Tokyo, Japan
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Yamamoto H.,Taisei Corporation | Onuma T.,JGI Inc. | Kumagai T.,JGC Corporation | Rutqvist J.,Lawrence Berkeley National Laboratory
Harmonising Rock Engineering and the Environment - Proceedings of the 12th ISRM International Congress on Rock Mechanics | Year: 2012

DInSAR (differential interferometric synthetic aperture radar) is a promising technology for measuring, in remarkable detail, spatial surface deformations due to pressurization of reservoirs during CO 2 injection.We performed coupled fluid-flow and geomechanical simulations for an example corresponding to the geometry and conditions at the In Salah CO 2 storage project, Algeria. The time evolution of surface displacement detected by DInSAR was quantitatively well reproduced by the simulation.Asensitivity study suggests that information on theCO 2 front is indirectly transferred to the surface displacement, and thus, even if the CO 2 flow were highly localized due to reservoir heterogeneity such as faulting, surface deformation does not sharply reflect the flow patterns, but are smoothened.Temporal and spatial changes in surface deformation interpreted from DInSAR potentially provide a unique opportunity for calibrating the spatial permeabilities (e.g. low-permeability barriers) of reservoir models. © 2012 Taylor & Francis Group, London.

Ishiyama T.,University of Tokyo | Sato H.,University of Tokyo | Abe S.,JGI Inc. | Kawasaki S.,JGI Inc. | Kato N.,University of Tokyo
Tectonophysics | Year: 2016

We collected and interpreted high-resolution 3D seismic reflection data across a hypothesized fault scarp, along the largest active fault that could generate hazardous earthquakes in the Tokyo metropolitan area. The processed and interpreted 3D seismic cube, linked with nearby borehole stratigraphy, suggests that a monocline that deforms lower Pleistocene units is unconformably overlain by middle Pleistocene conglomerates. Judging from structural patterns and vertical separation on the lower-middle Pleistocene units and the ground surface, the hypothesized scarp was interpreted as a terrace riser rather than as a manifestation of late Pleistocene structural growth resulting from repeated fault activity. Devastating earthquake scenarios had been predicted along the fault in question based on its proximity to the metropolitan area, however our new results lead to a significant decrease in estimated fault length and consequently in the estimated magnitude of future earthquakes associated with reactivation. This suggests a greatly reduced seismic hazard in the Tokyo metropolitan area from earthquakes generated by active intraplate crustal faults. © 2016 Elsevier B.V.

Sato H.,University of Tokyo | Kato N.,University of Tokyo | Abe S.,JGI Inc. | Van Horne A.,University of Wyoming | Takeda T.,Japan National Research Institute for Earth Science and Disaster Prevention
Tectonophysics | Year: 2015

In models for strain-partitioning at obliquely-convergent plate boundaries, trench-parallel slip occurs on a vertical fault. Trench-parallel slip at the Nankai subduction zone, SW Japan, is mapped along the Median Tectonic Line (MTL) which dips approximately 40°N. To understand its structural context and how the MTL functions in this slip-partitioned system, we collected a set of three seismic profiles in the Kii peninsula south of Osaka, using a multi-scale acquisition strategy that provides increasingly fine resolution. To understand its fault kinematics, we analyzed microseismic activity in two locations on the fault, using source data from Japan's Hi-net monitoring network. Structural details suggest that the MTL functioned as a megathrust during subduction of the Cretaceous Sanbagawa HP metamorphic belt. Its current pattern of microseismicity shows that it behaves as a strike-slip fault with no indication of a vertical fault at or around its surface trace. Thus, trench-parallel slip at the Nankai is now accommodated on an inclined fault plane in an unusual form of partitioning. This system appears to have developed out of a two-phase tectonic history in which a thrust structure that formed under initial-phase compressive stresses has been reactivated as a strike-slip fault under subsequent-phase shear stresses. Its unusual kinematics show that shear failure can occur on an existing non-vertical fault plane at a regional scale in preference to the rupture of a new ideal (vertical) fault plane. © 2015 Elsevier B.V.

Ishiyama T.,University of Tokyo | Sato H.,University of Tokyo | Kato N.,University of Tokyo | Nakayama T.,University of Tokyo | Abe S.,JGI Inc.
Geophysical Research Letters | Year: 2013

The Tokyo metropolitan area, underlain by Neogene and Quaternary sediments more than 5 km thick, is currently deformed by blind thrusts that could generate hazardous earthquakes. However, their little geomorphic expression and dense urbanization make understanding of folds produced above them and recent deformation highly elusive. Here we show subsurface geometries of several active blind thrusts beneath this highly urbanized area, based on tectonic landforms, high-resolution seismic reflection data, and Quaternary stratigraphy. Deep seismic reflection profiles corroborate the notion that steeply dipping blind thrusts are reactivated normal faults originally formed by middle Miocene extensional tectonics. Despite very slow (less than 0.1 mm/yr) late Quaternary slip rates, our work suggests the presence of previously unrecognized faults that pose seismic hazards to Tokyo and outlying communities, highlighting the need for additional information to define recent slip rates, magnitude, and recurrence of past earthquakes on them. © 2013 American Geophysical Union. All Rights Reserved.

Arai R.,University of Tokyo | Arai R.,University of Hawaii at Manoa | Iwasaki T.,University of Tokyo | Sato H.,University of Tokyo | And 2 more authors.
Journal of Geophysical Research: Solid Earth | Year: 2013

The Izu-Bonin arc (IBA) has been colliding with the more northerly Honshu arc since the middle Miocene, forming a globally unique active Izu arc-arc collision zone (ICZ) in central Japan. To determine crustal structure of the ICZ, we constrain P and S wave velocities from active source refraction data. The velocity structures reveal that the style of collisions of the Misaka, Tanzawa, and Izu blocks, which were derived from the IBA, has been controlled by subduction of the IBA. High-velocity rocks (Vp > 6.2 km/s) observed in the ICZ continuously extend to deeper crust, suggesting that plutonic rocks, formed by partial melting of the subducted IBA crust, intruded into the Honshu arc crust and the accreted crustal blocks of the IBA. The northernmost major fault in the ICZ dips southeastward, which is in clear contrast with other major northwestward dipping faults farther southeast. In the northernmost part of the ICZ, the upper 5 km crust of the Misaka block was delaminated from its lower part and obducted onto the Honshu arc. The Tanzawa block, southeast of the Misaka block, is bounded by northwestward dipping faults and is characterized by crustal stacking. A low-velocity sedimentary layer between the Tanzawa and Izu blocks dips northwestward along the collisional boundary and reaches ~5 km depth, suggesting that the Izu block underthrust beneath the Tanzawa block. The overall geometry of the collisional boundaries exhibits a doubly vergent system, which is characterized by inward-dipping thrust faults on both sides. Key Points Crustal structure in the Izu collision zone is investigated The collisional boundaries exhibit doubly vergent system The subducted Izu-Bonin arc crust produced high-velocity plutonic rocks ©2013. American Geophysical Union. All Rights Reserved.

Onuma T.,JGI Inc. | Okada K.,JGI Inc. | Otsubo A.,Japan Petroleum Exploration Co.
Energy Procedia | Year: 2011

History of surface deformation related with CO 2 injection at In Salah Gas Project, Algeria, was analyzed using satellite-borne Synthetic Aperture Radar (SAR) data. The Project is widely known as long term CO 2 storage project, of which injection has been performed since August 2004, with injected amount of 0.75 million tons CO 2 per year. Surface deformation around three injection wells, KB-501 through KB-503, has been analyzed by Differential Interferometry SAR (DInSAR), a promising remote sensing technique to detect surface deformation at an order of millimeters, using 47 scenes of ENVISAT ASAR spanning from July 2003 to May 2010. Amongst three injection wells, CO 2 injection at KB-502 has been temporarily shut down in July 2007, due to CO 2 breakthrough at an appraisal well KB-5 located 1.3km to the northwest of KB-502. Permanent decommission of KB- 5 was completed and the injection at KB-502 was restarted in November 2009. DInSAR analysis has revealed the surface displacement pattern between July 2007 and May 2010 around KB-502, which is thought to be related with shut-down and recommencement of CO 2 injection. © 2011 Published by Elsevier Ltd.

Asakawa E.,JGI Inc. | Hayashi T.,JGI Inc. | Tsukahara H.,JGI Inc.
75th EAGE Conference and Exhibition Incorporating SPE EUROPEC 2013 | Year: 2013

The first offshore methane hydrate production test will be conducted by METI and JOGMEC/MH21 in early 2013 in the eastern Nankai Trough, Japan. The test aims to prove the applicability of the depressurization technique for MH production. The flow test intervals will be at shallow sediment depths but at deep water depths. JOGMEC plans to carry out a multi-component seismic survey to monitor the dissociation of MH by the depressurization technique in the flow test scheduled in early 2013. JGI, Inc. has developed deep-water OBC system (Deep-sea Seismic System, DSS) with OCC Corp. and deployed the DSS close to the production test well in August 2012. After deployment, the DSS system was buried by ROV. Then we carried out the baseline 2D/3D multicomponent seismic survey. The results show the good quality to delineate the methane hydrate concentrated zone. After the baseline survey, we have left the DSS on seafloor and remains there until the monitoring surveys scheduled in April and August 2013, because the fixed location of the sensors is crucial for time-lapse monitoring survey.

Arai R.,University of Tokyo | Arai R.,University of Hawaii at Manoa | Arai R.,Japan Agency for Marine - Earth Science and Technology | Iwasaki T.,University of Tokyo | And 3 more authors.
Geochemistry, Geophysics, Geosystems | Year: 2014

We show contrasting subduction structures within the Philippine Sea plate inferred from active-source wide-angle reflection data. Previous studies showed that large-amplitude reflections from the slab are observed in southwest Japan and indicated that a thin low-velocity layer with a high fluid content is formed along the top of the subducting oceanic crust. On the contrary, we found that the slab reflections have smaller amplitudes in the Izu collision zone, central Japan, where the Izu-Bonin volcanic arc has been colliding/subducting, suggesting that such a low-velocity layer does not exist beneath the collision zone. This structural difference is also supported by P-wave and S-wave velocity anomalies by passive-source tomography and electrical conductivity, and correlates with the regional distribution of deep tremors and intraslab earthquakes, both of which are induced by dehydration processes within the downgoing slab. Based on these comparisons, we suggest that the original structure of the incoming plate controls the contrasting subducting systems: typical oceanic plate absorbs water by hydrothermal circulation at spreading centers and/or seawater infiltration at outer rises, whereas volcanic arc crust consumes a large amount of hydrous minerals for melt production and metamorphoses to more stable, anhydrous forms before subduction. Key Points We show contrasting subduction structures of the Philippine Sea plate Dehydration is active in Nankai subduction zone but not in Izu collision zone The structural difference is the main cause for the zoned pattern of seismicity © 2014. American Geophysical Union. All Rights Reserved.

Mitsuhara N.,JGI Inc. | Onuma T.,JGI Inc.
34th Asian Conference on Remote Sensing 2013, ACRS 2013 | Year: 2013

The surface geology of the Zagros Mountains and northwestern part of Iraq are interpreted by using false-color composite images. The study area is characterized by dry climate and hence sparse vegetation cover, which makes the spectral analysis using shortwave infrared and thermal infrared data acquired by Terra ASTER applicable to geological mapping. The mineral indices images which might indicate the influence of hydrocarbon seepage are prepared by using Terra ASTER SWIR bands. Several localities were extracted as having anomalous concentration of calcite and clays, when cross-checked with background geological context. ALOS PALSAR data has helped delineate ENE-WSW trending folds which are thought to be related with the graben system in northwest part of Iraq by emphasizing the difference of subtle surface relief among exposed rocks. Copyright© (2013) by the Asian Association on Remote Sensing.

Aoki N.,JGI Inc. | Asakawa E.,JGI Inc. | Abe S.,JGI Inc.
Society of Petroleum Engineers - International Petroleum Technology Conference 2014, IPTC 2014: Unlocking Energy Through Innovation, Technology and Capability | Year: 2014

Surface based microseismic monitoring during hydraulic fracture stimulations is an emerging technology in the last decade. The method observes acoustic emission (AE) or microseismic events using a surface receiver array and estimates source locations and origin times of the events by analyzing a time series of migration images from observation data. However, the accuracy and monitoring cost of the technology highly depends on the array-geometry. The migration images can be blurred if a too coarse array is used. Monitoring cost can be unnecessarily high if a too dense array is used. Some sort of adequate array evaluation methods are required for designing a cost effective survey plan. We introduce an array evaluation method based on the point-spread function (PSF). The PSF describes the response of an imaging system to a point source. Our proposed method evaluates an array in the following way: First, a point source of which excitation time and source location are known is defined. Second, synthetic seismograms using the array are computed. Third, the synthetic traces are migrated and a time series of source images are obtained. Finally, the images are examined so that the abilities of the array are understood. We demonstrate the method by diplaying attributes calculated from the dataset which represent the precision and accuracy of the source location determination. Copyright 2014, International Petroleum Technology Conference.

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