佐藤利典, 清水洋, 八木原寛, 酒井慎一, 小原一成, 平田直

    日本地震学会秋季大会講演予稿集　2012　34　2012年10月1日

  2. A long-term seafloor experiment using an acoustic ranging system: Precise horizontal distance measurements for detection of seafloor crustal deformation

    Osada, Y., Kido, M., Fujimoto, H.

    Ocean Engineering　51　2012年

    DOI： 10.1016/j.oceaneng.2012.05.006 　

  3. GPS/Acoustic measurement with higher accuracy by means of stationary survey

    Kido, M, H. Fujimoto, Y. Osada

    Proc. 22nd Ocean Engineering Symposium, Tokyo, March 17-18, 2011　OES22　039　2011年

  4. P-53 日本海溝におけるゆっくり地震検出のための海底地震・測地および湧水観測 : YK08-06航海の概要と成果(11.海洋地質,ポスター発表,一般講演)

    伊藤 喜宏, 藤本 博己, 日野 亮太, 木戸 元之, 長田 幸仁, 鈴木 秀市, 山本 揚二朗, 東 龍介, 対馬 弘晃, 鈴木 健介, 辻 健, 中山 典子, 芦 寿一郎, 蒲生 俊敬

    日本地質学会学術大会講演要旨　115　198-198　2008年9月15日

    出版者・発行元：日本地質学会

  5. 2004年紀伊半島南東沖地震震源域周辺の海底観察と地殻変動観測用海底局の姿勢安定性の検証

    藤本博己, 木戸元之, 長田幸仁, 田所敬一, 奥田隆, 松本良浩, 栗原梢

    海洋研究開発機構航海概要報告(CD-ROM)　2006　2008年

  6. Detecting horizontal gradient of sound speed in ocean

    Kido Motoyuki

    Earth, planets and space　59　(12)　e33-e36　2007年12月1日

    出版者・発行元：Terra Scientific Pub. Co.

    ISSN：1343-8832

  7. 海底地殻変動観測用海底局の安定性:2004年紀伊半島南東沖地震後の潜航調査

    藤本博己, 田所敬一, 奥田隆, 松本良浩, 木戸元之, 長田幸仁, 栗原梢

    しんかいシンポジウム予稿集　23rd　2007年

  8. Toward semi-real-time GPS/A seafloor positioning with a moored Buoy

    Fujimoto, H, M. Kido, Y. Osada, Y. Kaneda

    Proc. Symposium on Underwater Technology 2007 and International Workshop on Scientific Use of Submarine Cables and Related Technologies 2007, Tokyo, April 2007　IEEE Catalog Number: 07EX1770C　211-216　2007年

    DOI： 10.1109/UT.2007.370787 　

  9. 2004年紀伊半島南東沖地震後における海底地殻変動観測用海底局の安定性に関する潜航調査

    藤本博己, 田所敬一, 奥田隆, 松本良浩, 木戸元之, 長田幸仁, 栗原梢

    日本測地学会講演会要旨　106th　2006年

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講演・口頭発表等 16

  1. 海底地殻変動観測手法高度化における問題点とその解決のための提案

    木戸元之, 長田幸仁, 藤本博己

    日本地球惑星科学連合2010年　2011年5月25日

  2. Temporal variation of oceanic sound speed structure affecting seafloor geodesy 国際会議

    Kido, M, H. Fujimoto, Y. Osada

    2010 AGU Fall Meeting　2010年12月13日

  3. 海底地殻変動観測のこれまでの成果と今後の展望について

    木戸元之, 長田幸仁, 藤本博己

    日本地震学会2010年秋季大会　2010年10月28日

  4. 海底地殻変動観測システムの高度化

    木戸元之

    「地震及び火山噴火予知のための観測研究計画」成果報告シンポジウム　2010年3月3日

  5. GPS/音響方式による海底地殻変動観測の精度改善への取り組み

    日本地震学会2009年秋季大会　2009年10月

  6. Seafloor geodesy using the GPS/acoustic technique: towards next generation approach

    第21回海洋工学シンポジウム　2009年8月

  7. Technical development of analysis in seafloor geodetic measurement

    木戸元之, 長田幸仁, 藤本博

    日本地球惑星科学連合大会　2009年5月

  8. 分岐断層活動検出へ向けた海底間音響測距装置の安定した潜航設置―NT08-19航海（熊野灘外縁部）の概要―

    木戸元之, 長田幸仁, 岩崎望, 兵藤一星, 荒井崇臣, 山根広, 岩本久則

    Blue Earth Symposium　2009年3月

  9. Development of a new tubular buoy for seafloor geodetic observation with cabled system 国際会議

    Kido, M, Y. Osada, H. Fujimoto, Y. Kaneda

    AGU 2008 Fall meeting　2008年12月15日

  10. Tracking buoy motion/attitude using incomplete rate-gyro data in the GPS/acoustic measurement 国際会議

    Kido, M, H. Fujimoto, Y. Osada

    ASC-SSJ　2008年11月24日

  11. 海中音速傾斜推定における誤差伝播について

    木戸元之, 長田幸仁, 藤本博己

    日本測地学会第110回講演会　2008年10月22日

  12. 係留ブイ方式に向けた海底地殻変動観測システムの開発

    木戸元之, 長田幸仁, 藤本博己, 金田義行

    日本地球惑星科学連合2008年大会　2008年5月25日

  13. Monitoring the Lateral Gradient of Sound Speed in Ocean Toward Fast GPS/Acoustic Seafloor Positioning for the Cabled System 国際会議

    AGU Fall Meeting　2007年12月10日

  14. 海底地殻変動観測における傾斜を含む音速場の推定と観測精度について

    日本測地学会 第108回講演会　2007年11月8日

  15. GPS/音響海底測地観測における海中音速の傾きについて

    木戸元之, 長田幸仁, 藤本博己

    日本地震学会秋季大会　2007年10月24日

  16. A feasibility study of monitoring of the horizontal gradient of sound speed in ocean 国際会議

    EASTEC symposium 2007　2007年9月19日

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共同研究・競争的資金等の研究課題 8

  1. 津波情報の即時伝達のための水中音響伝送手法の開発

    高橋 成実, 木戸 元之, 今井 健太郎, 越智 寛, 石原 靖久, 太田 雄策, 福田 達也, 近貞 直孝

    2020年4月1日 ～ 2023年3月31日

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    2011年の東日本大震災では、高さ40mを超える津波が襲来し、甚大な被害が発生した。これを受け、日本海溝沿いには日本海溝海底地震津波観測網が敷設され、海底での津波観測と海域での水圧値を用いた津波予測技術が進展し（Tsushima et al., 2012; Takahashi et al., 2018）、いくつかのシステムは気象庁や自治体に実装された。しかし、海底観測網の整備と運用にはコストや人的負担が大きいため、全海域に敷設するのは難しい。遠地地震の監視を目的として、DARTブイシステム（https://nctr.pmel.noaa.gov/Dart/）が太平洋沿岸には設置、運用されているが、これも日本列島南方に流れる黒潮下では、その強潮流により設置することができず、全ての海域に設置できるものではない。これを解決するために、海底で観測した水圧値を音響信号に変換し、複数の中継器を経由して海面に伝送、衛星を通じて陸上にデータを伝送するシステムを検討している。 これを実現するために必要な技術は、海中部のノイズや海面や海底からの反射ノイズに強いこと、消費電力が抑えられて長期的な利用が可能であること、観測データの精度が確保できることである。これを検討するために、一定の数値を音響信号に変換して伝送する音響通信試験を6日間にわたり田沢湖で実施した。通信試験では、湖底に送信機を設置し、２つの一定値を使用して、音響データを直接湖面の受波機に伝送するケースと、中継器でデータを中継してから受波機に伝送するケースの2つの経路で伝送されたデータを比較し、音響伝送の安定性評価を行った。

  2. 近接設置の海底局による精密GPS/Differential-Acoustic観測

    木戸 元之

    提供機関：Japan Society for the Promotion of Science

    制度名：Grants-in-Aid for Scientific Research

    研究種目：Grant-in-Aid for Challenging Research (Exploratory)

    研究機関：Tohoku University

    2017年6月30日 ～ 2019年3月31日

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    海底での局所変動が予想される場所で、海底間の測距が困難な地形に対し、海面からの測距で変動を計測する手法を考案し、実観測を通してその実用性を検証した。日本海溝沿いの逆断層地形での観測で、手法の精度的な妥当性が確認され、同時に観測期間中の変動が無かったことがわかった。一方、紀伊半島沖に設置した機器による詳細な温度計測により、海域によっては本手法を用いても必要な精度が得られない場合があることも判明した。

  3. 海底地殻変動と海水温変動の高精度検出に向けた統合解析：高密度海域観測網の新活用

    有吉 慶介, 五十嵐 俊博, 木戸 元之, 飯沼 卓史, 永野 憲, 長谷川 拓也, 松本 浩幸, 内田 直希, 山下 裕亮, 中田 令子

    提供機関：Japan Society for the Promotion of Science

    制度名：Grants-in-Aid for Scientific Research

    研究種目：Grant-in-Aid for Scientific Research (B)

    研究機関：Japan Agency for Marine-Earth Science and Technology

    2015年4月1日 ～ 2019年3月31日

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    本研究では、南海トラフでは日向灘での海水温・塩分深度分布の観測を独自に行い、海洋変動成分の定量評価を行った。その結果、黒潮大蛇行の形成に伴う海面高度の上昇に約1ヵ月遅れて海底圧力が増加することが分かった。そのような傾圧変化のモデル化として、海底地形によって蛇行が安定化されたという観点から説明した。 釧路沖では、遠洋側と陸側の観測点間で、海面高度変化に対する応答が2007年～2008年の間で異なっていることに着目し、この期間中について海上保安庁の定線観測(A-line)による水温・塩分の鉛直プロファイルを調べたところ、中規模渦が生じていたことを見出した。

  4. 沈み込み帯浅部のスロースリップはトラフ軸まで到達するか？

    伊藤 喜宏, 木戸 元之, 芝崎 文一郎, 日野 亮太, 日野 亮太, 小原 一成, 篠原 雅尚, 望月 公廣

    提供機関：Japan Society for the Promotion of Science

    制度名：Grants-in-Aid for Scientific Research

    研究種目：Grant-in-Aid for Scientific Research (A)

    研究機関：Kyoto University

    2014年4月1日 ～ 2019年3月31日

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    ニュージーランドの北島の東方沖に位置するヒクランギ沈み込み帯の北部で実施した海底圧力観測記録に基づき、得に2014年のスロースリップがトラフ軸近傍まで到達していることを明らかにした。加えて、ヒクランギ沈み込み帯で発生するスロースリップの動的トリガリングのモデル化も行なった。特に2016年に発生したカイコウラ地震により生じた地震波動による動的応力擾乱を考慮することで、浅部のスロースリップの発生をよく再現できることを示した。

  5. 海中音速不均質推定による海底地殻変動観測精度の向上

    木戸 元之

    提供機関：Japan Society for the Promotion of Science

    制度名：Grants-in-Aid for Scientific Research

    研究種目：Grant-in-Aid for Challenging Exploratory Research

    研究機関：Tohoku University

    2015年4月1日 ～ 2017年3月31日

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    海底地殻変動観測の精度向上には海中音速場の擾乱の推定が欠かせない。的確なモデルを構築するために、投げ入れ式の温度センサーであるXBTを用いて海中の温度プロファイルを連続的に集中観測した。それらの時系列解析から短周期擾乱の原因を海中の重力波であることを突き止めた。重力波をモデルとして音速の補正方法を確立することで、海底地殻変動観測の水平変位の検出精度が向上すると当時に、上下変動の推定も可能となった。

  6. 海底地殻変動連続観測のための高精度姿勢把握システムの構築

    太田 雄策, 木戸 元之

    提供機関：Japan Society for the Promotion of Science

    制度名：Grants-in-Aid for Scientific Research

    研究種目：Grant-in-Aid for Challenging Exploratory Research

    研究機関：Tohoku University

    2015年4月1日 ～ 2017年3月31日

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    海域における地殻変動観測の高度化のためには，低消費電力で海上プラットホームの位置・姿勢把握の実現が重要である．本研究では，単一GNSSアンテナと慣性航法装置を用いた，より消費電力の低いリアルタイム洋上部姿勢把握システムの開発を実施した．開発では(1)超低消費電力GNSS連続観測システムの開発と(2) 単一アンテナと慣性航法装置による洋上部プラットホームの姿勢把握アルゴリズムの開発を行った．その結果，(1)については3W以下の消費電力で必要な機能を提供できるシステムの開発に成功した．(2)については方位角で0.5度，ピッチ・ロール角で0.4度の精度で姿勢を把握できるアルゴリズムの開発に成功した．

  7. 海底測地・地震観測に基づくマルチスケールゆっくり地震の検出

    藤本 博己, 伊藤 喜宏, 木戸 元之, 日野 亮太

    提供機関：Japan Society for the Promotion of Science

    制度名：Grants-in-Aid for Scientific Research

    研究種目：Grant-in-Aid for Scientific Research (A)

    研究機関：Tohoku University

    2008年 ～ 2012年

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    東北日本沈み込み帯においてスロー地震観測のための海底測地・地震観測網を構築し、スロースリップの検出に先行した。スロースリップは、2008年と2011年の2回観測された。いずれのスロースリップも中規模ないしは大規模なプレート境界型地震に先行して観測された。特に2011年のスロースリップは、2011年3月11日の東北地方太平洋沖地震の震源域内で3月9日の最大前震(M7.3)に先行して発生していた。これらの観測は、スロースリップがプレート境界型地震の発生過程における応力蓄積過程で重要な役割を果たすことを示唆するものである。

  8. 海底地殻変動観測 競争的資金

    制度名：Funded Research

    2003年4月 ～

︎全件表示 ︎最初の5件までを表示

その他 1

  1. 海底地殻変動観測技術の高度化

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    今後予想される海溝型巨大地震の想定震源域は海域にあり、その周辺における地殻変動観測により、プレート境界の固着状態の空間分布を把握し、その時間変動をモニターすることが今後の重要な課題である。そのためには、想定震源域とその周辺において広域かつ高密度で精密な地殻変動連続観測が必要である。しかし現状のGPS音響結合方式の海底地殻変動観測は、条件により測位精度1～5cm程度の孤立した点における観測であり、観測頻度は多くても年に2～3回の繰り返し観測である。しかも観測の結果が得られるのは1か月程度経過したのちである等の問題点が存在する。本研究は、その海底地殻変動の高度化を実現するために必要な観測システム及び解析手法を開発することを目的とするものである。当初平成26年度までの5年計画の予定であったが、平成23年度補正予算による研究の強化により、本研究は、平成25年度までに1回の測位精度を1cm程度まで向上させ、海溝型巨大地震の想定震源域内及びその周辺や東北地方太平洋沖地震の余効変動域における広域・高密度観測を進め、速報値を観測終了後半日程度で求め、セミリアルタイム化を実現することを目標とする。重要な観測点においては係留ブイによる連続観測を実現し、日座標値の時系列データを得られるようにする。今後の観測形態としては、船を用いた移動観測と自航式ブイを用いた同時観測、さらに係留ブイを用いた連続観測が必要となることを踏まえ、①移動観測における高精度かつ高効率な海底地殻変動観測・解析技術の開発、②セミリアルタイム海底地殻変動連続観測に向けたシステム開発、及び集中観測による東北地方太平洋沖地震の余効変動の検出を目標として本業務を実施する。