Strength and deformation behavior of the Shimanto accretionary complex across the Nobeoka thrust          下载免费PDF全文

Hiroko Kitajima  Miki Takahashi  Makoto Otsubo  Demian Saffer  Gaku Kimura 《Island Arc》2017,26(4)

A rapid reduction in sediment porosity from 60 to 70 % at seafloor to less than 10 % at several kilometers depth can play an important role in deformation and seismicity in the shallow portion of subduction zones. We conducted deformation experiments on rocks from an ancient accretionary complex, the Shimanto Belt, across the Nobeoka Thrust to understand the deformation behaviors of rocks along plate boundary faults at seismogenic depth. Our experimental results for phyllites in the hanging wall and shale‐tuff mélanges in the footwall of the Nobeoka Thrust indicate that the Shimanto Belt rocks fail brittlely accompanied by a stress drop at effective pressures < 80 MPa, whereas they exhibit strain hardening at higher effective pressures. The transition from brittle to ductile behavior in the shale–tuff mélanges lies on the same trend in effective stress–porosity space as that for clay‐rich and tuffaceous sediments subducting into the modern Nankai subduction zone. Both the absolute yield strength and the effective pressure at the brittle–ductile transition for the phyllosilicate‐rich materials are much lower than for sandstones. These results suggest that as the clay‐rich or tuffaceous sediments subduct and their porosities are reduced, their deformation behavior gradually transitions from ductile to brittle and their yield strength increases. Our results also suggest that samples of the ancient Shimanto accretionary prism can serve as an analog for underthrust rocks at seismogenic depth in the modern Nankai Trough.  相似文献   

Dynamic FE simulation of four‐story steel frame modeled by solid elements and its validation using results of full‐scale shake‐table test          下载免费PDF全文

Tomoshi Miyamura  Takuzo Yamashita  Hiroshi Akiba  Makoto Ohsaki 《地震工程与结构动力学》2015,44(9):1449-1469

Dynamic finite element analyses of a four‐story steel building frame modeled as a fine mesh of solid elements are performed using E‐Simulator, which is a parallel finite element analysis software package for precisely simulating collapse behaviors of civil and building structures. E‐Simulator is under development at the National Research Institute for Earth Science and Disaster Prevention (NIED), Japan. A full‐scale shake‐table test for a four‐story frame was conducted using E‐Defense at NIED, which is the largest shaking table in the world. A mesh of the entire structure of a four‐story frame with approximately 19 million degrees of freedom is constructed using solid elements. The density of the mesh is determined by referring to the results of elastic–plastic buckling analyses of a column of the frame using meshes of different densities. Therefore, the analysis model of the frame is well verified. Seismic response analyses under 60, 100, and 115% excitations of the JR Takatori record of the 1995 Hyogoken‐Nanbu earthquake are performed. Note that the simulation does not reproduce the collapse under the 100% excitation of the Takatori record in the E‐Defense test. Therefore, simulations for the 115% case are also performed. The results obtained by E‐Simulator are compared with those obtained by the E‐Defense full‐scale test in order to validate the results obtained by E‐Simulator. The shear forces and interstory drift angles of the first story obtained by the simulation and the test are in good agreement. Both the response of the entire frame and the local deformation as a result of elastic–plastic buckling are simulated simultaneously using E‐Simulator. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

Finite‐element analysis of laminated rubber bearing of building frame under seismic excitation          下载免费PDF全文

Makoto Ohsaki  Tomoshi Miyamura  Masayuki Kohiyama  Takuzo Yamashita  Masashi Yamamoto  Naohiro Nakamura 《地震工程与结构动力学》2015,44(11):1881-1898

Finite element analysis is carried out for a building frame supported by laminated rubber bearings to simultaneously investigate global displacement and local stress responses under seismic excitation. The frame members and the rubber bearings are discretized into hexahedral solid elements with more than 3 million degrees of freedom. The material property of rubber is represented by the Ogden model, and the frame is assumed to remain in elastic range. It is shown that the time histories of non‐uniform stress distribution and rocking behavior of the rubber bearings under a frame subjected to seismic excitation can be successfully evaluated, and detailed responses of base and frame can be evaluated through large‐scale finite element analysis. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Atmospheric gravity waves identified by ground-based observations of the intensity and rotational temperature of OH airglow     

Hidehiko Suzuki  Kazuo Shiokawa  Masaki Tsutsumi  Takuji Nakamura  Makoto Taguchi 《Polar Science》2008,2(1):1-8

Spectroscopic observations of OH airglow undertaken on May 2, 2006 at Uji, Japan reveal variations in intensity and rotational temperature related to the passage of an atmospheric gravity wave. The variations exhibit a period of approximately 1 h and magnitudes of 2–6% in intensity and 0.5–2% in rotational temperature. The vertical wavelength and intrinsic frequency of the atmospheric gravity wave were determined from the horizontal wavelength derived by an OH airglow imager, the background horizontal wind velocity obtained by the middle and upper atmosphere (MU) radar, and the dispersion relationship. The observed variations are consistent with the values calculated using the model of Liu, A.Z., Swenson, G.R. [2003. A modeling study of O₂ and OH airglow perturbations induced by atmospheric gravity waves. J. Geophys. Res. 108 (No. D4), 4151. doi:10.1029/2002JD002474].  相似文献   

Simple relationship between seismic activity along Philippine Sea slab and geometry of oceanic Moho beneath southwest Japan   总被引：4，自引：0，他引：4  

Katsuhiko Shiomi  Makoto Matsubara  Yoshihiro Ito  Kazushige Obara 《Geophysical Journal International》2008,173(3):1018-1029

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SAR- and gravity change-based characterization of the distribution pattern of pyroclastic flow deposits at Mt. Merapi during the past 10 years     

Asep Saepuloh  Katsuaki Koike  Makoto Omura  Masato Iguchi  Ari Setiawan 《Bulletin of Volcanology》2010,72(2):221-232

Mt. Merapi, Indonesia, is one of the most active and dangerous volcanoes in the Torrid Zone. This volcano has erupted frequently and has produced pyroclastic flows following the collapse of the summit lava dome. We used Synthetic Aperture Radar (SAR) data acquired by JERS-1 and RADARSAT-1 satellites from April 1996 to July 2006 to clarify the distribution patterns of the pyroclastic flow deposits. The extent of the deposits, termed P-zones, was accurately extracted by ratio operation and low-level feature extraction from SAR intensity images. These images highlighted temporal changes of the distribution area, perimeter, flow distance, included angle, and collapse direction. To validate the image-processing results, reflectance spectra of the rock samples collected after the eruption in June 2006 were measured in a laboratory. The reflectance spectra of all samples showed similar characteristics to the reference spectra, which were derived from atmospheric correction of Hyperion sensor image data covering the lava dome at the summit. Therefore, P-zones were confirmed to be the pyroclastic flow deposits originating from destruction of the lava dome at the summit. The image-processing results clarified that the extent of the distribution areas, perimeter, flow distances, and included angle of the P-zones were variable among the eruptions, while the collapse direction had a constant pattern. The collapse pattern followed a clockwise change from the south toward the west. By comparing the ratio maps of Bouguer gravity anomaly data in two periods, the change was interpreted to originate from the inclination of the conduit and the formation of shallow and deep magma reservoirs.  相似文献   

Temporal variations in channel patterns and facies architecture in a gravelly fluvial system: The Paleogene Iwaki Formation on the Joban Coalfield,a forearc basin in Northeast Japan     

Kenichiro Shibata  Makoto Ito  Nagayuki Nemoto  Sakae O'Hara 《Island Arc》2010,19(3):489-505

This paper examined sequence‐stratigraphic features of a gravelly fluvial system of the Iwaki Formation, which developed in a forearc‐basin setting in Northeast Japan during the Eocene through Oligocene. On the basis of three‐dimensional architectural element analysis, we discriminated three major cycles of channel complexes, which contain ten component channel deposits in total in the fluvial succession. Component channel deposits in the uppermost part of each cycle are sandier and associated with overbank muddy deposits and coal beds as compared with those in the lower part of the cycle. Mean clast‐size also decreases upsection in the entire gravelly fluvial deposits. The fluvial succession is interpreted to have been deposited in response to an overall rise in relative sea level that was superimposed by three short‐term relative sea‐level rises on the basis of vertical stacking patterns and component lithofacies features of channel deposits, and of correlation of the fluvial succession with an age‐equivalent marine succession in an area about 50 km offshore. However, geometry and stacking patterns of the channel complexes do not exhibit any distinct temporal variation and amalgamated channel and bar deposits are dominant throughout the transgressive fluvial succession. On the other hand, an overall fining‐upward pattern of the entire Iwaki Formation fluvial deposits in association with three component fining‐upward patterns is distinct, and is interpreted to be consistent with the tenet of the standard fluvial sequence‐stratigraphic models. This indicates that the present example represents one type of variation in the standard fluvial sequence‐stratigraphic models, possibly reflecting the forearc‐basin setting, which is generally represented by higher valley slope, higher shedding of coarse‐grained sediments, and shorter longitudinal profiles to the coastal area as compared with a passive‐continental‐margin setting.  相似文献   

Mixing of magmatic CO₂ into volcano groundwater flow at Aso volcano assessed combining carbon and water stable isotopes     

Makoto Yamada  Shinji Ohsawa  Kohei Kazahaya  Masaya Yasuhara  Hiroshi Takahashi  Kazuhiro Amita  Hideo Mawatari  Shin Yoshikawa 《Journal of Geochemical Exploration》2011

To understand deep groundwater flow systems and their interaction with CO₂ emanated from magma at depth in a volcanic edifice, deep groundwater samples were collected from hot spring wells in the Aso volcanic area for hydrogen, oxygen and carbon isotope analyses and measurements of the stable carbon isotope ratios and concentrations of dissolved inorganic carbon (DIC). Relations between the stable carbon isotope ratio (δ¹³C_DIC) and DIC concentrations of the sampled waters show that magma-derived CO₂ mixed into the deep groundwater. Furthermore, groundwaters of deeper areas, except samples from fumarolic areas, show higher δ¹³C_DIC values. The waters' stable hydrogen and oxygen isotope ratios (δD and δ¹⁸O) reflect the meteoric-water origin of that region's deep groundwater. A negative correlation was found between the altitude of the well bottom and the altitude of groundwater recharge as calculated using the equation of the recharge-water line and δD value. This applies especially in the Aso-dani area, where deeper groundwater correlates with higher recharge. Groundwater recharged at high altitude has higher δ¹³C_DIC of than groundwater recharged at low altitude, strongly suggesting that magmatic CO₂ is present to a much greater degree in deeper groundwater. These results indicate that magmatic CO₂ mixes into deeper groundwater flowing nearer the magma conduit or chamber.  相似文献   

Biogenic carbon flows through the planktonic food web of the Amundsen Gulf (Arctic Ocean): A synthesis of field measurements and inverse modeling analyses   总被引：1，自引：0，他引：1  

Alexandre Forest  Jean-Éric Tremblay  Yves Gratton  Johannie Martin  Jonathan Gagnon  Gérald Darnis  Makoto Sampei  Louis Fortier  Mathieu Ardyna  Michel Gosselin  Hiroshi Hattori  Dan Nguyen  Roxane Maranger  Dolors Vaqué  Cèlia Marrasé  Carlos Pedrós-Alió  Amélie Sallon  Christine Michel  Colleen Kellogg  Jody Deming  Elizabeth Shadwick  Helmuth Thomas  Heike Link  Philippe Archambault  Dieter Piepenburg 《Progress in Oceanography》2011,91(4):410-436

Major pathways of biogenic carbon (C) flow are resolved for the planktonic food web of the flaw lead polynya system of the Amundsen Gulf (southeast Beaufort Sea, Arctic Ocean) in spring-summer 2008. This period was relevant to study the effect of climate change on Arctic marine ecosystems as it was characterized by unusually low ice cover and warm sea surface temperature. Our synthesis relied on a mass balance estimate of gross primary production (GPP) of 52.5 ± 12.5 g C m⁻² calculated using the drawdown of nitrate and dissolved inorganic C, and a seasonal f-ratio of 0.64. Based on chlorophyll a biomass, we estimated that GPP was dominated by phytoplankton (93.6%) over ice algae (6.4%) and by large cells (>5 μm, 67.6%) over small cells (<5 μm, 32.4%). Ancillary in situ data on bacterial production, zooplankton biomass and respiration, herbivory, bacterivory, vertical particle fluxes, pools of particulate and dissolved organic carbon (POC, DOC), net community production (NCP), as well as selected variables from the literature were used to evaluate the fate of size-fractionated GPP in the ecosystem. The structure and functioning of the planktonic food web was elucidated through inverse analysis using the mean GPP and the 95% confidence limits of every other field measurement as lower and upper constraints. The model computed a net primary production of 49.2 g C m⁻², which was directly channeled toward dominant calanoid copepods (i.e. Calanus hyperboreus 20%, Calanus glacialis 10%, and Metridia longa 10%), other mesozooplankton (12%), microzooplankton (14%), detrital POC (18%), and DOC (16%). Bacteria required 29.9 g C m⁻², a demand met entirely by the DOC derived from local biological activities. The ultimate C outflow comprised respiration fluxes (82% of the initial GPP), a small sedimentation (3%), and a modest residual C flow (15%) resulting from NCP, dilution and accumulation. The sinking C flux at the model limit depth (395 m) supplied 60% of the estimated benthic C demand (2.8 g C m⁻²), suggesting that the benthos relied partly on other C sources within the bottom boundary layer to fuel its activity. In summary, our results illustrate that the ongoing decline in Arctic sea ice promotes the growth of pelagic communities in the Amundsen Gulf, which benefited from a ∼80% increase in GPP in spring-summer 2008 when compared to 2004 – a year of average ice conditions and relatively low GPP. However, 53% of the secondary production was generated within the microbial food web, the net ecological efficiency of zooplankton populations was not particularly high (13.4%), and the quantity of biogenic C available for trophic export remained low (6.6 g C m⁻²). Hence it is unlikely that the increase in lower food web productivity, such as the one observed in our study, could support new harvestable fishery resources in the offshore Beaufort Sea domain.  相似文献   

Paleomagnetism of the Middle–Late Jurassic to Cretaceous red beds from the Peninsular Thailand: Implications for collision tectonics     

Itaru Yamashita  Adichat Surinkum  Yutaka Wada  Makoto Fujihara  Masao Yokoyama  Haider Zaman  Yo-ichiro Otofuji 《Journal of Asian Earth Sciences》2011,40(3):784-796

Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination (D = 31.1°, I = 12.2°, α₉₅ = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination (D = 342.8°, I = 22.3°, α₉₅ = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin.  相似文献