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研究者データベース

詳細
古屋　正人(フルヤ　マサト)
理学研究院　地球惑星科学部門　地球惑星ダイナミクス分野
教授
researchmap個人ページ
Last Updated :2024/05/09

基本情報

所属

  • 理学研究院　地球惑星科学部門　地球惑星ダイナミクス分野

職名

  • 教授

ホームページURL

科研費研究者番号

  • 60313045

ORCID ID

Researcher ID

  • E-1296-2011

J-Global ID

研究キーワード

  • 極端気象   重力   火山   地震   InSAR   永久凍土   電離層   氷河   地球回転   地殻変動   合成開口レーダー   宇宙測地学   

研究分野

  • 自然科学一般 / 宇宙惑星科学
  • 環境・農学 / 環境動態解析
  • 自然科学一般 / 大気水圏科学
  • 社会基盤（土木・建築・防災） / 防災工学
  • 自然科学一般 / 固体地球科学

担当教育組織

職歴

  • 2012年01月 - 現在 北海道大学 大学院 理学研究院 地球惑星科学部門
  • 2007年10月 - 2011年12月 北海道大学 大学院 理学研究院 地球惑星科学部門
  • 1999年04月 - 2007年09月 東京大学 地震研究所
  • 2003年08月 - 2005年07月 コロラド大学ボルダー校 物理学科
  • 1997年04月 - 1999年03月 郵政省通信総合研究所

学歴

  •         - 1997年   東京大学   理学系研究科   地球惑星物理学専攻
  •         - 1997年   東京大学
  •         - 1992年   東京大学   理学部
  •         - 1992年   東京大学

所属学協会

  • 日本雪氷学会   日本気象学会   日本地震学会   日本火山学会   日本測地学会   Japanese Geoscience Union   American Geophysical Union   The meteorological society of Japan   The seismological society of Japan   The volcanological society of Japan   The geodetic society of Japan   

研究活動情報

論文

  • Ryuji Yamaguchi, Masato Furuya
    Earth, Planets and Space 76 1 2024年01月02日 [査読有り]
     
    Abstract Recent polar motion data do not show a 6-year beat and indicate the absence of the Chandler wobble (CW), whereas we could observe the 6-year beat even in the 1920-40 s when the CW amplitude was known to be smallest. As a free mode, the CW needs excitation one or more sources that were debated decades ago but are now attributed to the atmosphere, ocean, and possibly land water. Here, we show that the anomaly started in 2015, after which two independent estimates of the atmospheric CW excitation became persistently smaller than before. However, the estimates of the oceanic and land–water contributions are too large, suggesting improved estimates are needed. Taking advantage of the recent CW anomaly, we show that the quality factor of CW is not as high as 100 as previously preferred. Although the CW excitation processes have been assumed random, a termination of near-resonant processes would rather be consistent with the present findings. Graphical Abstract
  • Yasuo Ogawa, Nozomu Nishitani, Masato Furuya, Valerio Acocella, Hauke Hussmann
    Earth, Planets and Space 75 1 2023年12月
  • K. Yanagiya, M. Furuya, P. Danilov, G. Iwahana
    Journal of Geophysical Research: Earth Surface 128 2 2023年02月12日 [査読有り]
  • Masato Furuya, Fumiko Matsumoto
    Geophysical Research Letters 49 1 2021年12月29日 [査読有り]
  • Yosuke Aoki, Masato Furuya, Francesco De Zan, Marie Pierre Doin, Michael Eineder, Masato Ohki, Tim J. Wright
    Earth, Planets and Space 73 1 2021年12月
  • Naufal Setiawan, Masato Furuya
    Earth, Planets and Space 73 1 2021年07月 [査読有り][通常論文]
     
    AbstractThe split-spectrum method (SSM) can largely isolate and correct for the ionospheric contribution in the L-band interferometric synthetic aperture radar (InSAR). The standard SSM is performed on the assumption of only the first-order ionospheric dispersive effect, which is proportional to the total electron content (TEC). It is also known that during extreme atmospheric events, either originated from the ionosphere or in the troposphere, other dispersive effects do exist and potentially provide new insights into the dynamics of the atmosphere, but there have been few detection reports of such signals by InSAR. We apply L-band InSAR into heavy rain cases and examine the applicability and limitation of the standard SSM. Since no events such as earthquakes to cause surface deformation took place, the non-dispersive component is apparently attributable to the large amount of water vapor associated with heavy rain, whereas there are spotty anomalies in the dispersive component that are closely correlated with the heavy rain area. The ionosonde and Global Navigation Satellite System (GNSS) rate of total electron content index (ROTI) map both show little anomalies during the heavy rain, which suggests few ionospheric disturbances. Therefore, we interpret that the spotty anomalies in the dispersive component of the standard SSM during heavy rain are originated in the troposphere. While we can consider two physical mechanisms, one is runaway electron avalanche and the other is the dispersive effect due to rain, comparison with the observations from the ground-based lightning detection network and rain gauge data, we conclude that the rain dispersive effect is spatiotemporally favorable. We further propose a formulation to examine if another dispersive phase than the first-order TEC effect is present and apply it to the heavy rain cases as well as two extreme ionospheric sporadic-E events. Our formulation successfully isolates the presence of another dispersive phase during heavy rain that is in positive correlation with the local rain rate. In comparison with other dispersive phases during Sporadic-E episodes, the dispersive heavy rain phases seem to have the same order of magnitude with the ionospheric higher order effects.
  • Shin Sugiyama, Naoya Kanna, Daiki Sakakibara, Takuto Ando, Izumi Asaji, Ken Kondo, Yefan Wang, Yoshiki Fujishi, Shungo Fukumoto, Evgeniy Podolskiy, Yasushi Fukamachi, Minori Takahashi, Sumito Matoba, Yoshinori Iizuka, Ralf Greve, Masato Furuya, Kazutaka Tateyama, Tatsuya Watanabe, Shintaro Yamasaki, Atsushi Yamaguchi, Bungo Nishizawa, Kohei Matsuno, Daiki Nomura, Yuta Sakuragi, Yoshimasa Matsumura, Yoshihiko Ohashi, Teruo Aoki, Masashi Niwano, Naotaka Hayashi, Masahiro Minowa, Guillaume Jouvet, Eef van Dongen, Andreas Bauder, Martin Funk, Anders Anker Bjørk, Toku Oshima
    Polar Science 27 100632 - 100632 2021年03月 [査読有り][通常論文]
     
    Environments along the coast of Greenland are rapidly changing under the influence of a warming climate in the Arctic. To better understand the changes in the coastal environments, we performed researches in the Qaanaaq region in northwestern Greenland as a part of the ArCS (Arctic Challenge for Sustainability) Project. Mass loss of ice caps and marine-terminating outlet glaciers were quantified by field and satellite observations. Measurements and sampling in fjords revealed the important role of glacial meltwater discharge in marine ecosystems. Flooding of a glacial stream in Qaanaaq and landslides in a nearby settlement were investigated to identify the drivers of the incidents. Our study observed rapid changes in the coastal environments, and their critical impact on the society in Qaanaaq. We organized workshops with the residents to absorb local and indigenous knowledge, as well as to share the results and data obtained in the project. Continuous effort towards obtaining long-term observations requiring involvement of local communities is crucial to contribute to a sustainable future in Greenland.
  • Shohei Narita, Taku Ozawa, Yosuke Aoki, Masanobu Shimada, Masato Furuya, Youichiro Takada, Makoto Murakami
    Earth, Planets and Space 72 1 2020年10月 [査読有り][通常論文]
     
    Abstract We present detailed maps of local-scale 3D deformation preceding the 2018 phreatic eruption at Iwo-yama volcano (south of Kyushu Island, Japan), using a combination of airborne and spaceborne Interferometric Synthetic Aperture Radar (InSAR) data. The 3D and 2.5D deformation maps obtained at different periods allow us to successfully track their spatiotemporal evolution and to infer the transition of subsurface conditions responsible for the precursory deformation observed from 2014 to 2018. From 2014 to 2016, ground inflation depicted an axisymmetric pattern with the maximum displacement at the center of the deformed area. However, from 2016 to 2018, an inflation peak moved to the southern edge of the area deformed during 2014–2016 and became more localized, which was close to the newly generated vents in the 2018 eruption. Modeling of the inflations suggests that pressurization within a crack at a depth of 150 m beneath the Iwo-yama geothermal area caused the 2014–2016 deformation and had continued until the 2018 eruption. Modeling results highlight the persistence of the local ground inflation pattern just above the southern edge of the crack, which suggests the presence of a shallower inflation source contributing to the local inflation. Consequently, we interpret the sequence of these deformations as follows: from 2014, deeper-rooted fluid started to inject into a fluid-saturated crack at 150-m depth, which caused the 2014–2016 deformation. Then, after 2016, the crack inflation continued because of the continuous fluid injection and formed another pressurized part directly above the southern tip of the crack. Additionally, the results of the time-series analysis of the satellite InSAR data revealed that the local inflation started around April 2017 for which thermal activity including a mud emission became pronounced around the location of the local inflation. As a result of an episodic increase in supply rate of magmatic fluids from a deep magma reservoir from early 2018, a phreatic eruption finally occurred in the vicinity of the most deformed point, providing a clue for predicting future eruption sites, as was also observed in the Hakone 2015 eruption.
  • Yuji Himematsu, Masato Furuya
    Earth and Space Science 7 10 2020年10月 [査読有り][通常論文]
  • Yuji Himematsu, Masato Furuya
    Tectonophysics 791 228571 - 228571 2020年09月 [査読有り][通常論文]
  • Kazuki Yanagiya, Masato Furuya
    Journal of Geophysical Research: Earth Surface 2020年06月09日 [査読有り][通常論文]
  • 姫松裕志, シグムンドソン フラインスタイン, 古屋正人
    Journal of Geophysical Research, Solid Earth 124 9 9940 - 9955 2019年09月 [査読有り][通常論文]
     
    Bárðarbunga is an active volcano beneath the Vatnajökull icecap in Iceland, where a subglacial dike intrusion occurred in 2014. This area has been studied with interferometric synthetic aperture radar, an important geodetic method that measures crustal deformation; however, ice/snow cover on volcanoes impedes the mapping of crustal deformation because of decorrelation problems. Previous geodetic observations have reported deformation signals at ice‐free regions of a major dike formed in 2014 in the Bárðarbunga volcanic system, but direct observations of the subglacial crustal deformation associated with the dike intrusion have been limited. We applied a pixel tracking approach to various satellite synthetic aperture radar (SAR) data over the northern part of the Vatnajokull icecap and the Holuhraun plain. The pixel tracking data revealed not only crustal deformation fields in the ice‐free region of the magma intrusion, which covers only about 20% of the entire length of dike, but also icecap surface movements over the subglacial part of the dike in the ablation area of the Vatnajökull icecap. Signals above the icecap, suggesting subsidence due to subglacial graben formation, are consistent with the dike propagation path inferred from seismicity during the episode. By subtracting the scaled pre‐diking signals from the co‐diking signals, we corrected for the steady‐state icecap flow signals to derive the subglacial crustal deformations. We showed that the inferred subglacial crustal deformation signals can significantly contribute to the improvement of dike opening/faulting distributions. Applying the pixel tracking to satellite images will enable mapping subglacial crustal deformation in the case of subglacial volcanic activity.
  • Muhammad Usman, Masato Furuya
    Journal of Glaciology 64 245 465 - 476 2018年06月01日 [査読有り][通常論文]
     
    Unlike in most other regions, Karakoram glaciers are either stable or advancing, a phenomenon known as the Karakoram anomaly. Despite studies of glacier surges and the derivation of surface velocity maps, the spatiotemporal variability of glacier dynamics still remains poorly understood, particularly in the Eastern Karakoram Range. We use Advanced Land Observing Satellite/the Phased Array type L-band Synthetic Aperture Radar (ALOS/PALSAR)-1/2 data from 2007 to 2011 and 2014 to 2015 to examine detailed surface velocity patterns of the Siachen, Baltoro, Kundos, Singkhu and Gasherbrum Glaciers. The first three glaciers show considerable velocity variability (20-350 m a-1), with clear seasonal patterns. Although all glaciers, except for Baltoro, flow slowest in 2015, the velocity structures are individual and vary in space and time. In Gasherbrum Glacier, peak surge-phase velocities are seasonally modulated, with maxima in summers 2006 and 2007, suggesting surface melt plays an important role in maintaining the active phase. Given the relatively close proximity of these glaciers, we assume that surface melt timing and rates are comparable. We therefore argue that the observed spatiotemporal and interannual velocity patterns are determined by local and internal mechanisms, including englacial and subglacial hydrology, thermal processes and tributary configuration of each individual glacier.
  • Iio, Kento, Furuya, Masato
    Progress in Earth and Planetary Science 5 61  2018年 [査読有り][通常論文]
  • Masato Furuya, Takato Suzuki, Jun Maeda, Kosuke Heki
    Earth, Planets and Space 69 175  2017年12月 [査読有り][通常論文]
     
    Sporadic-E (Es) is a layer of ionization that irregularly appears within the E region of the ionosphere and is known to generate an unusual propagation of very high frequency waves over long distances. The detailed spatial structure of Es remains unclear due to the limited spatial resolution in the conventional ionosonde observations. We detect midlatitude Es by interferometric synthetic aperture radar (InSAR), which can clarify the spatial structure of Es with unprecedented resolution. Moreover, we use the range split-spectrum method (SSM) to separate dispersive and nondispersive components in the InSAR image. While InSAR SSM largely succeeds in decomposing into dispersive and nondispersive signals, our results indicate that small-scale dispersive signals due to the total electron content anomalies are accompanied by nondispersive signals with similar spatial scale at the same locations. We also examine the effects of higher-order terms in the refractive index for dispersive media. Both of these detected Es episodes indicate that smaller-scale dispersive effects originate from higher-order effects. We interpret that the smaller-scale nondispersive signals could indicate the emergence of nitric oxide (NO) generated by the reactions of metals, Mg and Fe, with nitric oxide ion (NO+) during the Es.
  • USMAN Muhammad, FURUYA Masato, SAKAKIBARA Daiki, ABE Takahiro
    雪氷研究大会講演要旨集 2017 186 - 186 公益社団法人 日本雪氷学会／日本雪工学会 2017年
  • 波多 俊太郎, 古屋 正人
    雪氷研究大会講演要旨集 2017 187 - 187 公益社団法人 日本雪氷学会／日本雪工学会 2017年
  • 福井 幸太郎, 藤田 耕史, ツェリン プンツォ, 古屋 正人
    雪氷研究大会講演要旨集 2017 89 - 89 公益社団法人 日本雪氷学会／日本雪工学会 2017年
  • Youhei Kinoshita, Masato Furuya
    Sola 13 0 79 - 84 2017年 [査読有り][通常論文]
     
    Localized propagation delay signals associated with linealigned convective cells were detected by the Synthetic Aperture Radar Interferometry (InSAR) technique on 25 August 2010 in Niigata prefecture. The maximum amplitude of the signal reached up to 22.5 cm, which was approximately equivalent to 29 mm anomaly in precipitable water vapor (PWV). The nationwide radar rainfall intensity captured the spatial distribution of hydrometeors on both land and sea, which was similar to that of the InSAR-derived water vapor field, suggesting that the convective cells were initiated on the Japan Sea to the west-southwest of the observation area. A numerical weather model (NWM) simulation with the grid spacing of 2.5 km reproduced line-aligned convective cells with 3 cm smaller maximum amplitude to that in InSAR. A NWM simulation that assimilates Global Navigation Satellite System (GNSS)-derived PWV data for four-dimensional variational assimilation enhanced the water vapor flux convergence at the surface, which improved the amplitude of the localized delay signals. The advantage of the unique water vapor observation by InSAR enabled us to assess the meso-gamma scale NWM reproducibility in terms of water vapor, which is one of the fundamental prognostic parameter for NWMs.
  • Masato Furuya
    Bulletin of Glaciological Research 35 7 - 17 2017年 [査読有り][通常論文]
  • Yuji Himematsu, Masato Furuya
    Earth, Planets and Space 68 1 2016年12月01日 [査読有り][通常論文]
     
    Series of earthquakes including three M w > 6 earthquakes occurred in Kumamoto prefecture in the middle of the Kyushu island, Japan. In order to reveal the associated crustal deformation signals, we applied offset tracking technique to ALOS-2/PALSAR-2 data covering three M w > 6 earthquakes and derived the 3D displacements around the epicenters. We could identify three NE-SW trending displacement discontinuities in the 3D displacements that were consistent with the surface location of Futagawa and Hinagu fault system. We set three-segment fault model whose positions matched the displacement discontinuities, and estimated the slip distributions on each segment from the observed pixel-offset data. Whereas right-lateral slip was dominant in the shallower depth of the larger segments, normal fault slip was more significant at a greater depth of the other segment. The inferred configuration and slip distribution of each segment suggest that slip partitioning under oblique extension stress regime took place during the 2016 Kumamoto earthquake sequence. Moreover, given the consistent focal mechanisms derived from both the slip distribution model and seismology, the significant non-double couple components in the focal mechanism of the main shock are due to simultaneous ruptures of both strike-slip and normal faulting at the distinct segments.
  • 阿部隆博, 古屋正人
    雪氷 78 6 425 - 438 日本雪氷学会 2016年11月 [査読有り][通常論文]
  • Himematsu, Y., Furuya, M.
    Earth Planets and Space 68 169  2016年 [査読有り][通常論文]
     
    Series of earthquakes including three M-w > 6 earthquakes occurred in Kumamoto prefecture in the middle of the Kyushu island, Japan. In order to reveal the associated crustal deformation signals, we applied offset tracking technique to ALOS-2/PALSAR-2 data covering three M-w > 6 earthquakes and derived the 3D displacements around the epicenters. We could identify three NE-SW trending displacement discontinuities in the 3D displacements that were consistent with the surface location of Futagawa and Hinagu fault system. We set three-segment fault model whose positions matched the displacement discontinuities, and estimated the slip distributions on each segment from the observed pixel-offset data. Whereas right-lateral slip was dominant in the shallower depth of the larger segments, normal fault slip was more significant at a greater depth of the other segment. The inferred configuration and slip distribution of each segment suggest that slip partitioning under oblique extension stress regime took place during the 2016 Kumamoto earthquake sequence. Moreover, given the consistent focal mechanisms derived from both the slip distribution model and seismology, the significant non-double couple components in the focal mechanism of the main shock are due to simultaneous ruptures of both strike-slip and normal faulting at the distinct segments.
  • Maeda, Jun, Suzuki, Takato, Furuya, Masato, Heki, Kosuke
    Geophysical Research Letters 43 4 1419 - 1425 2016年 [査読有り][通常論文]
     
    Kilometer-scale fine structures of midlatitude sporadic E (Es) plasma patches have been directly imaged for the first time by an interferogram derived from L band Advanced Land Observation Satellite/Phased Array-type L band Synthetic Aperture Radar data obtained over southwestern Japan. The synthetic aperture radar interferogram captured the eastern part of a large-scale frontal structure of daytime midlatitude Es which spans over 250 km in the east-northeast to west-southwest direction. Fine structures are characterized by frontal and disc-shaped patches which are elongated in the same direction as the large-scale frontal structure. Length and width of the disc-shaped patches are 10-20 km and 5-10km, respectively, and they are quasi-periodically located with a typical separation of 10-15km. The Kelvin-Helmholtz instability with the vertical shear of zonal winds is considered to be the most likely candidate for the generation mechanism of the frontal patch and disc-shaped patches aligned in the zonal direction.
  • Abe, Takahiro, Furuya, Masato, Sakakibara, Daiki
    Cryosphere 10 4 1427 - 1432 2016年 [査読有り][通常論文]
     
    Surge-type glaciers repeat their short active phase and their much longer quiescent phase usually every several decades or longer, but detailed observations of the evolution cycles have been limited to only a few glaciers. Here we report three surging episodes in 1989, 2001, and 2013 at Donjek Glacier in the Yukon, Canada, indicating remarkably regular and short repeat cycles of 12 years. The surging area is limited within the similar to 20 km section from the terminus, originating in an area where the flow width significantly narrows downstream, suggesting a strong control of the valley constriction on the surge dynamics.
  • T. Abe, M. Furuya, D. Sakakibara
    The Cryosphere Discuss 9 5943 - 5955 2015年11月 [査読有り][通常論文]
  • Yuji Himematsu, Masato Furuya
    Tectonophysics 656 52 - 60 2015年08月 [査読有り][通常論文]
     
    In July 2007, an earthquake swarm initiated in northern Tanzania near Lake Natron and lasted for about two months. Mt. Oldoinyo Lengai, located to the southwest of the swarm, began to erupt effusively about a month prior to the swarm, and increased its eruption intensity on September when the swarm almost ceased. Several previous studies have already reported the crustal deformation signals associated with the swarm using Interferometric Synthetic Aperture Radar (InSAR). However, nearly all the published data are based on the C-band ENVISAT/ASAR images acquired only from the descending path. We use the L-band ALOS/PALSAR images acquired from both ascending and descending paths, which allow us to examine the deformation signals in more detail. In addition to the InSAR data, we employ the offset-tracking technique to detect the signals along the azimuth direction. Using InSAR and offset-tracking data, we obtain the full 3D displacement fields associated with the episode. Besides the horizontal extension and subsidence signals due to the dike intrusion as already reported, the inferred full 3D displacements further indicate that the subsiding zone was horizontally moving by similar to 48 cm toward SSW. To explain the displacements, we performed fault source modeling, assuming an elastic half space. The fault slip distribution indicates that the contribution of the strike-slip component is about 20% of total moment release. Because almost all the focal mechanisms of earthquakes during the 2007 event indicate nearly pure normal faulting, aseismic strike-slip must have been responsible for the horizontal movement of the subsiding zone. The strike-slip at the shallowest depths suggests the presence of transtensive stress, which seems to be reasonable to generate the relay zones that are widely observed in the East African Rift. We also confirmed that the stress changes due to the dike intrusion were consistent with the inferred fault slip distributions. (C) 2015 Elsevier B.V. All rights reserved.
  • 阿部 隆博, 古屋 正人, 榊原 大貴
    雪氷研究大会講演要旨集 2015 7 - 7 公益社団法人 日本雪氷学会／日本雪工学会 2015年
  • 阿部 隆博, 古屋 正人
    雪氷研究大会講演要旨集 2015 8 - 8 公益社団法人 日本雪氷学会／日本雪工学会 2015年
  • Yasuda, Takatoshi, Furuya, Masato
    Journal of Geophysical Research-Earth Surface 120 11 2393 - 2405 2015年 [査読有り][通常論文]
     
    Here we examine 31 glaciers in the West Kunlun Shan of the northwestern Tibetan Plateau and identify 9 as surge type. The method is based on satellite synthetic aperture radar and Landsat optical images, the former going back to 1992, the latter to 1972. To identify surge-type glaciers, we consider temporal changes in velocity, changes in glacier terminus position, propagation of a surge bulge, presence of looped and/or contoured medial moraines, and extensive crevassing. Other than the nine surge-type glaciers, we identify two that have likely surged, and six that may be surge type. But no glacier surges more than once during the observation period, meaning that the recurrence interval exceeds 42 years. In addition, we examine the evolution of the surface velocities at two surging glaciers with the unprecedented temporal resolution of down to 11 days over similar to 7 years. The results show clear seasonal modulations by as much as similar to 200% in early winter against those in early summer. This seasonal modulation in surface velocity suggests the presence of surface meltwater that reroutes through the englacial and subglacial drainage systems. Thus, our findings suggest that the hydrological processes originating in the surface meltwater play an important role in maintaining the yearlong active surging phase.
  • Usman, Muhammad, Furuya, Masato
    Earth Planets and Space 67 2015年 [査読有り][通常論文]
     
    The Quetta Syntaxis in western Baluchistan, Pakistan, is the result of an oroclinal bend of the western mountain belt and serves as a junction for different faults. As this area also lies close to the left-lateral strike-slip Chaman fault, which marks the boundary between the Indian and Eurasian plates, the resulting seismological behavior of this regime is very complex. In the region of the Quetta Syntaxis, close to the fold and thrust belt of the Sulaiman and Kirthar Ranges, an earthquake with a magnitude of 6.4 (Mw) occurred on October 28, 2008, which was followed by a doublet on the very next day. Six more shocks associated with these major events then occurred (one foreshock and five aftershocks), with moment magnitudes greater than 4. Numerous researchers have tried to explain the source of this sequence based on seismological, GPS, and Environmental Satellite (ENVISAT)/Advanced Synthetic Aperture Radar (ASAR) data. Here, we used Advanced Land Observing Satellite (ALOS)/Phased Array-type L-band Synthetic Aperture Radar (PALSAR) InSAR data sets from both ascending and descending orbits that allow us to more completely detect the deformation signals around the epicentral region. The results indicated that the shock sequence can be explained by two right-lateral and two left-lateral strike-slip faults that also included reverse slip. The right-lateral faults have a curved geometry. Moreover, whereas previous studies have explained the aftershock crustal deformation with a different fault source, we found that the same left-lateral segment of the conjugate fault was responsible for the aftershocks. We thus confirmed the complex surface deformation signals from the moderate-sized earthquake. Intra-plate crustal bending and shortening often seem to be accommodated as conjugate faulting, without any single preferred fault orientation. We also detected two possible landslide areas along with the crustal deformation pattern.
  • Abe, T., Furuya, M.
    Cryosphere 9 3 1183 - 1190 2015年 [査読有り][通常論文]
     
    Glacier surges often initiate in winter, but the mechanism remains unclear in contrast to the well-known summer speed-up at normal glaciers. To better understand the mechanism, we used radar images to examine spatial-temporal changes in the ice velocity of surge-type glaciers near the border of Alaska and the Yukon, focusing on their quiescent phase. We found significant accelerations in the upstream region from autumn to winter, regardless of surging episodes. Moreover, the winter speed-up propagated from upstream to downstream. Given the absence of surface meltwater input in winter, we suggest the presence of water storage near the base that does not directly connect to the surface, yet can promote basal sliding through increased water pressure. Our findings have implications for the modelling of glacial hydrology in winter, which may help us better understand glacier dynamics.
  • T. Abe, M. Furuya
    The Cryosphere Discuss 8 2611 - 2635 2014年05月 [査読有り][通常論文]
  • Youhei Kinoshita, Masanobu Shimada, Masato Furuya
    Geophysical Research Letters 40 17 4740 - 4744 2013年09月06日 [査読有り][通常論文]
     
    This study reports the first detection and analysis of a localized water vapor distribution obtained using interferometric synthetic aperture radar (InSAR) during the Seino heavy rain episode. The InSAR data retrieved during the ALOS/PALSAR emergency observations for the event revealed a radar line-of-sight (LOS) change of up to 130mm within 10km. Based on the signal, we estimated the three-dimensional water vapor distribution using the ray-tracing method, which indicated a column of nearly saturated water vapor within a 10km(2) area reaching from the surface to 9000m above ground level. To geophysically confirm this signal, Weather Research and Forecasting (WRF) model simulations were performed, revealing a deep convection that was initiated by orographic lift caused by the Yoro Mountains. Another simulation that did not include the Yoro Mountains did not produce a deep convection. The WRF simulation also suggested that the effect of hydrometeors can account for approximately 20% of the maximum LOS change but this effect is even more localized than the effect of water vapor.
  • Furuya, Masato, Hobiger, Thomas, Ichikawa, Ryuichi, Kinoshita, Youhei
    Journal of Geodesy 87 3 267 - 277 2013年 [査読有り][通常論文]
     
    Interferometric synthetic aperture radar phase data include not only signals due to crustal movements, but also those associated with microwave propagation delay through the atmosphere. In particular, the effect of water vapor can generate apparent signals in the order of a few centimeters or more, and prevent us from detecting such geophysical signals as those due to secular crustal deformation. To examine if and to what extent numerical weather model (NWM) outputs are helpful to reduce the tropospheric delay signals at spatial scales of 5-50 km wavelengths, we compared three approaches of tropospheric signal reduction, using 54 interferograms in central Hokkaido, Japan. The first approach is the conventional topography-correlated delay correction that is based on the regional digital elevation model (DEM). The second approach is based on the Japan Meteorological Agency's operational meso-scale analysis model (MSM) data, where we compute tropospheric delays and subtract them from the interferogram. However, the MSM data are available at predefined epochs and their spatial resolution is about 10 km; therefore, we need to interpolate both temporally and spatially to match with interferograms. Expecting to obtain a more physically plausible reduction of the tropospheric effects, we ran a 1-km mesh high-resolution numerical weather model WRF (Weather Research and Forecasting model) by ourselves, using the MSM data as the initial and boundary conditions. The third approach is similar to the second approach, except that we make use of the WRF-based tropospheric data. Results show that if the topography-correlated phases are significant, both the conventional DEM-based approach and the MSM-based approach reveal comparable performances. However, when the topography-correlated phases are insignificant, none of the approaches can efficiently reduce the tropospheric phases. Although it could reduce the tropospheric signals in a local area, in none of the case studies did the WRF model produce the "best" performance. Whereas the global atmospheric model outputs are shown to be effective in reducing long-wavelength tropospheric signals, we consider that further improvements are needed for the initial and boundary condition data for high-resolution NWM, so that the NWM-based approach will become more reliable even in the case of a non-stratified troposphere.
  • Abe, Takahiro, Furuya, Masato, Takada, Youichiro
    Bulletin of the Seismological Society of America 103 1 507 - 518 2013年 [査読有り][通常論文]
     
    We use crustal deformation data sets acquired by the Phased Array-Type L-Band Synthetic Aperture Radar (PALSAR) and the Japanese nationwide Global Positioning System (GPS) Earth Observation Network (GEONET) to develop a fault source model for the 2008 Iwate-Miyagi inland earthquake (M-w 6.9) that occurred on 14 June 2008 in northeastern Honshu, Japan. The PALSAR data include Interferometric Synthetic Aperture Radar (InSAR), range offset, and azimuth offset acquired from both ascending and descending paths. The range- and azimuth-offset data are the only quantitative deformation signals around the epicenter, and exhibit complicated signals that were not detected by the GPS data. We refine our preliminary model by using Green's functions from triangular dislocation elements to represent nonplanar fault geometries. Although a single segment model can well explain the GPS data, it generates significant misfit residuals in the offset data; thus, both west-dipping and east-dipping segments are necessary, as also suggested from aftershock distribution data. The moment magnitudes of the west-dipping and east-dipping faults are 6.53 and 6.76, respectively, and the total sum, 6.87, is almost identical to the seismological moment magnitude. This result suggests that both segments contributed equally to the total seismic moment, demonstrating a complex rupture process of the inland earthquake.
  • Furuya, Masato, Yasuda, Takatoshi
    Remote Sensing of Environment 128 87 - 106 2013年 [査読有り][通常論文]
     
    Seasonal glacier velocity changes across the High Arctic, including the Greenland Ice Sheet, have been observed and have attracted significant attention over the past decade. However, it remains uncertain how much short-term variability exists in other polythermal glaciers, particularly those in High Asia. Here we report satellite radar image analyses that reveal diverse glacier surface velocities and their evolution in West Kunlun Shan (WKS), NW Tibet, where little is known about glacier dynamics. On the basis of radar images obtained from 2003 to 2011, we examined 36 glaciers, and classified them into two classes according to their multi-temporal velocity profiles: 25 as normal-flow type (surface velocity reaches maxima around the middle part, and gradually approaches zero toward downstream and upstream), and four as surging type (surface velocities are greater than 150 m/yr, and/or the terminus advance is recognized from the radar images). Seven other glaciers do not fit the former two classes, and reveal stagnant velocity profiles that are nearly zero in the lower part but are similar to those of the normal type in the upper part. Although these glaciers could be just stagnant tongues indicative of receding normal type glaciers, given the temporal evolution at the Zhongfeng Glacier, the stagnant type possibly represents a quiescent phase of the surging type glaciers. While glacier surfaces are mostly clean with limited debris-cover, except near the termini, surge-type glaciers might be common in WKS. The observed short-term velocity changes provide us with evidence for efficient basal slip even at the high-elevation polythermal glaciers. This study demonstrates that frequent radar image acquisitions are helpful to understand short-term velocity changes at remote glaciers in detail. Crown Copyright (C) 2012 Published by Elsevier Inc. All rights reserved.
  • Youhei Kinoshita, Masanobu Shimada, Masato Furuya
    CONFERENCE PROCEEDINGS OF 2013 ASIA-PACIFIC CONFERENCE ON SYNTHETIC APERTURE RADAR (APSAR) 175 - + 2013年 [査読有り][通常論文]
     
    This study reports the first detection and analysis of a localized water vapor distribution during Seino heavy rain episode by Interferometric Synthetic Aperture Radar (InSAR). The InSAR data retrieved during ALOS/PALSAR emergency observations for the event revealed a radar line-of-sight change of up to 130 mm within 10 km. Based on the signal, we estimated a three-dimensional water vapor distribution using the ray-tracing method, which indicated a column of nearly saturated water vapor within a 10 km(2) from the surface to 9000 m above ground level. To geophysically confirm this signal, Weather Research and Forecasting (WRF) model simulations were performed, and consequently suggesting the deep convection initiated by orographic lift of the Yoro Mountains 20 km south of the localized signal. On receiving results of WRF simulations, another simulation was performed without data of the Yoro Mountains, which did not reveal a deep convection. These results demonstrated the importance of realistic topography in the simulation of mesoscale convective systems.
  • Kaneko Y., Fialko Y., Sandwell D. T., Tong X., Furuya M.
    Journal of Geophysical Research - Solid Earth 118 1 316 - 331 American Geophysical Union 2013年 [査読有り][通常論文]
     
    We present high-resolution measurements of interseismic deformation along the central section of the North Anatolian Fault (NAF) in Turkey using interferometric synthetic aperture radar data from the Advanced Land Observing Satellite and Envisat missions. We generated maps of satellite line-of-sight velocity using five ascending Advanced Land Observing Satellite tracks and one descending Envisat track covering the NAF between 31.2 degrees E and 34.3 degrees E. The line-of-sight velocity reveals discontinuities of up to similar to 5 mm/yr across the Ismetpasa segment of the NAF, implying surface creep at a rate of similar to 9 mm/yr; this is a large fraction of the inferred slip rate of the NAF (21-25 mm/yr). The lateral extent of significant surface creep is about 75 km. We model the inferred surface velocity and shallow fault creep using numerical simulations of spontaneous earthquake sequences that incorporate laboratory-derived rate and state friction. Our results indicate that frictional behavior in the Ismetpasa segment is velocity strengthening at shallow depths and transitions to velocity weakening at a depth of 3-6 km. The inferred depth extent of shallow fault creep is 5.5-7 km, suggesting that the deeper locked portion of the partially creeping segment is characterized by a higher stressing rate, smaller events, and shorter recurrence interval. We also reproduce surface velocity in a locked segment of the NAF by fault models with velocity-weakening conditions at shallow depth. Our results imply that frictional behavior in a shallow portion of major active faults with little or no shallow creep is mostly velocity weakening. Citation: Kaneko, Y., Y. Fialko, D. T. Sandwell, X. Tong, and M. Furuya (2013), Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey): InSAR observations and implications for rate-and-state friction properties, J. Geophys. Res. Solid Earth, 118, 316-331, doi: 10.1029/2012JB009661.
  • Minami Muto, Masato Furuya
    Remote Sensing of Environment 139 50 - 59 2013年 [査読有り][通常論文]
     
    The Patagonian Ice Fields are known to have undergone rapid retreat of frontal positions and significant thinning of its glaciers over the past decades. However, surface velocities have been measured at only a few of these glaciers. Thus, it remains uncertain if and to what extent the glacier dynamics has changed over time and contributed to ice loss in these ice fields. In this study, we examine the temporal evolution of flow velocities and ice-front positions at eight major glaciers in the Southern Patagonian Ice Field (SPI; Hielo Patagonico Sur) by using Advanced Synthetic Aperture Radar (ASAR) images from the Environmental Satellite (Envisat) launched in 2002 by the European Space Agency and Advanced Land Observation Satellite/Phased Array-type L-band Synthetic Aperture Radar (ALOS/PALSAR) data recorded from 2002 to 2011. The examined eight glaciers include Glaciar Jorge Montt, Occidental, Pio XI (or Briiggen), O'Higgins, Viedma, Upsala, Perito Moreno, and Grey. Not all the glaciers revealed significant changes in frontal positions and flow velocities in the study period. We detected significant temporal velocity changes at Glaciar Upsala, Jorge Montt, Occidental, and Pio XI. Among these four glaciers, Glaciars Upsala, Jorge Montt, and Occidental revealed significant acceleration and terminus retreat and were undergoing dynamic-thinning. The markedly different absolute velocities but equally large longitudinal near-terminus stretching at the three glaciers support a calving model based on crevasse-depth criteria, which predict a calving position where crevasse-depths are equal to ice thickness; crevasse-depths are controlled by the longitudinal stretching rate. Meanwhile, Glaciar Pio XI revealed complex spatial and temporal evolution in surface velocities without significant retreat, and its dynamics remains enigmatic. (C) 2013 Elsevier Inc. All rights reserved.
  • Lin Liu, John Wahr, Ian Howat, Shfaqat Abbas Khan, Ian Joughin, Masato Furuya
    Geophysical Journal International 188 3 994 - 1006 2012年01月09日 [査読有り][通常論文]
     
    Jakobshavn Isbre in west Greenland has been undergoing dramatic thinning since 1997. Applying the interferometric synthetic aperture radar (InSAR) technique to Radarsat-1 SAR data, we measure crustal uplift near Jakobshavn Isbr caused by recent ice mass loss. The crustal uplift is predominantly at long spatial wavelengths (larger than 10 km), and thus is difficult to separate from InSAR orbit errors. We reduce the effects of orbit errors by removing long-wavelength deformation signals using conventional InSAR baseline fitting methods. We find good agreement between the remaining short-scale InSAR-estimated deformation rates during 20042008 and the corresponding short-scale components of a deformation model that is based on changes in ice elevation measured by NASAs Airborne Topographic Mapper (ATM). We are also able to use the InSAR-measured deformation to invert for the spatial pattern of ice thinning. Overall, our results suggest that despite the inherent difficulties of working with a signal that has significant large-scale components, InSAR-measured crustal deformation can be used to study the ice mass loss of a rapidly thinning glacier and its surrounding catchment, providing both a constraint on any existing model of ice mass loss and a data source that can be used to invert for ice mass loss. These new applications of InSAR can help to better understand a glaciers rapid response to a warming climate.
  • 阿部 隆博, 古屋 正人
    雪氷研究大会講演要旨集 2012 5 - 5 公益社団法人 日本雪氷学会／日本雪工学会 2012年
  • 安田 貴俊, 古屋 正人
    雪氷研究大会講演要旨集 2012 2 - 2 公益社団法人 日本雪氷学会／日本雪工学会 2012年
  • 高田 陽一郎, 小林 知勝, 古屋 正人, 村上 亮
    測地学会誌 57 4 181 - 193 The Geodetic Society of Japan 2011年 [査読有り][通常論文]
     
    We detected post-seismic surface deformation following the 2008 Iwate-Miyagi Nairiku Earthquake (2008 June 14 JST, M6.8) by interferometric synthetic aperture radar (InSAR) analysis using ALOS/PALSAR data. The ascending interferograms indicate ∼8 cm of length increase in radar line-of-sight (LOS) to the east of Mt. Kurikoma (KRK), and decreases in it to the south of KRK and around Mt. Amadamori (AMM). The descending interferograms indicate ~4 cm of length increase in LOS to the east of Mt. Kunimiyama (KNM), and around AMM. We found that a west-dipping high-angle reverse fault roughly explains overall pattern of the length changes in LOS (ΔLOS) to the east of KNM. We demonstrated that ALOS/PALSAR has a strong ability to detect surface deformation lurking in such a vast mountainous area.
  • Furuya, Masato, Yasuda, Takatoshi
    Tectonophysics 511 3-4 125 - 133 2011年 [査読有り][通常論文]
     
    The ENE striking Altyn-Tagh Fault and the WNW striking Karakax Fault are two major strike-slip fault systems in northern Tibet, and form a prominent similar to 2000 km long fault system. The 2008 Yutian normal faulting earthquake (Mw 7.1) struck near the southern edge of the Tarim Basin, where the two fault systems converge. While there are numerous NS-trending normal faults particularly in southern Tibet, their tectonic origins have remained contentious. Based on crustal deformation data sets obtained from synthetic aperture radar (SAR) as well as aftershock distribution, we developed a non-planar fault source model for the 2008 Yutian earthquake that exhibits a large normal-fault slip on a west-dipping surface with a nearly NS strike, thus suggesting a localized EW trending extensional stress field. The extensional stress was presumably generated at a step-over region of two NE-trending left-lateral strike-slip faults, which would probably belong to the Altyn-Tagh and Longmu-Gozha Co Fault Systems. In the epicentral area, there exists a fault scarp that coincides with the top edge of our fault model, and thus similar earthquakes must have occurred over geological time. Such normal faulting earthquakes must have been repeatedly suppressed the left-lateral slip behavior of the Karakax Fault. In addition, if the slip along the Altyn-Tagh Fault is transferred to the Longmu-Gozha Co Fault, which is SE across the normal fault system, the slip rate of the Karakax Fault would be less than that of the adjoining Altyn-Tagh Fault. (C) 2011 Elsevier B.V. All rights reserved.
  • 村上 亮, 奥山 哲, 古屋 正人, 阿部 隆博
    日本火山学会講演予稿集 2011 55 - 55 特定非営利活動法人 日本火山学会 2011年
  • Yoshiyuki Tanaka, Aitaro Kato, Takayuki Sugano, Guangyu Fu, Xinlin Zhang, Masato Furuya, Wenke Sun, Shuhei Okubo, Shigeo Matsumoto, Masaki Honda, Yasuhiro Sugawara, Isao Ueda, Masaaki Kusaka, Misao Ishihara
    EARTH PLANETS AND SPACE 62 12 905 - 913 2010年 [査読有り][通常論文]
     
    Slow-slip events (SSEs) have been observed in many plate-boundary zones along the circum-Pacific seismic belt. Previous studies have revealed that high-pressure fluids supplied from the subducted oceanic plate can generate SSEs. However, the behavior of these fluids during an SSE has not been fully elucidated. This paper discusses possible fluid migration along the plate boundary on the basis of spatiotemporal gravity changes observed by absolute and relative gravimeters during a long-term SSE in the Tokai district, Japan. Relative-gravity data are sometimes unreliable because of limited observation accuracies and possible noise produced by groundwater. Nevertheless, the observed gravity changes show a systematic pattern of spatial changes over the slow-slip area. This pattern can be explained by a poroelastic model assuming fluid migration along the plate interface, for which an inversion indicates a permeability of about 10(-15) m(2). This lies within the range of permeability values inferred by other studies in slow-slip areas. Long-term SSEs have occurred repeatedly in the Tokai district. If the permeability remains greater than 10(-15) m(2) during a future SSE, it will be possible to detect fluid migration by improving the observation accuracy to the 1-mu Gal level and accurately evaluating groundwater-related noise.
  • Furuya, M., Kobayashi, T., Murakami, M., Takada, Y.
    Bulletin of the Seismological Society of America 100 5B 2750 - 2766 2010年 [査読有り][通常論文]
     
    We use crustal deformation data sets derived from satellite-based synthetic aperture radar (SAR) to develop a fault source model of the 2008 M-w 7.9 Wenchuan earthquake, China, that occurred at the Longmen Shan fault zone. The data sets include interferometric SAR (InSAR), range offset, and azimuth offset data acquired at seven ascending paths. The range and azimuth offset data are particularly important, exhibiting a single major rupture to the northeast (NE) and multiple ruptures to the southwest (SW). Our preferred model consists of six segments; four follow the previously mapped traces of the Beichuan fault (BF) and its NE extension, one corresponds to the Pengguan fault (PF) to the SW, and the other is included to represent a conjugate fault to the SW. Fixing the location and geometry of those segments, we solve the variable slip distribution whose patch size increases toward the greater depth; we use a nonnegative least-squares method with a smoothing constraint on the distributed slip. The geodetically estimated moment is 1.05 x 10(21) N m (M-w = 7.9), which is close to the seismological estimate and suggests that there are insignificant postseismic signals in the data. Maximum slip of similar to 10 m, consisting of both thrust and right-lateral slip components, is identified at the shallowest patches to the NE along the BF. The multiple fault segments to the SW show that the thrust slip component initially dominates, and the strike slip becomes significant toward the NE. Examining the sensitivity of the predicted azimuth offset data to the assumed dip angle, we found that the dip angle changed significantly from 35 degrees-45 degrees at the SW fault segment for the PF to 80 degrees-90 degrees at the NE extension of the BF.
  • M. Furuya, Y. Takada, Y. Aoki
    GRAVITY, GEOID AND EARTH OBSERVATION 135 679 - 687 2010年 [査読有り][通常論文]
     
    On June 16 2007 (AM 10: 13 in Japan Standard Time), an earthquake of magnitude 6.8 took place about 10 km offshore of Chuetsu area in Niigata, Japan. Using L-band PALSAR InSAR (Interferometric Synthetic Aperture Radar) data, we could detect not only coseismic broad deformation but also significant aseismic deformation nearly 15 km away from the epi-center along an anticline axis. They mostly turned out to terminate within 3 days after the earthquake. The aseismic slip was modeled by a combination of west-dipping fault and east-dipping fault, which appear to be detachment faults on the western and eastern flank of the anticline. The moment magnitude released by the aseismic slip is estimated to be M-w 5.98. This observation demonstrates that a fault-related fold grows aseismically, and therefore seismic hazard is actually low for this particular fold. Although there is a dense GPS network in Japan, we should note that the aseismic signal was only detectable by InSAR data. http://download.springer.com/static/pdf/469/chp%253A10.1007%252F978-3-642-10634-7_89.pdf?originUrl=http%3A%2F%2Flink.springer.com%2Fchapter%2F10.1007%2F978-3-642-10634-7_89&token2=exp=1495880879acl=%2Fstatic%2Fpdf%2F469%2Fchp%25253A10.1007%25252F978-3-642-10634-7_89.pdf%3ForiginUrl%3Dhttp%253A%252F%252Flink.springer.com%252Fchapter%252F10.1007%252F978-3-642-10634-7_89*hmac=4147be0408c3199c2f47ce2917b5de1839a411258e08c4478e92d41199e22757
  • Furuya, M., Hobiger, T., Ichikawa, R., Kinoshita, Y., Kondo, T., Koyama, Y., Shimizu, S.
    Journal of Geodesy 84 9 537 - 546 2010年 [査読有り][通常論文]
     
    Numerical weather models offer the possibility to compute corrections for a variety of space geodetic applications, including remote sensing techniques like interferometric SAR. Due to the computational complexity, exact ray-tracing is avoided in many cases and mapping approaches are applied to transform vertically integrated delay corrections into slant direction. Such an approach works well as long as lateral atmospheric gradients are small enough to be neglected. But since such an approximation holds only for very rare cases it is investigated how horizontal gradients of different atmospheric constituents can evoke errors caused by the mapping strategy. Moreover, it is discussed how sudden changes of wet refractivity can easily lead to millimeter order biases when simplified methods are applied instead of ray-tracing. By an example, based on real InSAR data, the differences of the various troposphere correction schemes are evaluated and it is shown how the interpretation of the geophysical signals can be affected. In addition, it is studied to which extend troposphere noise can be reduced by applying the exact ray-tracing solution.
  • Furuya, M., Takada, Y.
    Earth and Planetary Science Letters 290 3-4 302 - 310 2010年 [査読有り][通常論文]
     
    In August 1996, an earthquake swarm including 4 earthquakes of magnitudes greater than 5 occurred in and around the Onikobe geothermal area, northeast Japan. While earlier studies detected ground displacements by L-band JERS radar interferograms, there remained certain puzzling discrepancies between the observations and the predictions from a seismologically inferred model, and no satisfactory models have yet been proposed. Here, by identifying that a steep gradient in the radar line-of-sight changes exists in seismicity gaps to the east and west of the Torage area Oust to the north of the Onikobe caldera), we propose two aseismic reverse faults, which turn out to contribute to a local topographic growth as well as explaining the pre-existing discrepancies. Another significant signal is detected in a region in which no large earthquakes occurred; we account for this signal by another aseismic fault. This fault adds to another evidence for the recent hypothesis that aseismic fault motion drives earthquake swarm. (C) 2009 Elsevier B.V. All rights reserved.
  • Yoshiyuki Tanaka, Aitaro Kato, Takayuki Sugano, Guangyu Fu, Xinlin Zhang, Masato Furuya, Wenke Sun, Shuhei Okubo, Shigeo Matsumoto, Masaki Honda, Yasuhiro Sugawara, Isao Ueda, Masaaki Kusaka, Misao Ishihara
    Earth, Planets and Space 62 12 905 - 913 2010年 [査読有り][通常論文]
     
    Slow-slip events (SSEs) have been observed in many plate-boundary zones along the circum-Pacific seismic belt. Previous studies have revealed that high-pressure fluids supplied from the subducted oceanic plate can generate SSEs. However, the behavior of these fluids during an SSE has not been fully elucidated. This paper discusses possible fluid migration along the plate boundary on the basis of spatiotemporal gravity changes observed by absolute and relative gravimeters during a long-term SSE in the Tokai district, Japan. Relativegravity data are sometimes unreliable because of limited observation accuracies and possible noise produced by groundwater. Nevertheless, the observed gravity changes show a systematic pattern of spatial changes over the slow-slip area. This pattern can be explained by a poroelastic model assuming fluid migration along the plate interface, for which an inversion indicates a permeability of about 10-15 m2. This lies within the range of permeability values inferred by other studies in slow-slip areas. Long-term SSEs have occurred repeatedly in the Tokai district. If the permeability remains greater than 10-15 m2 during a future SSE, it will be possible to detect fluid migration by improving the observation accuracy to the 1-μGal level and accurately evaluating groundwater-related noise. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Science (SGEPSS).
  • Tomokazu Kobayashi, Youichiro Takada, Masato Furuya, Makoto Murakami
    GEOPHYSICAL RESEARCH LETTERS 36 2009年04月 [査読有り][通常論文]
     
    We have detected detailed ground displacements in the proximity of the Longmen Shan fault zone (LMSFZ) by applying a SAR offset-tracking method in the analysis of the 2008 Sichuan earthquake. An elevation-dependent correction is indispensable for achieving sub-meter accuracy. A sharp displacement discontinuity with a relative motion of similar to 1-2 m appears over a length of 200 km along the LMSFZ, which demonstrates that the main rupture has proceeded on the Beichuan fault (BF) among several active faults composing the LMSFZ, and a new active fault is detected on the northeastward extension of the BF. The rupture on the BF is characterized by a right-lateral motion in the northeast, while in the southwest an oblique right-lateral thrust slip is suggested. In contrast to the northeast, where a major rupture proceeded on the BF only, in the southwest multiple thrust ruptures have occurred in the southeastern foot of the Pengguan massif. Citation: Kobayashi, T., Y. Takada, M. Furuya, and M. Murakami (2009), Locations and types of ruptures involved in the 2008 Sichuan earthquake inferred from SAR image matching, Geophys. Res. Lett., 36, L07302, doi:10.1029/2008GL036907.
  • Furuya, Masato, Kobayashi, Tomokazu, Murakami, Makoto, Takada, Youichiro
    Earth Planets and Space 61 4 e9 - e12 2009年 [査読有り][通常論文]
     
    Applying interferometric SAR (InSAR) analysis to the 2008 Iwate-Miyagi Nairiku earthquake, we detected notable ground displacements of several tens of centimeters to about 1.2 m that extend further south of the epicentral area. We explained the InSAR data by constructing a fault model consisting of four WNW dipping and one ESE dipping reverse faults. The residuals between observed and modeled deformation are less than 6 cm in most of the area, which is comparable to the errors caused by atmospheric effect. To fill the lack of InSAR data in the hypocentral area, we applied a pixel matching technique to the intensity images, which shows a shortening in range offsets by as much as similar to 2 m along a narrow zone stretching along the eastern foot of Mt. Kurikoma, indicating a localized uplift. We also found remarkable contrasts in the range offsets around the low coherence area equivalent to a very large displacement gradient to the WNW of the hypocentral area as well as ESE. We conclude that the main faulting occurred on the WNW dipping reverse faults, but that the overall geometry of the fault system is quite complex including at least one conjugate faulting, as also supported by the hypocentral distribution of aftershocks.
  • Coseismic deformation due to the 2007 Chuetsu-oki earthquake (M(w)=6.8)
    Aoki, Y., Furuya, M., Kato, T.
    Earth Planets and Space 60 11 1075 - 1080 2008年 [査読有り][通常論文]
  • Furuya, M., Satyabala, S. P.
    Geophysical Research Letters 35 6 L06309  2008年 [査読有り][通常論文]
     
    The Chaman fault system forms a prominent similar to 900-km long left-lateral transform plate boundary between the Indian and Eurasian plates in Afghanistan and Pakistan. Here we show satellite radar interferometry data that revealed an afterslip (or slow earthquake) signal following an earthquake of magnitude 5.0. This slow slip episode lasted for more than a year, and accompanied a widespread creep signal that occurred at least similar to 50 km along the fault. We detected no surface slip before the earthquake during the 1.5 years sampled by our data. This finding of long-lasting widespread afterslip demonstrates that the plate motion along the Chaman Fault is accommodated by slow slip episodes following moderate earthquakes, and suggests that a potential for magnitude 7-class earthquakes was significantly reduced. The duration and moment release of the detected afterslip do not fit the recently proposed scaling law for slow earthquakes.
  • Masanobu Shimada, Taku Ozawa, Yo Fukushima, Masato Furuya, Ake Rosenqvist
    Eos, Transactions American Geophysical Union 89 31 277 - 277 2008年 [査読無し]
  • 及川 純, 青木 陽介, 古屋 正人, 井口 正人
    日本火山学会講演予稿集 2008 73 - 73 特定非営利活動法人 日本火山学会 2008年
  • Yosuke Aoki, Masato Furuya, Teruyuki Kato
    Earth, Planets and Space 60 11 1075 - 1080 2008年 [査読有り][通常論文]
     
    Global Positioning System (GPS) and Synthetic Aperture Radar Interferometry (InSAR) detected substantial ground deformation due to the 2007 Chuetsu-oki earthquake (Mw = 6.8) GPS observation detected a horizontal deformation of up to about 170 mm and subsidence of up to 30 mm, and InSAR detected up to 290 mm of line-of-sight changes. A fault model is proposed to fit the ground deformation field as well as the aftershock distribution. Our model shows that a northwest-dipping fault to the north and a southeast-dipping fault to the south, consistent with the aftershock distribution, fits well with the observed data. However, our model also suggests that the modeled faults are likely to extend to shallower depths, where aftershocks are terminated. Combining our model with the subsurface structure suggests that the earthquake rupture initiated at depth and propagated into shallower depths that are not capable of nucleating an earthquake because of the presence of unconsolidated sediments. Copyright © The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS) The Seismological Society of Japan The Volcanological Society of Japan The Geodetic Society of Japan The Japanese Society for Planetary Sciences TERRAPUB.
  • Application of Application of Interferometric Point Target Analysis to Izu-Oshima Volcano, Japan
    Proceedings of Envisat Symposium 2007 (CDROM) 462406  2007年 [査読無し][通常論文]
  • Furuya, M., Mueller, K., Wahr, J.
    Journal of Geophysical Research-Solid Earth 112 B6 B06418  2007年 [査読有り][通常論文]
     
    The Needles District in Canyonlands National Park, Utah, is known for its well-exposed array of extensional faults, which are thought to be produced by gravity-driven extension and downward flexure of a thin sandstone plate into the Colorado River canyon in response to dissolution and flow of underlying evaporites (halite and gypsum). Owing to a lack of precise geodetic data, however, it remains uncertain if and to what extent those extensional faults are currently deforming. In this study we use synthetic aperture radar (SAR) data to search for ongoing, decadal ground displacements, by applying both a stacking interferometric SAR (InSAR) analysis and Interferometric Point Target Analysis (IPTA). Our results show that most of the Needles District is indeed undergoing deformation now at a maximum rate of 2-3 mm/year away from the satellite, looking roughly westward with an incidence angle of about 20 degrees. Also, we identify a localized region along the riverbank that is uplifting at a rate of 2-3 mm/year. We estimate the measurement precision to be better than 0.8 mm/year, except along the riverbank where the errors are probably higher than this, by analyzing residual signals and carrying out a signal recovery experiment using synthetic two dimensional correlated noise. The deforming region is almost totally bounded by the Colorado River canyon to the west and north, a rapidly subsiding, east-west trending graben to the south, and a relatively sharp to very diffuse deformation gradient to the east. We observe deformation patterns that were previously undetected. These include an area in the southwestern part of the deforming region that is deforming at higher rates than anywhere else in the Needles but that has little surface extensional faulting. Rates of deformation are lower but still clearly significant further north, in a region of spectacularly exposed fault blocks that have been previously studied in considerable detail.
  • 古屋 正人
    測地学会誌 52 4 225 - 243 The Geodetic Society of Japan 2006年 [査読有り][通常論文]
     
    Interferometric Synthetic Aperture Radar (InSAR) provides us with images of crustal de formation with unprecedented spatial resolution. Its measurement precision is comparable to ground-based space geodetic techniques. Here I review how SAR data is acquired and proc essed to generate InSAR images. First, I describe in detail how raw SAR signal data are proc essed to generate geophysically interpretable image called single look complex (SLC) data. After introducing an image co-registration (matching) technique, I describe a principle of InSAR image generation, actual processing steps, and how to interpret them with potential issues to overcome. I also discuss interferometric coherence, which is another important concept that should be kept in mind. A couple of recent new applications results are explained, some which could not be obtained unless SAR data acqusition continued almost a decade. Further, new analysis techniques, i.e., permanent scatterer (PS) InSAR and ScanSAR, are briefly introduced. Finally, I discuss how promising the newly acquired L-band SAR data by Advanced Land Observation Satellite (ALOS) is for crustal deformation measurement.
  • FURUYA M.
    Cahiers du Centre European de Geodynmique et de Seismologie 24 57 - 59 2005年 [査読有り][通常論文]
  • Furuya, M., Wahr, J. M.
    Geophysical Research Letters 32 14 L14501  2005年 [査読有り][通常論文]
     
    We detect ground displacements around an ice-dammed lake (Lake Tiningnilik) in west Greenland, using ERS1/2 and Envisat radar interferograms. We associate those displacements with draining episodes (jokulhlaups in Icelandic) that occurred in 1993 and 2003. We confirm those episodes in backscatter intensity images. By assuming a 7.5 meter/year increase in water level and using an elastic loading model, we predict a rate and spatial pattern for the deformation that are in good agreement with the observations. By generating digital elevation models from radar interferograms for both the drained and undrained stages, we validate the inferred lake level changes.
  • Furuya, M.
    Geophysical Journal International 161 1 230 - 242 2005年 [査読有り][通常論文]
     
    We derive closed analytical solutions for quasi-static thermoelastic deformation in response to instantaneous point and spherical heat sources in an elastic half-space. Since we can take advantage of the solutions for an infinite medium, the derivation of solutions for a semi-infinite medium is straightforward. We examine the spatial and temporal evolution of thermoelastic deformation for point and spherical heat sources. We applied the solution to a radar interferometric observation of post-eruptive deformation associated with the 1986 fissure eruption at Izu-Oshima volcano, Japan. Assuming a spherical heat source at a depth of 240 m with a volume of 1.15 x 107 m(3) and a temperature step 103 K, the predicted rate of post-eruptive ground movement agrees with the observed rate within observational errors. Also, the same parameter values allow us to compute the co-eruptive ground displacement by the effect of mass intrusion, whose amplitude is consistent with the observed height (45 m) of the newly formed cone. The derived solutions can be applied to transient ground displacements observed at active volcanoes, and allow us to evaluate the heat amount of magma intruded at very shallow depths.
  • 古屋 正人
    日本火山学会講演予稿集 2005 63 - 63 特定非営利活動法人 日本火山学会 2005年
  • M Furuya
    GEOPHYSICAL RESEARCH LETTERS 31 5 L5605  2004年03月 [査読有り][通常論文]
     
    Stacked radar interferograms at Miyakejima volcano ( Japan) between 1992 and 1998 showed two localized significantly deforming areas with a magnitude of 4 similar to 6 mm/yr in the radar line of sight. One area is close to the 1983 eruption vent, and, using a simple closed analytical formulation, the deformation is interpreted as due to a thermoelastic contraction of a formerly intruded magma. The other one detected in the previous caldera is explained by a depressurization source, whose depth ( 500 m) coincides with that of a low resistivity zone interpreted as a hydrothermal reservoir. Also, our computed CO2 flux is consistent with in situ measurement data. The reservoir volume is significantly less than the collapsed volume in 2000, and its depth is much shallower than the void detected prior to the collapse. Hence, the depressurization would not directly induce the caldera collapse in 2000.
  • M Furuya, S Okubo, W Sun, Y Tanaka, J Oikawa, H Watanabe, T Maekawa
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 108 B4 2219  2003年04月 [査読無し][通常論文]
     
    [1] Calderas are ubiquitous topographic features of volcanos, yet caldera formation itself has not been recorded intensively by modern measurement techniques. Here we report the spatiotemporal gravity changes before and after caldera collapse at the Miyakejima volcano, Japan in 2000. A gravity decrease of as much as 145 muGal (1 muGal = 10(-8) m/s(2)) at the summit area since June 1998 was detected 2 days prior to the collapse, interpreted as reflecting the formation of a large void beneath the volcano. Gravity changes detected after the initiation of collapse can mostly be corrected by the effect of collapsed topography, from which a rapid rate of collapse of more than 1.6 x 10(7) m(3)/d can be inferred. Correcting for the effect of topography change, we identified a temporal decrease in gravity from the middle of July to late August despite ground subsidence. The gravity decrease is interpreted as a reduction of the density in a cylindrical conduit, attributed to water inflow from an ambient aquifer that also promoted intensive magma-water interaction and subsequent explosive eruptions. From September to at least November 2000, gravity values at all sites increased significantly by a degree that cannot be explained by ground displacement alone. We interpret this temporal evolution as primarily due to magma ascent and refilling of the conduit.
  • 桜島火山における絶対重力測定（1998年〜2002年）
    京都大学防災研究所年報 46B 827 - 833 2003年 [査読無し][通常論文]
  • M Furuya, S Okubo, F Kimata, R Miyajima, Meilano, I, W Sun, Y Tanaka, T Miyazaki
    EARTH PLANETS AND SPACE 55 7 375 - 385 2003年 [査読無し][通常論文]
     
    Eruptive and caldera-forming activity at Miyakejima volcano island, Japan, commenced on 26 June 2000 was accompanied by more than 40 day of seismic swarms and significant crustal deformation in the nearby islands and sea region besides those at Miyakejima itself. The migration of the hypocenters in the early stage suggests that they were triggered by magma intrusion from Miyakejima. However, it remains uncertain whether the long-lasting seismic swarms and ground displacements in the northern Izu-islands were totally maintained by the magma flow from Miyakejima, because another magma source nearby Kozushima was suggested previously, which is 40 km north-west of Miyakejima, based upon anomalous ground displacements. Here we report the detection of associated changes with the 2000 activity in both absolute gravity and elevation at Kozushima as well as those at Miyakejima. Combining these data with horizontal GPS displacements, we extend the analysis of Nishimura et al. (2001) and construct an optimum source model, so that we can account for the observed changes in geodetic data and determine the mass budget of the magma flow. The total mass of the newly intruded dike offshore of Miyakejima and nearby Kozushima turned out to be 130% or greater than the lost mass at Miyakejima. As long as there are no other source elements, another magma reservoir near Kozushima is required and is suggested to have been activated, causing the seismic swarms and crustal deformation. We may speculate as a phenomenology that the rapid lateral magma flow from Miyakejima in the very beginning of the unrest awakened a dormant reservoir offshore of Miyakejima and Kozushima.
  • 火山 47 5 587 - 594 2002年 [査読無し][通常論文]
  • 古屋 正人, 大久保 修平, 孫 文科, 渡辺 秀文, 松本 滋夫
    日本火山学会講演予稿集 2002 113 - 113 特定非営利活動法人 日本火山学会 2002年
  • 青木 俊平, 古屋 正人, 小林 茂樹, 大久保 修平
    日本火山学会講演予稿集 2002 110 - 110 特定非営利活動法人 日本火山学会 2002年
  • 2000年有珠山噴火活動の重力測定
    北海道大学地球物理学研究報告 64 81 - 90 2001年 [査読無し][通常論文]
  • 桜島の火山活動に伴う重力変化と絶対重力測定
    月刊地球 23 8 578 - 582 2001年 [査読無し][通常論文]
  • Inland Flexure due to ocean tide loading; A possible detection by satellite radar interferometry at Korean peninsula
    CEOS SAR Workshop 2001 Proceedings 25 - 28 2001年 [査読無し][通常論文]
  • 古屋正人
    地震研究所彙報 76 237 - 246 2001年 [査読無し][通常論文]
  • 古屋 正人
    測地学会誌 47 3 701 - 710 2001年 [査読無し][通常論文]
     
    Ever since the start of polar motion observation in the late 19th century, it has remained elusive what source (s) were exciting the Chandler wobble, which is one of the Earth's free oscillatory modes. Further, the budget of excitation sources for the annual wobble has not yet been closed, either. From the middle of 1980's to 1990's, space geodetic techniques such as VLBI (Very Long Baseline Interferometry), SLR (Satellite Laser Ranging) and GPS (Global Positioning System) have matured and revolutionalized the measurement of Earth orientation parameters, providing us with order-of-magnitude higher precision data with time interval of less than a week. Meanwhile, based on an operational analysis data set of global atmosphere derived by e.g., JMA (Japan Meteorological Agency), AAM (atmospheric angular momentum) began to be routinely computed in 1990's. Using both space geodetically derived polar motion data and AAM based upon JMA's operational analysis, the author showed the importance of atmospheric wind contribution to the excitation of Chandler wobble. Also, based on an opetational analysis data set of the Pacific Ocean, the author indicated that the seasonal wobble excitation can roughly be accommodated to the atmosphere and the Pacific Ocean. On the other hand, space gravimetry mission to be launched in the beginning of the 21st century will directly unravel global-scale mass redistribution effects such as ground water and ocean bottom pressure, delivering time-dependent gravity field. Thereby, it will contribute not only to the polar motion excitation study, but also to global environmental study, providing unprecedented information for the Earth system. © 2001, The Geodetic Society of Japan. All rights reserved.
  • 重力の時空間変化でとらえた三宅島2000年火山活動におけるカルデラ形成過程
    地学雑誌 110 2 217 - 225 2001年 [査読無し][通常論文]
  • 古屋 正人, 大久保 修平, 孫 文科, 山中 佳子, 及川 純, 渡辺 秀文
    日本火山学会講演予稿集 2001 22 - 22 特定非営利活動法人 日本火山学会 2001年
  • Y Koyama, R Ichikawa, T Kondo, N Kurihara, Y Takahashi, T Yoshino, K Sebata, M Furuya
    TOWARDS AN INTEGRATED GLOBAL GEODETIC OBSERVING SYSTEM (IGGOS) 120 158 - 160 2000年 [査読無し][通常論文]
  • 新しい質量分布のリモートセンシング -次世代の重力計測とその役割-
    天気 47 1 347 - 355 2000年 [査読無し][通常論文]
  • Strain Field inferred from Keystone VLBI Network
    Proceedings of GEMSTONE workshop 265 - 270 1999年 [査読無し][通常論文]
  • Routine Observation Results of the KSP VLBI Network
    Journal of Communication Research Laboratory 46 1 159 - 164 1999年 [査読無し][通常論文]
  • M Furuya, Y Hamano
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 103 B5 10131 - 10140 1998年05月 [査読有り][通常論文]
     
    In order to assess oceanic influence on the excitation of the Earth's seasonal wobble, which is not totally explained by atmospheric angular momentum (AAM) we employed Pacific Ocean monthly analysis data from the U.S. National Center for Environmental Prediction for the period from 1980 to 1994 to compute the Pacific Ocean angular momentum (POAM) around two axes on the equatorial plane. These were chi(1), and chi(2) with respect to axis 1 and axis 2 which corresponded to motion along the Greenwich meridian and 90 degrees E, respectively. In particular, we paid attention to the chi(1) component, which was barely influenced by AAM. The variance in the AAM plus FOAM chi(1), was almost 10 times that of the AAM alone, while that of AAM plus FOAM chi(2),decreased to similar to 60% of that of AAM alone. Thus the mean seasonal cycle of FOAM plus AAM roughly accounted for the observed wobble, and its year-to-year fluctuations overlapped with those of seasonal wobble excitation. We also found that the seasonal chi(1), FOAM mostly.consisted of the motion (current) term and that the mass term played a secondary role; this is in contrast to AAM's contribution to chi(2),. Although intensive seasonal fluctuations in the chi(1), motion term were localized around the western Pacific region, we found that middle-to-higher-and lower-latitude regions were inphase and out of phase with the basin-wide contribution. However, the influence of the Pacific Ocean may be reduced by other unaccounted for sources such as effects from other oceanic basins and land water.
  • T Kondo, N Kurihara, A Koyama, M Sekido, R Ichikawa, T Yoshino, J Amagai, K Sebata, M Furuya, Y Takahashi, H Kiuchi, A Kaneko
    GEOPHYSICAL RESEARCH LETTERS 25 7 1047 - 1050 1998年04月 [査読無し][通常論文]
     
    Since 1995, VLBI measurements using fixed VLBI stations around the Tokyo metropolitan area have been continually producing data of station positions and baseline lengths. The accuracy of baseline length measurements is evaluated in terms of repeatability, conventionally defined as a standard deviation of those obtained by five continuous sessions. Continuous improvement both in system hardware and in the observation method have resulted in a remarkable improvement in measurement accuracy. Repeatability reaches about a 2-mm level in baseline length in our VLBI network.
  • M Furuya, Y Hamano, Naito, I
    JOURNAL OF PHYSICS OF THE EARTH 45 3 177 - 188 1997年 [査読無し][通常論文]
     
    We explored the atmospheric contribution to the excitation of Chandler wobble (CW), which has spanned about 11 years beginning from September 1983. The atmospheric angular momentum (AAM) function presented by the Japan Meteorological Agency (JMA) and the wobble data set (SPACE93) are employed. We devised a wobble domain method of analysis which enables us to quantify the narrow band power of AAM. The AAM-induced wobble closely resembles the observed wobble, and wind contribution turns out to dominate over atmospheric pressure contribution in the vicinity of the Chandler frequency. When only pressure contribution is taken into account, it is insufficient, as shown in previous studies.
  • M Furuya, BF Chao
    GEOPHYSICAL JOURNAL INTERNATIONAL 127 3 693 - 702 1996年12月 [査読無し][通常論文]
     
    The period P and Q-value of the Chandler wobble are two fundamental functionals of the Earth's internal physical properties and global geodynamics. We revisit the problem of the estimation of P and Q, using 10.8 yr of modern polar motion as well as contemporary atmospheric angular momentum (AAM) data. We make full use of the knowledge that AAM is a major broad-band excitation source for the polar motion. We devise two optimization criteria under the assumption that, after removal of coherent seasonal and long-period signals, the non-AAM excitation is uncorrelated with the AAM. The procedures lead to optimal estimates for P and Q. Our best estimates, judging from comprehensive sets of Monte Carlo simulations, are P = 433.7 +/- 1.8 (1 sigma) days, Q = 49 with a 1 sigma range of (35, 100). In the process we also obtain (as a by-product) an estimate of roughly 0.8 for a 'mixing ratio' of the inverted-barometer (IB) effect in the AAM pressure term, indicating that the ocean behaves nearly as IB in polar motion excitation on temporal scales from months to years
  • M Furuya, Y Hamano, Naito, I
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 101 B11 25537 - 25546 1996年11月 [査読有り][通常論文]
     
    The atmospheric contribution to the excitation of the Chandler wobble (CW) is studied for a period of about 11 years period beginning in September 1983, using the wobble data set (SPACE93). Two atmospheric angular momentum (AAM) functions are employed; one is based on Japan Meteorological Agency (JMA) data, and the other is based on U.S. National Meteorological Center (NMC) data. In the vicinity of the Chandler frequency, the excitation power for both AAM functions is comparable with that inferred from the observed wobble. If we separate the AAM excitation into wind and pressure effects, the wind contribution exceeds the pressure contribution around the Chandler frequency. In addition, the JMA wind AAM function reveals a spectral peak around the Chandler frequency. Significant coherence with the inferred excitation exceeding the 99% confidence level can be recognized for both JMA and NMC wind excitation. We propose that the wind contribution to the excitation of polar motion may be somewhat larger than at other frequencies because of the existence of quasi-periodic atmospheric variations that have been found in other investigations. In a narrow-band analysis of the excitation using least squares fit sinusoids, we found that both the amplitude and phase of the inferred excitation near the Chandler band indicate their strong dependence on the assumed Chandler period and that an assumed CW period of 431 days caused atmospheric and observed excitations to agree most closely.

書籍

  • リモートセンシング事典
    古屋正人 (担当:分担執筆範囲:7-11 氷河の流動と変動)
    日本リモートセンシング学会 2022年12月 (ISBN: 9784621307762)
  • 図説地球科学の事典
    古屋 正人 (担当:分担執筆範囲:5.7 地球回転)
    朝倉書店 2018年04月
  • 地形の辞典
    古屋 正人 (担当:分担執筆)
    朝倉書店 2017年02月
  • 地球惑星科学入門、第1章
    古屋 正人 (担当:分担執筆)
    北海道大学出版会 2010年
  • マグマダイナミクスと火山噴火
    古屋 正人 (担当:分担執筆)
    朝倉書店 2002年

その他活動・業績

受賞

  • 2021年05月 日本火山学会 日本火山学会論文賞
     Precursory ground deformation of the 2018 phreatic eruption on Iwo-Yama volcano, revealed by four-dimensional joint analysis of airborne and spaceborne InSAR, Earth Planets Space, 72, 1, doi:10.1186/ s40623-020-01280-5. 
    受賞者: 成田翔平;小澤拓;青木陽介;島田政信;古屋正人;高田陽一郎;村上亮
  • 2010年 エスペック環境研究奨励賞
  • 2010年 ESPEC Prize for the Encouragement of Environmental Studies
  • 2007年 Guy Bomford Prize
  • 2004年 日本火山学会論文賞
  • 2004年 Best paper award
  • 2000年 日本測地学会坪井賞
  • 2000年 The Tsuboi Prize of the Geodetic Society of Japan

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    研究期間 : 2023年04月 -2028年03月 
    代表者 : 古屋 正人, 石川守, 岩花剛, 柳谷一輝
  • 日本学術振興会：科学研究費助成事業 基盤研究(A)
    研究期間 : 2020年04月 -2025年03月 
    代表者 : 杉山 慎, 菅 浩伸, 古屋 正人, 青木 茂
     
    前年度に引き続き、2021年度もCOVID-19の影響を受けて、チリおよびアルゼンチンでの氷河観測が実施できない状況となった。そこで当初の計画を一部変更して、南極における野外観測を実施すると共に、人工衛星データを使った解析に力を入れた。その結果、南極のカービング氷河における重要な観測データが得られた他、既存のデータと衛星データの解析で論文出版と学会発表の成果が挙がった。 (1) 野外観測： 2021年12月から2022年1月にかけて、南極ラングホブデ氷河で熱水掘削を含む観測を実施して、カービング氷河の底面観測に成功した。当初計画とは異なる地域、異なる手法による観測であるが、氷河氷床と海洋の相互作用解明につながる重要なデータが得られたと考えている。このほか、パタゴニアでの氷河・氷河湖・海洋調査に向けて、観測機器の調査と準備を行った。特にマルチビームソナーを使った観測に関して、専門業者への観測委託の検討が進んだ。 (2) データ解析： 過去にチリ・グレイ氷河の前縁湖で測定した水温と流速データを解析して、氷河排水が氷河湖の水温季節変動に与える影響を明らかにした。また人工衛星データの解析によって、パタゴニア西部グレーベ湖で2020年に起きた急激な水位低下を発見した。詳しい解析の結果、この現象が近年では世界最大の氷河湖排水イベントであることが判明した。 (3) 論文出版・学会発表：グレイ湖で測定した通年の水温変化をNature Communications誌に出版した他、氷河湖排水イベントをCommunications Earth & Environment誌に投稿中。COVID-19の影響で海外における学会発表は困難となり、国内での学会で成果を発表した。 (4) 研究会合：10月にオスロ大学の研究者とオンラインでワークショップを開催した他、研究チームでの小規模な会合を適宜開催した。
  • 永久凍土地帯における森林火災後の地盤変動:時空間変化の検出とモデリング
    文部科学省：科学研究費補助金 基盤研究(C)(一般)
    研究期間 : 2019年04月 -2022年03月 
    代表者 : 古屋 正人
  • 文部科学省：科学研究費補助金（新学術領域研究（研究領域提案型）)：科学研究費助成事業
    研究期間 : 2018年04月 -2020年03月 
    代表者 : 古屋 正人
     
    【課題A】集中豪雨/雷雲へのInSAR Split-Spectrum-Method(SSM)の適用と位相モデルの検討 今年度はALOS2によるInSARで5つの豪雨事例に伴う水蒸気分布を捉えた：鹿児島県(2018年7月3日)、高知県(2018年8月15日)、兵庫県(2018年6月29日)、大阪府(2018年5月13日)、近畿地方での台風21号Jebi(2018年9月4日)．鹿児島県、高知県のデータからは降雨レーダーの降水分布に対応した顕著な水蒸気分布の異常が見出された．Split-Spectrum-Method(SSM)を適用した結果もほぼ非分散性位相に起因しているが，前年度に報告した事例と同様，分散性成分の方にも豪雨発生域に異常位相が有意に残っており、降水粒子を検出している可能性がある． 【課題B】電離層擾乱へのInSAR SSM の適用 ALOS2のScanSARモード画像を用いて広域の電離層擾乱の検出を試みた．スポラディックE（Es）は日本域では夏の昼間の発生頻度が高く，ALOS2 ScanSARの撮像時刻がマッチせずInSARで検出できるには至らなかったが，伝搬性の電離層擾乱は明確に捉えられた． ALOS1データを用いて、新たに広島/岡山付近のEsイベント(2010年6月26日)を検出した．SSMを用いた電離層起源の分散性位相とそれ以外の非分散性位相に概ね分離できるが，分離前には異常が見られない箇所で分散性/非分散性位相のそれぞれに新たに異常が現れ、しかも分散性/非分散性位相で打ち消し合う結果が見られた．Es発生時以外では同様のシグナルが見られないこと、これまでのEs検出例でも同様の事例があることから，Es時に特有の「現象」である可能性がある．
  • 東シベリア平原の森林火災に伴う地盤変動の時空間変化の検出とモデリング
    北極域研究共同研究拠点研究者コミュニティー推進事業：共同推進研究
    研究期間 : 2018年04月 -2019年03月 
    代表者 : 古屋 正人
  • 電離層補正を考慮したInSARによる永久凍土域の地盤変動検出
    北極域研究共同研究拠点研究者コミュニティー推進事業：共同推進研究
    研究期間 : 2017年04月 -2018年03月 
    代表者 : 古屋 正人
  • 北極域研究共同研究拠点研究者コミュニティー推進事業：共同推進研究
    研究期間 : 2016年04月 -2017年03月 
    代表者 : 古屋 正人
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2011年04月 -2015年03月 
    代表者 : 杉山 慎, 澤柿 教伸, 内藤 望, 古屋 正人, 榎本 浩之
     
    本研究では、人工衛星データの解析と現地観測によって、パタゴニアと南極半島におけるカービング氷河の変動とそのメカニズム解明に取り組んだ。その結果、南パタゴニア氷原における1984年以降の氷河変動を定量化し、近年の氷河後退と流動変化の関係を明らかにした。また氷河湖の底面地形と水塊構造を測定し、湖が氷河変動に果たす役割を示した。さらに南極半島のカービング氷河を熱水掘削することによって、氷河底面の水理環境と氷河流動の関係を明らかにした。以上の成果は、特に研究の進んでいないパタゴニア・南極半島地域におけるカービング氷河の変動と、そのメカニズムの理解を推し進めるものである。
  • 文部科学省：科学研究費補助金(挑戦的萌芽研究)
    研究期間 : 2012年04月 -2015年03月 
    代表者 : 古屋 正人
     
    「氷河サージ」とは氷河の流速が平時に比べ数10倍以上も上昇して末端が前進する現象である．しかし数10年以上の静穏期を経て発生する稀な現象でデータが乏しく，発生機構は氷河学上の未解決問題の一つである．ここでは人工衛星搭載の合成開口レーダー(SAR)データを利用し，氷河の表面流動速度の時空間的変化を調べ，発生機構の解明を目指した．成果の一つは，西クンルン山脈での氷河サージの発見で，５年以上継続しつつも秋から冬にかけての加速する季節的変調を初めて検出した．またカナダユーコン域の静穏期のサージ型氷河でも冬期加速を発見した．表面融解しない時期でも加速する事実は，氷体内部での融解水の滞留と移動を示唆する．
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2009年 -2011年 
    代表者 : 及川 純, 古屋 正人, 井口 正人, 青木 陽介, 綿田 辰吾
     
    干渉合成開口レーダー(InSAR)は様々な地殻変動の解析に用いられている.特に面的な地殻変動を捉えるには最も有効な手法である.本研究では,国内で最も活発な火山の一つである諏訪之瀬島において,InSARを用いて地殻変動を観測したが,火山活動が活発だったにも関わらず明瞭な地殻変動は無かった.諏訪之瀬島に代表されるような開口系火道を持つマグマ供給システムの性質ではないかと考えられるが,これを実証する為にも,さらに精度のよい観測研究を行う必要がある.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2008年 -2010年 
    代表者 : 日置 幸介, 古屋 正人
     
    2010年2月のチリ地震に伴う重力変化をGRACE衛星データから検出した(Heki & Matsuo,2010 GRL)。これはスマトラ地震に続き世界二例目である。また地球温暖化に伴うアジア高山域(特にヒマラヤ山脈)の年間40Gtに及ぶ山岳氷河の縮小をGRACE衛星データから定量的に求めた(Matsuo & Heki,2010 EPSL)。しばしばGRACEデータに現れる重力変化の加減速の原因が降水量の直線変化であることを突き止めた(Ogawa et al.,2011 GJI)。
  • 文部科学省：科学研究費補助金(基盤研究(B))
    研究期間 : 2007年 -2009年 
    代表者 : 古屋 正人, 高田 陽一郎
     
    陸域プレート境界やその周辺で発生した国内外の内陸地震に伴う地殻変動を,合成開口レーダー(SAR)で検出した.いずれの事例でも速報的に得られる震源情報からは予想出来ない意外な地殻変動シグナルが得られ,SARが無ければ見逃されていたであろう.アフガニスタンのチャマン断層では,マグニチュード5の地震の後に1年以上も余効滑りが続いた.1996年鬼首,2007年中越沖,2008年岩手宮城内陸,2008年于田(チベット),2008年〓川(四川省)のいずれの地震でも,一枚の矩形断層で滑り分布を考慮しても説明できない複雑な地殻変動が検出された.複数枚の断層面,傾きや走向の変化,面自体の屈曲といった形状の複雑性が内陸地震では普遍的に存在する可能性が示された.鬼首地震と中越沖地震では本震断層とは離れたところにも顕著な変動シグナルを検出し,非地震性の断層運動で説明した.
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2008年 -2008年 
    代表者 : 小長井 一男, 千木良 雅弘, 塩原 等, 平田 直, 桑原 保人, 古屋 正人, 孫 文科, 池田 安隆, 渥美 公秀, 釜井 俊孝, 福岡 浩, 汪 発武, 高橋 良和, 大町 達夫, 川島 一彦, 河野 進, 壁谷澤 寿海, 中埜 良昭, 宮澤 理稔, 飛田 幹男, 島田 政信, 狩野 謙一, 林 為人, 多々納 裕一, 矢守 克也, 梶谷 義雄, 塩原 等
     
    2008年5月12日に中国四川省汶川県付近を震源とするマグニチュード(M)7.9(米国地質調査所)の内陸巨大地震が発生し、死者7万人、行方不明者2万人に達すると推定される甚大な被害がもたらされた。この地震を引き起こした断層の長さは280km程度と推定され、内陸部で発生した地震としては最大級の地震である。我が国の内陸部でも、これまでに、M8級の巨大地震として1891年濃尾地震が発生し、7200名余の死者を出し、今後もM8級の地震が発生する可能性が指摘されている(糸魚川―静岡構造線断層帯、富士川河口断層帯や中央構造線断層帯など)。しかし、近年発生した最大規模の被害地震は平成7年兵庫県南部地震(阪神・淡路大震災)で、M7.3、断層の長さ50km程度であり、M8級の巨大地震の発生機構は十分に明らかにされていない。また今回の地震では断層沿いの山地に大量の不安定な土石が残されていて、下流域にとって土石流などの深刻な不安材料となっている。強烈な揺れへの対応とあわせ、長期に及ぶ復興の課題に資する科学的調査もまた重要である。このような理学・工学そして社会対応に至るまであらゆる局面から本地震の実態と、その影響を科学的に検証していくことは、我が国の内陸における巨大地震の発生機構の解明に資するのみならず、地震災害の軽減、そして合理的な復興戦略策定に資するデータを提供することに繋がり、我が国の防災戦略に役立つ。このような観点で中国地震局を正式なカウンターパートとしての共同調査を行った。主要な調査対象は(1) 斜面災害、(2) 社会基盤施設被害、(3) 建築・家屋被害、(4)地震学的分野、(5) 地殻変動、(6) 活断層、(7) 救援・復旧支援活動及び経済的影響、の7領域に及ぶ。これらの調査の中で、「だいち」(JAXA)「だいち」の緊急観測やALOS衛星画像の解析などで中国側に重要な情報を提供できた。このなかにはInSAR画像の解析や、5万㎡以上の面積の斜面崩壊分布を明らかにしたことなどが挙げられる. また, 現地調査でも衛星で確認された崩壊地で白雲岩などの炭酸塩岩に最も多くの崩壊が発生していることや、崩壊の方向に指向性があることなどを見出した. さらに社会基盤施設や建築物・家屋の崩壊について個別の調査を行い、それぞれを詳細なレポートとしてまとめている。一方で、現地は物理的にも立ち入り困難な場所があり、その被害の全貌を把握することは単年度の本研究の枠を超えて進めるべき課題で、今後の相互の学術発展のみならず有効な復旧戦略構築のためにも日中の協力の枠組みを強化することがいよいよ重要である。
  • 文部科学省：科学研究費補助金(若手研究(B))
    研究期間 : 2002年 -2003年 
    代表者 : 古屋 正人
     
    今年度は(1)1996年8月に宮城秋田山形県境付近で発生した「鬼首地震」による地震時地殻変動、(2)伊豆大島火山のカルデラ域における経年的沈降の「微細構造」の検出に成功した。以下にそれぞれの概略を述べる。(1)1996年8月11日に宮城秋田山形県境付近の鬼首地域でM5.9の地震が発生した。地震そのものの規模は大きくないが震源深さが10kmよりも浅かったために,現存するGPS等の宇宙技術によって検出可能な地表変位が現れた。しかしM5.9の中規模の地震による地表変位は水平距離で10km程度にしか及ばず,山間部での地震であったためGPS受信機の空間分布は疎らなため断層モデルを推定できるほどの空間分解能では検出できていなかった。今回JERS1(ふよう1号)のデータを用いて干渉SAR解析を行い,独立な3ペアにつき地震時地殻変動を検出できた。その結果は余震分布で推定された断層モデルで概ね説明できるが,空間的な広がりの点で地震学的には説明できない変位が得られている。(2)伊豆大島カルデラにあっては,JERS1データの干渉SARによって経年的な沈降が報告されている。この事実に基づき「多重干渉SARによる経年性地殻変動検出」のテストフィールドとして伊豆大島カルデラを選び、ERS1/2による干渉SAR解析を行った。ERS1/2のデータを用いたことによって、沈降の微細構造が判明した。沈降域と過去の...
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2001年 -2003年 
    代表者 : 孫 文科, 古屋 正人, 大久保 修平
     
    主に理論的な研究を行った:1.半無限体と均質球、そして均質球と成層構造球に対する計算された結果の比べによって、それぞれ曲率と成層構造の影響が定量的に得られました。この影響が非常に大きいことが分かりました。2.孫と大久保の球体Dislocation理論の数学的に複雑な弱点を乗り越えるために、球体地球に関するAsymptotic Dislocation理論を提出しました。この理論が曲率と成層構造の影響を含むので物理的に合理です。同時にこの理論が解析で表されるので数学的にも簡単です。3.2000年三宅島火山噴火による地殻変形をDislocation理論で研究しました。4.重力衛星によるCo-seismicジオイドと重力変化を検出できるかという問題も調べた。この研究には、重力衛星の空間解析度を考え、空間で観測できるco-seismic変形を研究し、切断変形の理論研究と数値計算を行った。5.地震によって生じる歪の計算式を導きました。これらの研究成果を日本地学関連合同大会2002、測地学会、WPGM2002年会、そして、2003年IUGG総会(札幌)などで発表しました。同時に、これらの成果を8篇の論文にまとめてJournal of Geophysical Research、Geophysical Research Letterなど雑誌に発表されました。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 2001年 -2003年 
    代表者 : 大久保 修平, 孫 文科, 古屋 正人, 日比谷 紀之
     
    マックスウェル粘弾性体中で起きる断層運動によって生じる重力変化・上下変位を計算する理論を完成するとともに計算コード化をすすめた。15年度には,プレート沈み込みにともなう重力および上下変位の経年変化(インターサイスミックな変化)が計算できるようになった。具体的には、プレート境界上に適切なアスペリティ分布を仮定して、それにSavageのバックスリップモデルを適用することにより、地震が繰り返す間の期間(インターサイスミック・ピリオド)における、上下変位と重力変化の時間的な推移を見積もった。この手法をフィリピン海プレートが日本列島下にもぐりこんでいる東海地方に適用した。その結果、定常的な沈降量(たとえば御前崎では年間7mm程度の沈降)は、ごく普通の粘性構造分布とアスペリティの分布を仮定すれば、上記モデルで説明可能であることが示された。一方、重力変動の方は、同じモデルでは観測量よりも有意に大きな変動((年間1.5マイクロガルの重力増)が計算された。これは、重力変動が累積しないというSavageの理論に根本的な疑問を投げかける重要な成果といえる。また、同じ計算手法を、2003年9月の十勝沖地震にともなう、重力変動の解析にも適用した。このばあいには、地震の5年前に観測されていた絶対重力データに、観測時から地震直前までに生じたであろう重力変化を加えることにより、地震直前の絶対重力値を求めることに成功した。この値を、2003年10月に実施した絶対重力観測値と比較することにより、コサイスミックな重力変動を見積もることができた。
  • 日本学術振興会：科学研究費助成事業
    研究期間 : 1998年 -2000年 
    代表者 : 大久保 修平, 古屋 正人, 日比谷 紀之
     
    1.干渉合成開口レーダー解析による地殻変動の解析にとって,最大の誤差要因となる水蒸気遅延について,それを気象庁領域客観解析データを用いて取り除く手法の開発を進めた.開発手法の有効性を確認するために,海洋潮汐荷重による地表変位が大きいと見積もられている朝鮮半島について干渉合成開口レーダー解析を完了した.得られた地殻変動の空間的なパターンは,解析結果と予測値とが良い一致を示したが,振幅は理論的な予測値と比べて2倍程度の大きさとなった.海洋潮汐モデルもしくは荷重グリーン関数に問題が残っていると考えられる. 2.巨大地震によって励起される地殻変動の時間的推移を求めるために,マックスウェル粘弾性地球内におかれた点震源について,自己重力および圧縮性を考慮にいれた球対称モデルに基づき,重力・ジオイド高・上下変動を計算する手法を完成した.垂直断層上の水平横ずれ断層型の場合に実際に計算を行なった結果,弾性リソスフェア内に震源がある場合と,粘弾性アセノスフェアにある場合とで,変形の時間的な推移が大きく異なることがわかった. 3.グローバルな内部潮汐波場の数値モデリングを行うため,北太平洋におけるM2成分の内部潮汐の分布を,プリミティブ運動方程式の3次元数値モデルを利用して調べた.その結果,大振幅の内部潮汐が,インドネシア諸島・ソロモン諸島・アリューシャン諸島の海山,東シナ海の大陸棚斜面,伊豆・小笠原海嶺やハワイ海嶺といった卓越した海底地形上において励起されている様子が再現された.とくに,ハワイ海嶺付近のM2内部潮汐の空間分布について,この数値計算によって再現されたものと,Topex/Poseidonの海面高度計データから検出されたものとがよく一致していることが確認された.
  • 主として測地学による地球惑星ダイナミクスの観測的理論的研究
    研究期間 : 1997年

教育活動情報

主要な担当授業

  • 遠隔情報学特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 環境科学院
    キーワード : リモートセンシング，人工衛星，遠隔探査 remote sensing
  • 地殻ダイナミクス特論
    開講年度 : 2021年
    課程区分 : 修士課程
    開講学部 : 理学院
    キーワード : 宇宙測地学、地球回転、極運動、ウォブル、自転角速度変動、地心座標系
  • 地球惑星科学実験Ⅳ
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 岩石学, 火山学, 地球化学, 火山岩, マグマ，全球衛星測位システム, GEONET, 合成開口レーダー, 合成開口レーダー干渉法, データ処理
  • 一般教育演習(ﾌﾚｯｼｭﾏﾝｾﾐﾅｰ)
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 有珠山、地殻変動、合成開口レーダ、SAR、宇宙測地学、人工衛星、Linux
  • 宇宙測地学
    開講年度 : 2021年
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 人工衛星,全地球測位システム,超長基線電波干渉法,衛星レーザー測距,衛星高度計,干渉合成開口レーダー,衛星間測距,座標系,地球回転,プレート運動,地殻変動,重力,ジオイド,リモートセンシング，最小二乗法

大学運営

委員歴

  • 2023年10月 - 2029年09月   日本学術会議 第26,27期   連携会員
  • 2023年07月 - 2027年07月   国際測地学協会 執行委員会   Member-At-Large
  • 2023年10月 - 2024年03月   Progress in Earth and Planetary Science   ジャーナル編集委員
  • 2017年10月 - 2023年09月   日本学術会議 第24,25期   連携会員
  • 2017年10月 - 2023年09月   日本学術会議地球惑星科学委員会IUGG分科会IAG小委員会   委員長
  • 2021年03月 - 2021年06月   European Space Agency, Fringe 2021 Workshop   Science Committee Member
  • 2016年07月 - 2020年12月   Earth Planets Space   Vice Editor-in-chief
  • 2016年05月 - 2018年03月   IAG-IASPEI2017   LOC member
  • 2016年11月 - 2017年06月   European Space Agency, Fringe 2017 workshop   Scientific Committee
  • 2007年08月 - 2015年06月   Journal of Geodesy   Editorial board member
  • 2014年06月 - 2015年03月   European Space Agency, Fringe 2015 workshop   Scientific Committee
  • 2011年02月 - 2011年09月   European Space Agency, Fringe 2011 workshop   Scientifc Comittee
  • 2006年 - 2010年   日本火山学会   編集委員   日本火山学会
  • 2010年   日本測地学会   評議員   日本測地学会
  • 2007年 - 2008年   日本測地学会   評議員   日本測地学会
  • 2008年   日本地球惑星科学連合   代議員   日本地球惑星科学連合
  • 2007年   日本測地学会   編集委員   日本測地学会

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