Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer   Participation form：Joint(The main charge)  

Volcanic activity generally causes crustal deformation, which sometimes induces groundwater changes, and both of these phenomena are sometimes detected before volcanic eruptions. Therefore, investigations of crustal deformation and groundwater changes can be useful for predicting volcanic eruptions. The Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, has been observing groundwater pressure at Ohtaki observatory(GOT) since 1998. GOT is about 10 km southeast of the summit of Mt. Ontake. During this observation period, Mt. Ontake has erupted twice, in 2007 and in 2014. Before the 2007 eruption, the groundwater pressure at GOT clearly dropped, but it did not change before or after the 2014 eruption. These observations are consistent with the crustal deformation observed by Global Navigation Satellite System stations of the Geospatial Information Authority of Japan. The difference between the 2007 and 2014 eruptions can be explained if a relatively large magma intrusion occurred before the 2007 eruption but no or a small magma intrusion before the 2014 eruption.

DOI： 10.1186/s40623-016-0420-6

Other Link： http://db.spins.usp.ac.jp/html/200000240_ja.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union   Participation form：Joint(The vice charge)  

DOI： 10.1002/2013GL058322

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Hydrological and geochemical studies for earthquake prediction in Japan during the last two decades are reviewed. Following the 1995 Hyogo-ken Nanbu (Kobe) earthquake, the central approach to research on earthquake prediction was modified. Instead of precursory detection, emphasis was placed on understanding the entire earthquake cycle. Moreover, the prediction program for the anticipated Tokai earthquake was revised in 2003 to include the detection of preslip-related precursors. These changes included the promotion of the following hydrological and geochemical studies for earthquake prediction: (1) development and/or application of statistical methods to extract small fluctuations from hydrological/geochemical data, (2) evaluation of the detectability of preslip-related anomalies in terms of groundwater levels in wells in the Tokai region, and (3) establishment of a new groundwater and borehole strain observation network for Nankai and Tonankai earthquake prediction research. The following basic geochemical studies were carried out: (1) development of a new monitoring system using a quadrupole mass spectrometer, (2) experimental studies on hydrogen generation by the grinding of rock and crystal powders, (3) comprehensive monitoring of groundwater gas and precise crustal deformation, and (4) mantle-derivative helium observation to compare with seismic velocity structures and the distribution of non-volcanic tremors. Moreover, hydrological and geochemical investigations related to the evolution of fault zones were introduced within the framework of fault zone drilling projects.

DOI： 10.1007/s11069-011-9980-8

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Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

This study evaluates a method that enhances detection of non-volcanic low frequency tremor (NVT) using VA-net, a 3-level vertical seismic array network that was recently constructed in southwest Japan. The method employs semblance analysis for continuous vertical array records and calculates semblance coefficients as a function of time and apparent vertical velocity. The sign of the best apparent velocity provides information about propagation direction, either upward or downward, allowing easy discrimination between seismic signals of natural origin and unwanted noise such as man-made vibrations. We applied the method to a NVT episode that occurred beneath the Kii Peninsula during November 2008, to demonstrate that NVT signals can be detected using only the 3-level array. Furthermore, we demonstrate that the method enables us to detect minor NVT activity which is not detected by a conventional envelope cross-correlation method, resulting in a dramatic improvement in detection capability. Citation: Imanishi, K., N. Takeda, Y. Kuwahara, and N. Koizumi (2011), Enhanced detection capability of non-volcanic tremor using a 3-level vertical seismic array network, VA-net, in southwest Japan, Geophys. Res. Lett., 38, L20305, doi: 10.1029/2011GL049071.

DOI： 10.1029/2011GL049071

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

Oscillations of water pressures and crustal strains due to the seismic waves of the 2010 Chile earthquake were observed in Japan. The oscillations of water pressures observed over the frequency range of 0.002 to 0.1 Hz were negative proportional to the oscillations of volumetric strains. The responses of water pressures in closed wells are frequency-dependent. The expression for the response of water pressure in a closed well to crustal strain is developed based on the poroelastic theory. The expression developed in the present paper describes the frequency characteristics of the responses. The response is useful for the estimation of rock properties. In addition, the responses of water pressure due to tidal volumetric strain are estimated and compared with the responses due to the seismic waves.

DOI： 10.1029/2010JB007794

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer   Participation form：Joint(The vice charge)  

DOI： 10.1007/s11069-011-9980-8

Language：Japanese   Publisher：The Geological Society of Japan  

DOI： 10.5575/geosoc.117.1.I_II

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER BASEL AG  

In 2006, we started construction of an observation network of 12 stations in and around Shikoku and the Kii Peninsula to conduct research for forecasting Tonankai and Nankai earthquakes. The purpose of the network is to clarify the mechanism of past preseismic groundwater changes and crustal deformation related to Tonankai and Nankai earthquakes. Construction of the network of 12 stations was completed in January 2009. Work on two stations, Hongu-Mikoshi (HGM) and Ichiura (ICU), was finished earlier and they began observations in 2007. These two stations detected strain changes caused by the slow-slip events on the plate boundary in June 2008, although related changes in groundwater levels were not clearly recognized.

DOI： 10.1007/s00024-010-0095-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TERRA SCIENTIFIC PUBL CO  

Between 2001 and 2005, the Disaster Prevention Research Center of National Cheng-Kung University established a groundwater observation network consisting of 16 wells. Most of these were located along active faults for research on earthquake-related groundwater changes. They were selected mainly from among the 550 groundwater observation wells of the Water Resources Agency (WRA), which monitors and manages groundwater resources in Taiwan. The groundwater level was observed at a resolution of 0.2 mm at the wells. The depths of the well screens ranged between 80 and 252 m. Groundwater level data at six of the 16 wells were analyzed between 2003 and 2006 in an evaluation of such data for use in detecting earthquake-related groundwater level changes. The strain sensitivities of the groundwater level at these six wells ranged between 0.1 and 0.5 mm/10(-9), indicating that an analysis of groundwater level data at these six wells can detect volumetric strain changes on the order of 10(-9). Coseismic and/or postseismic groundwater level changes associated with 17 earthquakes in and around Taiwan whose magnitudes were >= 6 were also analyzed. Our analysis shows that ground shaking seems the main reason for earthquake-related changes but that the acceleration of ground shaking cannot always explain the observed groundwater level changes.

DOI： 10.5047/eps.2009.12.008

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Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.5575/geosoc.116.374

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Geological Society of Japan  

We determined the stress history in the forearc region of the Nankai trough subduction zone by examinug boreholes at the Miyama and Ichiura observation wells, located on the northern and southern margins of the northern unit of the Kumano Acidic Rocks, respectively, eastern Kii Peninsula, SW Japan. To estimate paleostress, the multiple inverse method was applied to fault planes identified within the core samples; to estimate the present-day stress, the borehole breakout method was used. The results obtained using the multiple inverse method indicate that the two observation wells have similar stress histories, involving E-W compressive stress followed by NE-SW extensional stress and finally N-S compressive stress. The present-day maximum horizontal compressive stress (σ_hmax) at the Miyama observation well trends E-W, consistent with the present-day regional stress in SW Japan and different from the final stage of stress determined by the multiple inverse method. The present-day σ_hmax at the Ichiura observation well trends NNE-SSW, similar the final stage of stress determined by the multiple inverse method. These findings indicate that the boundary between the areas of E-W compressive stress (characteristic of SW Japan) and N-S compressive stress (influenced by subduction of the Philippine Sea Plate) has gradually migrated southward over time.

DOI： 10.5575/geosoc.115.457

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer  

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Language：English   Publishing type：Research paper (scientific journal)   Participation form：Joint(The vice charge)  

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union   Participation form：Joint(The main charge)  

DOI： 10.1029/2004GL019557

Language：English   Publisher：The Seismological Society of Japan, Society of Geomagnetism and Earth, Planetary and Space Sciences, The Volcanological Society of Japan , The Geodetic Society of Japan , The Japanese Society for Planetary Sciences  

A regional continuous Global Positioning System (GPS) array, consisting of uniform antenna type, has been established by the Geological Survey of Japan (GSJ) mainly around the Kansai district. Geodetic results for 2.5 years data are as follows. In comparison with the solutions obtained from the Geographical Survey Institute (GSI) continuous GPS array which employs different type of antenna from the GSJ's array, itwas found that the agreements between the daily positions were about 10 mm in horizontal and 15 to 20 mm in vertical components. This result indicates that the influence of the antenna type difference is at this level. The GSJ's GPS stations around the Kansai district were found to have a common annual variation in the vertical component, whose amplitude was different from site to site. There were small correlations with in situ measurements of groundwater-level variation, except for the two stations whose annual variations of the GPS vertical component were the largest. The vertical displacements due to elastic deformation by groundwater-pressure changes in the aquifers were estimated using a simple model, but they were too small to account for the observed variations.

DOI： 10.1186/BF03352260

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER GEOPHYSICAL UNION  

In order to understand the mechanism of material transport induced by seismic and volcanic activities, we analyzed chemical changes and permeability variations based on field observations on a recently active volcano, Izu-Oshima. From March to August 1988, when the volcanic and seismic activities in Izu-Oshima declined following an episode of those activities that ended in late 1987, the concentrations of CO2 and H(2 )of volcanic origin increased 10-30 times above the previous levels in the Koshimizu Well located 1 km from the coast. Analysis of tidal-frequency groundwater level variations in the well shows changes in tidal response of the groundwater level that are inferred to be associated with changes in shallow formation permeability. A simple 1-dimensional diffusion model, together with reasonable assumption about the local hydrologic structure, suggest that the horizontal permeability in the upper few hundred meters of the island is high, of the order of 10(-8) m(2), and varied by as much as 20 percent during recorded period. We consider that these changes should be the results of vertical development of cracks which was caused by hot water intrusion from magma.

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Authorship：Lead author  

DOI： doi.org/10.4294/zisin1948.48.3_315

Authorship：Lead author   Language：Japanese  

DOI： doi.org/10.18940/kazan.39.4_169

Authorship：Lead author   Language：English  

DOI： doi.org/10.4294/jpe1952.39.631

Language：English   Publishing type：Doctoral thesis  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Geophysical Union   Participation form：Joint(The main charge)  

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (other academic)  

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：国土地理院  

気象庁震度データベースを用いた地震予測の2021年分の予測結果の評価と 2022年の新たな予測の紹介．

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：国土地理院  

気象庁震度データベースを用いた地震予測と2015-2021年の予測の評価

Language：Japanese   Publishing type：Research paper (other academic)   Publisher：日本地震学会   Participation form：Joint(The main charge)  

Other Link： https://www.zisin.jp/publications/pdf/nf-vol127.pdf

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：国土地理院   Participation form：Joint(The main charge)  

Other Link： https://cais.gsi.go.jp/YOCHIREN/report/index106.html

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：国土地理院  

気象庁震度データベースを用いた地震予測と2015-2020年の予測の評価

Other Link： https://cais.gsi.go.jp/YOCHIREN/report/kaihou105/12_08.pdf

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Publisher：国土地理院  

気象庁震度データベースを用いた2019年の地震予測結果の評価と2020年の予測

Other Link： https://cais.gsi.go.jp/YOCHIREN/report/index104.html

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：滋賀県立大学環境科学部   Participation form：Joint(The main charge)  

Other Link： http://www.ses.usp.ac.jp/nenpou/np23/np23-008-012.pdf

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：Association for the Development of Earthquake Prediction   Participation form：Joint(The main charge)  

Other Link： http://www.tries.jp/research/doc/2019060420211642_63.pdf

Language：Japanese   Publishing type：Research paper (conference, symposium, etc.)   Participation form：Joint(The main charge)  

活断層は、数千年～数万年に1 回程度の頻度で断層運動（大地震）を起こして環境を破壊する。他方、地震を起こさない期間においては、断層面周辺の破壊によって生じた面状の高透水性構造が、地下水流動を促進し、地下水による熱・物質供給を通して環境を形成・維持するという側面を持つ。日本最古かつ最大の湖であり，周囲の陸上の活断層の調査も進んでいる琵琶湖において，湖底断層とその周辺の水を研究することは，上記の後者の役割を明らかにする上で効率的である．また，琵琶湖が，滋賀・大阪・京都の貴重な水源でもある事を考えれば重要でもある．このような観点にたって，平成30 年8 月29 日に，滋賀県立大学において，「湖底断層研究会」のキックオフワークショップを開催し,湖底断層研究における現状と課題について議論した．本報告書は，ワークショップの発表内容について紹介である．一般に環境破壊リスクとのみ考えられている活断層の別の側面について，読者にも考えていただければ幸いである．

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：地震予知総合研究振興会   Participation form：Joint(The main charge)  

気象庁の震度データベースを用いた簡易な地震予測手法の紹介と検証．

Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：Geological Survey of Japan, AIST   Participation form：Joint(The vice charge)  

We compared the coseismic well water level rises (Cw) and the strong ground motions during the 1999 Chi-Chi, Taiwan, earthquake in the Quaternary alluvial fan near the hypocentral region using data produced by the dense networks of strong ground motion and groundwater observation. The correlation between the Cw of the shallowest aquifer (Layer 1) and the ground motion response spectra at 1 Hz (Sv(1.0)) is stronger than that at 0.1 Hz (Sv(0.1)). On the other hand, the correlation between the Cw of the deeper aquifers (Layers 2-1, 2-2, 3 and 4) and Sv (1.0) are weaker than that at 0.1 Hz. We also found the good correlation between the Cw and hydraulic conductivity in the all aquifers. It is difficult to estimate Cw only by the spectral amplitude even in a Quaternary alluvial fan, where the geological and geomorphological conditions are similar.

Language：English   Publishing type：Research paper (scientific journal)   Publisher：National Institute of Advanced Industrial Science and Technology  

DOI： doi.org/10.5571/syntheng.6.27

Language：Japanese   Publisher：National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan  

Geological Survey of Japan, AIST has been carrying out the cooperative research entitled "Hydrological and geochemical research for earthquake prediction in Taiwan" with Disaster Prevention Research Center, National Cheng-Kung University, Taiwan since 2002. We made much contribution to clarifying the mechanism of groundwater changes and their recoveries related to the 1999 Chichi earthquake, constructing a groundwater observation network composed of 16 wells in Taiwan and understanding the earthquake-related groundwater changes observed by the new groundwater observation network through this cooperative research. In Taiwan seismicity is more active and crustal deformation is more rapid than in Japan. Therefore observation and analysis of groundwater changes related to earthquake and crustal deformation in Taiwan will enable us to make rapid progress in hydrological and geochemical research for earthquake prediction. This cooperative research will also give important information for evaluation of long-term groundwater changes in tectonically active areas like Japan and Taiwan.

DOI： 10.9795/bullgsj.62.185

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Other Link： https://jlc.jst.go.jp/DN/JALC/00388437238?from=CiNii

Language：Japanese   Publisher：National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan  

We implemented a new analysis strategy for the routine GPS data analysis system of the continuous GPS network of the Geological Survey of Japan, AIST when two new continuous GPS observation stations in Shikoku and Kii Peninsula were installed in 2010. We updated the Bernese GPS software package from Version 4 to 5, and implemented some new methods such as estimation of the troposphere delay gradient as well as the zenith total delay. Comparing the result with that of the previous analysis strategy, we found that the repeatability of the GPS station coordinates were reduced especially in summer, which we inferred was due to the reduction of troposphere delay errors caused by the spatial variation of water vapor that dominated in summer season.

DOI： 10.9795/bullgsj.62.319

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Other Link： https://jlc.jst.go.jp/DN/JALC/10003554134?from=CiNii

Language：Japanese   Publisher：National Institute of Advanced Industrial Science and Technology, Geological Survey of Japan  

The detectability of hypothetical "preslip" of the great Tonanaki and Nankai earthquakes is investigated using the integrated groundwater observatories currently being established by the Geological Survey of Japan, AIST. The detectability is calculated in terms of three characteristic parameters of the preslip, i.e., time constant (slip duration), spatial extent, and direction of the preslip. If it is assumed that the crustal deformation caused by the hypothetical preslip follows the elastic dislocation theory, and the noise level of the line strain observation of the network is 2×10^-8, it is expected to detect preslip with a moment magnitude of greater than 6.5 in the wide area of the network when the characteristic time constant (duration of preslip) and the spatial extent of preslip are about 1 day and 12 km×10 km, respectively. The detectability gets worse when either of the quantities is larger.

DOI： 10.9795/bullgsj.60.511

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Other Link： https://jlc.jst.go.jp/DN/JALC/00347177991?from=CiNii

Language：Japanese   Publisher：Volcanological Society of Japan  

DOI： 10.18940/vsj.2001.2.0_121

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： doi.org/10.4294/zisin1948.44.3_155

Language：Japanese  

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Language：Japanese   Publisher：地震予知総合研究振興会  

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Language：Japanese   Publisher：地震予知総合研究振興会東濃地震科学研究所  

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Language：English   Publisher：BIRKHAUSER VERLAG AG  

To understand the detailed process of fault activity, aseismic slip may play a crucial role. Aseismic slip of inland faults in Japan is not well known, except for that related to the Atotsugawa fault. To know whether aseismic slip does not occur, or is merely not detected, is an important question. The National Institute of Advanced Industrial Science and Technology constructed an observation site near Yasutomi fault, a part of the Yamasaki fault system, and has collected data on the crustal strain field, groundwater pressures, and crustal movement using GPS. In a departure from the long-term trend, a transient change of the crustal strain field lasting a few months was recorded. It indicated the possibility of an aseismic slip event. Furthermore, analyses of data from the extensometers at Yasutomi and Osawa observation vaults of Kyoto University, as well as GPS data from the Geographical Survey Institute (GEONET), revealed unsteady crustal strain changes. All data could be explained by local, left-lateral, aseismic slip of the order of 1 mm in the shallow part of the Yasutomi fault.

DOI： 10.1007/s00024-006-0048-8

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Language：Japanese   Publisher：地震予知総合研究振興会東濃地震科学研究所  

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Language：Japanese   Publisher：地震予知総合研究振興会東濃地震科学研究所  

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Language：English   Publisher：TERRA SCIENTIFIC PUBL CO  

The 2004 off the Kii peninsula earthquakes (Mj7.1 and Mj7.4) occurred at the Nankai trough, on 5 September 2004. Clear strain-steps associated with these earthquakes were observed with Ishii-type borehole strainmeters and quartz-tube extensometers in the Tokai and Kinki districts', We investigated the spatial and depth distribution of the observed principal strain changes and compared the observed strain-steps and theoretical calculations at all observatories. The following results were obtained: the observed strain-steps at all observatories are generally consistent with the polarities of the theoretical values, and the observed strain-step increases with depth at the same place. As for the Togari site, the following relationships are obtained: the strain-step and the tidal strains increase with depth and increasing of the modulus of elasticity, namely, hardness of rock. We consider that the geological structure around the observatory may cause a modification of the strain field.

DOI： 10.5636/eps.57.4_309

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Language：Japanese   Publisher：実業公報社  

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Language：Japanese   Publisher：実業公報社  

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Language：English   Publisher：Springer Berlin  

Groundwater level and flow rate at 44 wells are continuously observed by the Geological Survey of Japan and the Shizuoka and Gifu Prefectural Governments for monitoring seismic and volcanic activities. The 2003 Tokachi-oki earthquake (M8.0) occurred off the south coast of Hokkaido Island, Japan on September 26, 2003. The epicentral distance to the nearest observation well is about 250 km and that to the farthest is about 1200 km. At the 22 wells, we detected changes in groundwater level or flow rate in relation to the earthquake. Most of the changes are coseismic step-like changes and/or short-period oscillations. In the nearest two observation wells, long-period oscillations with the periods of 39 and 53 minutes were also observed for several days after the earthquake, which is likely due to tsunami. In comparison between distributions of changes in groundwater level and theoretical coseismic strain by the fault model, it is clear that step-like increases were found in the contraction area of the coseismic strain. The relationship between amounts of the observed step-like groundwater-level changes and theoretical ones, calculated by the fault model using strain sensitivities of groundwater level indicates that the groundwater levels in the several wells responded to the coseismic strain. 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.

DOI： 10.1186/BF03353071

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Language：Japanese   Publisher：産業技術総合研究所地質調査総合センター  

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Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：オンライン  

Language：Japanese   Presentation type：Poster presentation  

Venue：オンライン  

Language：Japanese   Presentation type：Poster presentation  

Venue：伊賀市（オンライン）  

Language：Japanese   Presentation type：Poster presentation  

Venue：バーチャル  

Language：Japanese   Presentation type：Poster presentation  

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco  

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Venue：福島市  

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Venue：千葉市  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島市  

2016年熊本地震時〜地震後の地下水等の変化について説明した．

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Taipei  

Language：Japanese   Presentation type：Poster presentation  

Venue：千葉市  

道後温泉の地震後の水位変化について説明した．