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Masato Furuya
Faculty of Science　Earth and Planetary Sciences　Earth and Planetary Dynamics
Professor
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Last Updated :2024/05/09

Researcher Profile and Settings

Affiliation

  • Faculty of Science　Earth and Planetary Sciences　Earth and Planetary Dynamics

Job Title

  • Professor

Degree

  • PhD（The University of Tokyo）

URL

Research funding number

  • 60313045

ORCID ID

Researcher ID

  • E-1296-2011

J-Global ID

Research Interests

  • Extreme weather   gravity   volcano   earthquake   InSAR   permafrost   ionosphere   glacier   Earth rotation   crustal deformation   SAR   Space geodesy   

Research Areas

  • Natural sciences / Space and planetary science
  • Environmental science/Agricultural science / Environmental dynamics
  • Natural sciences / Atmospheric and hydrospheric science
  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Disaster prevention engineering
  • Natural sciences / Solid earth science

Educational Organization

Academic & Professional Experience

  • 2012/01 - Today Hokkaido University, Faculty of Science Department of Earth and Planetary Sciences
  • 2007/10 - 2011/12 Hokkaido University, Faculty of Science Department of Earth and Planetary Sciences
  • 1999/04 - 2007/09 The University of Tokyo Earthquake Research Institute
  • 2003/08 - 2005/07 University of Colorado at Boulder Department of Physics
  • 1997/04 - 1999/03 Communications Research Laboratory, MPT

Education

  •        - 1997  The University of Tokyo
  •        - 1997  The University of Tokyo  Graduate School, Division of Science
  •        - 1992  The University of Tokyo  Faculty of Science
  •        - 1992  The University of Tokyo  Faculty of Science

Association Memberships

  • THE JAPANESE SOCIETY OF SNOW AND ICE   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   

Research Activities

Published Papers

  • Ryuji Yamaguchi, Masato Furuya
    Earth, Planets and Space 76 (1) 2024/01/02 [Refereed]
     
    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) 1343-8832 2023/12
  • K. Yanagiya, M. Furuya, P. Danilov, G. Iwahana
    Journal of Geophysical Research: Earth Surface 128 (2) 2169-9003 2023/02/12 [Refereed]
  • Masato Furuya, Fumiko Matsumoto
    Geophysical Research Letters 49 (1) 0094-8276 2021/12/29 [Refereed]
  • Yosuke Aoki, Masato Furuya, Francesco De Zan, Marie Pierre Doin, Michael Eineder, Masato Ohki, Tim J. Wright
    Earth, Planets and Space 73 (1) 1343-8832 2021/12
  • Naufal Setiawan, Masato Furuya
    Earth, Planets and Space 73 (1) 2021/07 [Refereed][Not invited]
     
    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 1873-9652 2021/03 [Refereed][Not invited]
     
    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) 1343-8832 2020/10 [Refereed][Not invited]
     
    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) 2333-5084 2020/10 [Refereed][Not invited]
  • Yuji Himematsu, Masato Furuya
    Tectonophysics 791 228571 - 228571 0040-1951 2020/09 [Refereed][Not invited]
  • Kazuki Yanagiya, Masato Furuya
    Journal of Geophysical Research: Earth Surface 2020/06/09 [Refereed][Not invited]
  • Yuji Himematsu, Freysteinn Sigmundsson, Masato Furuya
    Journal of Geophysical Research: Solid Earth 124 (9) 9940 - 9955 2169-9313 2019/09 [Refereed][Not invited]
     
    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 0022-1430 2018/06/01 [Refereed][Not invited]
     
    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 [Refereed][Not invited]
  • Masato Furuya, Takato Suzuki, Jun Maeda, Kosuke Heki
    Earth, Planets and Space 69 175  1880-5981 2017/12 [Refereed][Not invited]
     
    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
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research 公益社団法人 日本雪氷学会／日本雪工学会 2017 186 - 186 2017
  • Hata Shuntaro, Furuya Masato
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research 公益社団法人 日本雪氷学会／日本雪工学会 2017 187 - 187 2017
  • FUKUI Kotaro, FUJITA Koji, TSHERING Phuntsho, FURUYA Masato
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research 公益社団法人 日本雪氷学会／日本雪工学会 2017 89 - 89 2017
  • Youhei Kinoshita, Masato Furuya
    Sola 13 (0) 79 - 84 1349-6476 2017 [Refereed][Not invited]
     
    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 [Refereed][Not invited]
  • Yuji Himematsu, Masato Furuya
    Earth, Planets and Space 68 (1) 1343-8832 2016/12/01 [Refereed][Not invited]
     
    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.
  • ABE Takahiro, FURUYA Masato
    Seppyo 日本雪氷学会 78 (6) 425 - 438 0373-1006 2016/11 [Refereed][Not invited]
  • Himematsu, Y., Furuya, M.
    Earth Planets and Space 68 169  1880-5981 2016 [Refereed][Not invited]
     
    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 0094-8276 2016 [Refereed][Not invited]
     
    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 1994-0416 2016 [Refereed][Not invited]
     
    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 2015/11 [Refereed][Not invited]
  • Yuji Himematsu, Masato Furuya
    Tectonophysics 656 52 - 60 0040-1951 2015/08 [Refereed][Not invited]
     
    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.
  • Abe Takahiro, Furuya Masato, Sakakibara Daiki
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research 公益社団法人 日本雪氷学会／日本雪工学会 2015 7 - 7 2015
  • Abe Takahiro, Furuya Masato
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research 公益社団法人 日本雪氷学会／日本雪工学会 2015 8 - 8 2015
  • Yasuda, Takatoshi, Furuya, Masato
    Journal of Geophysical Research-Earth Surface 120 (11) 2393 - 2405 2169-9003 2015 [Refereed][Not invited]
     
    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 1880-5981 2015 [Refereed][Not invited]
     
    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 1994-0416 2015 [Refereed][Not invited]
     
    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 2014/05 [Refereed][Not invited]
  • Youhei Kinoshita, Masanobu Shimada, Masato Furuya
    Geophysical Research Letters 40 (17) 4740 - 4744 0094-8276 2013/09/06 [Refereed][Not invited]
     
    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 0949-7714 2013 [Refereed][Not invited]
     
    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 0037-1106 2013 [Refereed][Not invited]
     
    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 0034-4257 2013 [Refereed][Not invited]
     
    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 [Refereed][Not invited]
     
    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.
  • Fialko, Y., Furuya, M., Kaneko, Y., Sandwell, D. T., Tong, X.
    Journal of Geophysical Research-Solid Earth American Geophysical Union 118 (1) 316 - 331 0148-0227 2013 [Refereed][Not invited]
     
    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 0034-4257 2013 [Refereed][Not invited]
     
    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 0956-540X 2012/01/09 [Refereed][Not invited]
     
    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.
  • ABE TAKAHIRO, FURUYA MASATO
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research 公益社団法人 日本雪氷学会／日本雪工学会 2012 5 - 5 2012
  • Yasuda Takatoshi, Furuya Masato
    Summaries of JSSI and JSSE Joint Conference on Snow and Ice Research 公益社団法人 日本雪氷学会／日本雪工学会 2012 2 - 2 2012
  • TAKADA Youichiro, KOBAYASHI Tomokazu, FURUYA Masato, MURAKAMI Makoto
    Journal of the Geodetic Society of Japan The Geodetic Society of Japan 57 (4) 181 - 193 0038-0830 2011 [Refereed][Not invited]
     
    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 0040-1951 2011 [Refereed][Not invited]
     
    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.
  • Murakami Makoto, Okuyama Satoshi, Furuya Masato, Abe Takahiro
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2011 55 - 55 2011
  • 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 1880-5981 2010 [Refereed][Not invited]
     
    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 0037-1106 2010 [Refereed][Not invited]
     
    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 0939-9585 2010 [Refereed][Not invited]
     
    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 0949-7714 2010 [Refereed][Not invited]
     
    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 0012-821X 2010 [Refereed][Not invited]
     
    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 1880-5981 2010 [Refereed][Not invited]
     
    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 0094-8276 2009/04 [Refereed][Not invited]
     
    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 1343-8832 2009 [Refereed][Not invited]
     
    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 1343-8832 2008 [Refereed][Not invited]
  • Furuya, M., Satyabala, S. P.
    Geophysical Research Letters 35 (6) L06309  0094-8276 2008 [Refereed][Not invited]
     
    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 0096-3941 2008 [Not refereed]
  • Oikawa Jun, Aoki Yosuke, Furuya Masato, Iguchi Masato
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2008 73 - 73 2008
  • Yosuke Aoki, Masato Furuya, Teruyuki Kato
    Earth, Planets and Space 60 (11) 1075 - 1080 1880-5981 2008 [Refereed][Not invited]
     
    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 [Not refereed][Not invited]
  • Furuya, M., Mueller, K., Wahr, J.
    Journal of Geophysical Research-Solid Earth 112 (B6) B06418  0148-0227 2007 [Refereed][Not invited]
     
    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.
  • Masato Furuya
    Journal of Geodetic Society of Japan The Geodetic Society of Japan 52 (4) 225 - 243 0038-0830 2006 [Refereed][Not invited]
     
    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.
    Proc. Workshop : Forcing of polar motion in the Chandler frequency band : a contribution to understanding interannual climate variations, Cahiers du Centre Europeen de Geodynamique et de Seismologie, Walferdange, Luxembourg, 2005 24 57 - 59 2005 [Refereed][Not invited]
  • Furuya, M., Wahr, J. M.
    Geophysical Research Letters 32 (14) L14501  0094-8276 2005 [Refereed][Not invited]
     
    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 0956-540X 2005 [Refereed][Not invited]
     
    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.
  • Furuya Masato
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2005 63 - 63 2005
  • M Furuya
    GEOPHYSICAL RESEARCH LETTERS 31 (5) L5605  0094-8276 2004/03 [Refereed][Not invited]
     
    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  2169-9313 2003/04 [Not refereed][Not invited]
     
    [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 [Not refereed][Not invited]
  • M Furuya, S Okubo, F Kimata, R Miyajima, Meilano, I, W Sun, Y Tanaka, T Miyazaki
    EARTH PLANETS AND SPACE 55 (7) 375 - 385 1343-8832 2003 [Not refereed][Not invited]
     
    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 [Not refereed][Not invited]
  • Furuya M., Okubo S., Sun W., Watanabe H., Matsumoto S.
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2002 113 - 113 2002
  • AOKI Shumpei, FURUYA Masato, KOBAYASHI Shigeki, OKUBO Shuhei
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2002 110 - 110 2002
  • 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 [Not refereed][Not invited]
  • 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 [Not refereed][Not invited]
  • 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 [Not refereed][Not invited]
  • 古屋正人
    地震研究所彙報 76 237 - 246 2001 [Not refereed][Not invited]
  • Masato Furuya
    journal of the geodetic society of japan 47 (3) 701 - 710 0038-0830 2001 [Not refereed][Not invited]
     
    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 [Not refereed][Not invited]
  • Furuya M., Okubo S., Sun W., Yamanaka Y., Oikawa J., Watanabe H.
    PROGRAMME AND ABSTRACTS THE VOLCANOLOGICAL SOCIETY OF JAPAN 特定非営利活動法人 日本火山学会 2001 22 - 22 2001
  • 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 0939-9585 2000 [Not refereed][Not invited]
  • 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 [Not refereed][Not invited]
  • Strain Field inferred from Keystone VLBI Network
    Proceedings of GEMSTONE workshop 265 - 270 1999 [Not refereed][Not invited]
  • Routine Observation Results of the KSP VLBI Network
    Journal of Communication Research Laboratory 46 (1) 159 - 164 1999 [Not refereed][Not invited]
  • M Furuya, Y Hamano
    JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH 103 (B5) 10131 - 10140 2169-9313 1998/05 [Refereed][Not invited]
     
    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 0094-8276 1998/04 [Not refereed][Not invited]
     
    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 0022-3743 1997 [Not refereed][Not invited]
     
    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 0956-540X 1996/12 [Not refereed][Not invited]
     
    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 2169-9313 1996/11 [Refereed][Not invited]
     
    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.

Books etc

  • リモートセンシング事典
    古屋正人 (Contributor7-11 氷河の流動と変動)
    日本リモートセンシング学会 2022/12 (ISBN: 9784621307762)
  • 図説地球科学の事典
    古屋 正人 (Contributor5.7 地球回転)
    朝倉書店 2018/04
  • 地形の辞典
    古屋 正人 (Contributor)
    朝倉書店 2017/02
  • 地球惑星科学入門、第1章
    古屋 正人 (Contributor)
    北海道大学出版会 2010
  • マグマダイナミクスと火山噴火
    古屋 正人 (Contributor)
    朝倉書店 2002

MISC

Awards & Honors

  • 2021/05 Volcanological society of Japan Excellent paper award
     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: Shohei Narita;Taku Ozawa;Yosuke Aoki;Masanobu Shimada;Masato Furuya;Youichiro Takada;Makoto Murakami
  • 2010 エスペック環境研究奨励賞
  • 2010 ESPEC Prize for the Encouragement of Environmental Studies
  • 2007 Guy Bomford Prize
  • 2004 日本火山学会論文賞
  • 2004 Best paper award
  • 2000 日本測地学会坪井賞
  • 2000 The Tsuboi Prize of the Geodetic Society of Japan

Research Grants & Projects

  • JSPS：Kakenhi Kiban (B)
    Date (from‐to) : 2023/04 -2028/03 
    Author : Masato Furuya, Mamoru Ishikawa, Go Iwahana, Kazuki Yanagiya
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (A)
    Date (from‐to) : 2020/04 -2025/03 
    Author : Shin Sugiyama, Hironobu Suga, Masato Furuya, Shigeru Aoki
     
    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。
  • Post-wildfire ground deformation over permafrost area: detection and modeling of spatial-temporal changes
    MEXT：Grand-in-aid for scientific research, Kiban (C)
    Date (from‐to) : 2019/04 -2022/03 
    Author : FURUYA Masato
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2020/03 
    Author : FURUYA Masato
     
    【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
    Date (from‐to) : 2018/04 -2019/03 
    Author : 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
    Date (from‐to) : 2017/04 -2018/03 
    Author : 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
    Date (from‐to) : 2016/04 -2017/03 
    Author : 古屋 正人
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2011/04 -2015/03 
    Author : SUGIYAMA SHIN, SAWAGAKI Takanobu, NAITO Nozomu, FURUYA Masato, ENOMOTO Hiroyuki
     
    We carried out satellite and field measurements to study the role of glacier dynamics in rapid retreat of calving glaciers. Glacier front positions and ice speed over the entire area of Southern Patagonia Icefield were quantified from 1984 to 2011. Details of the data revealed the fundamental role of glacier dynamics in the significantly large retreat observed in several glaciers. Lake measurements confirmed the influence of bed geometry on glacier stability, and unique lake temperature structures in front of calving glaciers. We also performed hot water drilling on glaciers on Livingston Island in Antarctic Peninsula. Subglacial and englacial measurements provided us clues to understand the mechanism of short-term ice speed variations. These results demonstrated that the glacier dynamics is a key driver of the recent rapid retreat of calving glaciers, and also suggested potentially important role of ice-lake interactions in the glacier change.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : FURUYA Masato
     
    Glacier surge exhibits order(s)-of-magnitude faster surface velocities during the short active phase, accompanying terminus advances and ice-thickness changes. However, the generation mechanisms remain uncertain because of the limited observations of surging glaciers that repeat the active phase after the decades-long quiescent phase. Here we use satellite synthetic aperture radar (SAR) images to examine the spatial-temporal changes in surface velocities, aiming to understand the mechanisms. We first identified surging glaciers at the West Kunlun Shan, NW Tibet. During the more-than-5-years-long active phase, we could detect clear seasonal modulations in their speeds that accelerated from fall to winter. In addition, we have discovered winter speed-up signals at the quiescent surge-type glaciers in Yukon, Canada. Namely, surge-type glaciers can accelerate even in the absence of surface meltwater input, suggesting the presence of englacial water and its rerouting toward the base.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2009 -2011 
    Author : OIKAWA Jun, FURUYA Masato, IGUCHI Masato, AOKI Yosuke, WATADA Shingo
     
    Suwanose-jima is one of the most active volcano of Japan with quasi-continuous unrest since 1957. It is monitored with broadband seismometers and tiltmeters but the difficulty in ground access to the island prohibits us to construct large-enough network to understand the magma plumbing system solely from the ground-based monitoring network. Ground deformation observed by the InSAR analysis thus has a potential to gain moreinsights into our understanding of the magma plumbing system of this volcano.We analyzed 43 images (19 ascending and 24 descending images, respectively) taken between March, 2007, and February, 2011. Despite strong explosive eruption activity in2007-2011, no deformation was detected for interferograms from all possible pairs except for small (several centimeters of line-of-sight changes) deformaiton in an interferogram between August 17, 2007, and January 2, 2008, which could represent deformation due to explosive eruptions in December, 2007. Explosive eruptions without significant deformation can be interpreted as eruptions without feeding magma from depth or magma propagation through the conduit without deformation.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2008 -2010 
    Author : HEKI Kosuke, FURUYA Masato
     
    Coseismic gravity changes associated with the 2010 Chile Earthquake have been detected with GRACE satellites (Heki & Matsuo, 2010 GRL). We also detected ice loss amounting up to 40 Gt/yr in the Asian High Mountains including the Himalayan glaciers (Matsuo & Heki, 2010 EPSL). We also revealed that quadratic signals in time-variable gravity are due mainly to linear changes in precipitation (Ogawa et al., 2011 GJI).
  • Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(B))
    Date (from‐to) : 2007 -2009 
    Author : Masato FURUYA, Youichiro TAKADA
     
    Using SAR data, we detected crustal deformation signals associated with several inland earthquakes in and around continental plate boundaries. All the data revealed unexpected signals that could not be predicted from the prompt seismological estimates of the fault sources, and thus would be overlooked if SAR were not used. We discovered a long-lasting afterslip due to the M5 earthquake at the Chaman fault, Afghanistan. All the events, including the 1996 Onikobe, 2007 Chuetsu-oki, 2008 Iwate-Miyagi, 2008 Yutian, 2008 Wenchuan, revealed complex crustal displacements that could not be explaine...
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2008 -2008 
    Author : KONAGAI Kazuo, CHIGIRA Masahiro, SHIOHARA Hitoshi, HIRATA Naoshi, MORI James J., KUWAHARA Yasuto, FURUYA Masato, SUN Wenke, IKEDA Yasutaka, ATSUMI Tomohide, KAMAI Toshitaka, FUKUOKA Hiroshi, WANG Fawu, TAKAHASHI Yoshikazu, OHMACHI Tatsuo, KAWASHIMA Kazuhiko, KONO Susumu, KABEYASAWA Toshimi, NAKANO Yoshiaki, MIYAZAWA Masatoshi, TOBITA Mikio, SHIMADA Masanobu, KANO Kenichi, LIN Weiren, TATANO Hirokazu, YAMORI Katsuya, KAJITANI Yoshio
     
    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))
    Date (from‐to) : 2002 -2003 
    Author : 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...
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2001 -2003 
    Author : WENKE Sun, FURUTA Masato, OKUBO Shuhei
     
    Mainly theoretical research was performed : 1.The effects of the Earth's curvature and radial heterogeneity in dislocation studies were studied, though comparing the coseismic deformations caused by dislocations in half space and homogeneous spherical earth models, a homogeneous sphere and a layer spherical model. It was learnt that both the effects are large. 2.To overcome the disadvantages of the current dislocation theories, a new theory for calculating asymptotic deformations excited by a point dislocation in a spherical symmetric earth model was presented. This theory is given by a closed form of mathematical expressions, so that it is mathematically simple and can be applied easily. Moreover, since the asymptotic theory includes sphericity and vertical structure effects, it is physically more reasonable than the flat-earth theory. 3.The crustal deformation caused by the 2000 Miyakejima volcanic and seismic activities was studied. 4.The co-seismic deformation in spectrum was also considered, so that the ability of satellite gravity missions to detect co-seismic geoid and gravity changes were observed and determined. 6.The expressions of co-seismic strains were derived. The results were presented in different national/international conferences, and published in 8 papers.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2001 -2003 
    Author : OKUBO Shuhei, SUN Wenke, FURUYA Masato, HIBIYA Toshiyuki
     
    We formulated the gravity, geoid height and elevation changes due to fault motoin in a Maxwell viscoelastic earth. The formulation is implemented to a FORTRAN computer code, which enables us to compute interseismic gravity/elevation changes during an earthquake cycle based on the Savage's backslip model. We applied the technique to the interseismic deformation around the Tokai area where the Philippine Sea plate is subducting beneath the Eurasian plate. The model successfully reproduces the steady subsidence when we assume reasonable viscosity profile and asperity distribution. On the contrary, we find the computed gravity change rate is significantly larger than the observed one. The result casts profound doubt on the validity of the Savage's supposition that no deformation accumulates over repeated seismic cycles. We applied the formulation to the analysis of gravity change before and after the Tokachi-oki Earthquake (M8.1, September 26, 2003). To be more specific, we calculated the interseismic gravity change rate to reduce the absolute gravity value taken several years before the earthquake to the one just before the earthquake. When compared with the absolute gravity value just after the earthquake, it enables us to estimate the coseismic gravity change. The change agrees well with the theoretically predicted one.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 1998 -2000 
    Author : OKUBO Shuhei, FURUYA Masato, HIBIYA Toshiyuki
     
    1. We carried out a research to eliminate the meteorological disturbance on the differential interferometry of SAR data by using a JMA regional numerical model. The technique enables us to detect long wavelength undulated fringes at western coast of Korean Peninsula by ERS-1 satellite radar interferometry. Though the amplitude in the derived interferogram is larger than that of prediction, the spatial pattern is similar to the theoretical computation of inland flexural response to the ocean tide in the Yellow Sea. 2. We developed a recipe to compute gravity/geoid height change and vertical displacement caused by a point dislocation in a spherical, viscoelastic and self-gravitating earth. It enables us to trace the crustal deformation excited by a great earthquake. Time evolutions for a point source located in the elastic lithosphere is distinctively different from that when a source is in the viscoelastic asthenosphere. 3. As a first step toward a numerical modeling of global internal tide field, the distribution of the M2 internal tide in the North Pacific is examined using a three-dimensional primitive equation numerical model. The numerical simulation shows that energetic internal tides are generated over the prominent bottom topographies in the Indonesian Archipelago, the Solomon Archipelago, the Aleutian Archipelago as well as over the continental shelf slope in the East China Sea, the Izu-Ogasawara Ridge and the Hawaiian Ridge. In particular, the calculated spatial distribution of the M2 internal tide around the Hawaiian Ridge agrees very well with that obtained from the Topex/Poseidon altimetry.
  • 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
    Date (from‐to) : 1997

Educational Activities

Teaching Experience

  • Advanced Course in Remote Sensing Applications
    開講年度 : 2021
    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
  • Advanced Crustal Dynamics
    開講年度 : 2021
    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
  • Laboratory Work in Earth and Planetary Sciences IV
    開講年度 : 2021
    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
  • Freshman Seminar
    開講年度 : 2021
    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
  • Space Geodesy
    開講年度 : 2021
    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

Committee Membership

  • 2023/07 -2027/07   International Association of Geodesy, Executive Committee   Member-At-Large
  • 2023/10 -2024/03   Progress in Earth and Planetary Science   Journal Editorial Board Member
  • 2021/03 -2021/06   European Space Agency, Fringe 2021 Workshop   Science Committee Member
  • 2016/07 -2020/12   Earth Planets Space   Vice Editor-in-chief

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