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Nishi-Tokyo-shi, Japan

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.

Noguchi S.,Japan Oil, Gas and Metals National Corporation | Shimoda N.,Japan Oil, Gas and Metals National Corporation | Takano O.,Japan Oil, Gas and Metals National Corporation | Takano O.,Japan Petroleum Exploration Co. | And 6 more authors.
Marine and Petroleum Geology | Year: 2011

The reservoir architecture of methane hydrate (MH) bearing turbidite channels in the eastern Nankai Trough, offshore Japan is evaluated using a combination of 3-D seismic and well data. On the 3-D seismic section, the MH-bearing turbidite channels correspond to complex patterns of strong seismic reflectors, which show the 3-D internal architecture of the channel complex. A seismic-sequence stratigraphic analysis reveals that the channel complex can be roughly classified into three different stages of depositional sequence (upper, middle, and lower). Each depositional sequence results in a different depositional system that primarily controls the reservoir architecture of the turbidite channels. To construct a 3-D facies model, the stacking patterns of the turbidite channels are interpreted, and the reservoir heterogeneities of MH-bearing sediments are discussed. The identified channels at the upper sequence around the β1 well exhibit low-sinuosity channels consisting of various channel widths that range from tens to several hundreds of meters. Paleo-current flow directions of the turbidite channels are typically oriented along the north-northeast-to-south-southwest direction. High-amplitude patterns were identified above the channels along the north-to-south and north-northeast-to-south-southeast directions. These roughly coincide with the paleo-current flow of the turbidite channels. An interval velocity using high-density velocity analysis shows that velocity anomalies (>2000 m/s) are found on the northeastern side of the turbidite channels. The depositional stage of the northeastern side of the turbidite channels exhibits slightly older sediment stages than the depositional stages of the remaining channels. Hence, the velocity anomalies of the northeastern side of the channels are related to the different stages of sediment supply, and this may lead to the different reservoir architectures of the turbidite channels. © 2011 Elsevier Ltd.

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.

Lokier S.,Petroleum Institute | Onuma T.,JGI Inc.
EAGE/GRSG Remote Sensing Workshop | Year: 2012

Low-angle ramp geometry of the Abu Dhabi coastline offers an ideal setting for studying the effects of relative sea-level fluctuations on shoreline sedimentary systems and geomorphology. A late Holocene progradation rate of 0.75m/yr has been established for the Abu Dhabi sabkha system, however, a present marine transgression rate at the coastline is estimated to be 8.25m/yr based on current global sea level rise of 3.3mm/yr, it is therefore inferred that the area has entered a broadly retrogradational phase. The study utilised very high spatial resolution satellite images acquired in 2003, 2004, 2005, 2007, and 2010. They were used to trace temporal morphological changes along the coastline. Through the comparison of satellite images spits and beach ridge systems in the western part of the study area have been recognized to advance landward, over a distance of up to 207 m during a 7.5 year period. In the eastern part a landward migration of intertidal deltas has been established, and significant erosion of the upper intertidal microbial mat belt has also been proved. When combined with 7 years of fieldwork observations, these results indicate that the current sedimentary regime is broadly regressive associated with current marine transgression of the sabkha system.

Ali M.Y.,Petroleum Institute | Onuma T.,JGI Inc.
EAGE/GRSG Remote Sensing Workshop | Year: 2012

Popular public domain DEM includes Shuttle Radar Topography Mission (SRTM) with 3 arcsec grid and Terra ASTER GDEM with 1 arcsec grid, which can provide with fundamental topographic information. Finer grid DEM than ASTER GDEM may be required in some researches, but cloud-free stereo pairs of optical sensor images with very fine spatial resolution may be needed to create such fine DEM, and such satellite image data is usually costly. An alternative practical method of DEM calculation is SAR interferometry using satellite SAR data. The study shows an example of DEM calculation using ALOS PALSAR data (PALSAR DEM) for a mountainous area in UAE and Oman, and quality assessment of the DEM through comparison with SRTM and ASTER GDEM as well as field GPS data. Several ALOS PALSAR interferometry pairs with appropriate parameters for DEM calculation were selected, and calculated DEMs were stacked to decrease the effect of phase noise and to create 10 m/pixel grid DEM. By using 10m grid PALSAR DEM for terrain correction, detail complete gravity anomaly was obtained in northwestern Oman Mountains.

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