Application of common reflection angle migration for imaging deformation structures in an inner accretionary wedge,Nankai Trough,Japan     

Kazuya Shiraishi  Masako Robb  Karl Hosgood  Yasuhiro Yamada 《Geophysical Prospecting》2019,67(2):317-330

To better image deformation structures within the inner accretionary wedge of the Nankai Trough, Japan, we apply common reflection angle migration to a legacy two-dimensional seismic data set acquired with a 6 km streamer cable. In this region, many seismic surveys have been conducted to study the seismogenic zone related to plate subduction. However, the details of the accreted sediments beneath the Kumano forearc basin are still unclear due to the poor quality of seismic images caused by multiple reflections, highly attenuated signals, and possibly complex geological structures. Generating common image gathers in the subsurface local angle domain rather than the surface offset domain is more advantageous for imaging geological structures that involve complex wave paths and poor illumination. By applying this method, previously unseen structures are revealed in the thick accreted sediments. The newly imaged geometric features of reflectors, such as the folds in the shallow part of the section and the deep reflectors with stepwise discontinuities, imply deformation structures with multiple thrust faults. The reflections within the deep accreted sediments (approximately 5 km) are mainly mapped to far angles (30°–50°) in the common reflection angles, which correspond to the recorded offset distances greater than 4.5 km. This result indicates that the far offset/angle information is critical to image the deformation structures at depth. The new depth image from the common reflection angle migration provides seismic evidence of multiple thrust faults and their relationship with the megathrust fault that is essential for understanding the structure and evolution of the Nankai Trough seismogenic zone.  相似文献   

Nutrients,light and phytoplankton production in the shallow,tropical coastal waters of Bandon Bay,Southern Thailand          下载免费PDF全文

Takashi Yoshikawa  Kosuke Tomizawa  Yuki Okamoto  Kazuya Watanabe  Jintana Salaenoi  Kenichi Hayashizaki  Hisashi Kurokura  Satoshi Ishikawa 《Marine Ecology》2017,38(6)

Phytoplankton primary production and its regulation by light and nutrient availability were investigated in the shallow, tropical coastal waters of Bandon Bay, Southern Thailand. The bay was meso‐eutrophicated and highly turbid, receiving river water discharge. Water column stratification was consistently weak during both rainy and dry seasons. Dissolved inorganic nitrogen (DIN) was higher off the river mouth than in the other regions, suggesting that river water discharge was a main source of DIN. By contrast, dissolved inorganic phosphorus (DIP) showed a significant negative correlation with total water depth, implying that regeneration around the sea floor was an important source of DIP. Surface DIN and DIP showed positive correlations with surface primary production (PP) and water column primary productivity (ΣPP*), respectively. The combined correlation and model analyses indicate that total water depth had an ambivalent influence on water column primary production (ΣPP); shallower water depth induced more active regeneration of nutrients, but it also caused higher turbidity and lower light availability as a result of enhanced resuspension of sediments. Furthermore, there was a vertical constraint for phytoplankton during the rainy season: total water depth tended to be shallower than euphotic zone depth. In conclusion, light limitation and vertical constraint owing to shallow water depth appear to be more important than nutrient limitation for water column primary production in Bandon Bay.  相似文献   

Three-Dimensional Subsurface Structure Model of Kansai International Airport by Integration of Borehole Data and Seismic Profiles     

Naoto Inoue  Naoko Kitada  Keiji Takemura  Koji Fukuda  Tsuyoshi Emura 《Geotechnical and Geological Engineering》2013,31(3):881-890

The three-dimensional subsurface structure model around Kansai International Airport (KIX) has been developed based on the geologically and geotechnically investigated results of a large amount of borehole data for estimation of subsidence. The model consists of the alternation of marine clay and coarse deposits. The many seismic surveys and borehole drillings were carried out around the KIX before the constructing the airport. The stratigraphy of the model was renewed by the KIX18-1, which was about 1,300 m long drilling core and was drilled near the 2nd runway of the KIX from 2006 to 2007. In this study, the subsurface geological model was revised by integration of renewed borehole data and seismic profiles to incorporate complex warping structure and heterogenic lateral variation.  相似文献   

An East-West Comparison of the Transition Zone Coastal Pelagic Nekton of the North Pacific Ocean     

Richard D. Brodeur  Joseph P. Fisher  Yasuhiro Ueno  Kazuya Nagasawa  William G. Pearcy 《Journal of Oceanography》2003,59(4):415-434

During the 1980s and 1990s, scientific research cruises were conducted in both the eastern and western boundary regions of the North Pacific Ocean. The main purpose of these cruises was to examine the abundance and distribution patterns of juvenile salmon in coastal waters. These studies created one of the most extensive databases ever collected on the species composition of coastal Transition Zone epipelagic nekton in the North Pacific Ocean. Catch data from two purse seine and two surface trawl surveys (one each from off northern Japan and eastern Russia and off the West Coast of the U.S.) were examined using multivariate techniques to analyze the community structure of nektonic cephalopods, elasmobranchs, and teleosts in the coastal zone during the summer and autumn months. Juvenile salmonids are generally among the most common species caught, but in terms of overall abundance, other potential competitors with juvenile salmon, such as small squids and clupeoid fishes predominated the catches. Species diversity and dominance varied among areas and gear types. Distinct assemblages were found in each area, but the two regions had closely related species occupying similar ecological positions in each habitat. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Spatial Variability of Living Coccolithophore Distribution in the Western Subarctic Pacific and Western Bering Sea   总被引：1，自引：0，他引：1  

Hiroshi Hattori  Makoto Koike  Kenichi Tachikawa  Hiroaki Saito  Kazuya Nagasawa 《Journal of Oceanography》2004,60(2):505-515

Vertical distributions of coccolithophores were observed in the depth range 0–50 m in the western subarctic Pacific and western Bering Sea in summer, 1997. Thirty-five species of coccolithophores were collected. Overall, Emiliania huxleyi var. huxleyi was the most abundant taxon, accounting for 82.8% of all coccolithophores, although it was less abundant in the western Bering Sea. Maximum abundance of this species was found in an area south of 41°N and east of 175°E (Transition Zone) reaching >10,000 cells L⁻¹ in the water column. In addition to this species, Coccolithus pelagicus f. pelagicus, which accounted for 4.2% of the assemblage, was representative of the coccolithophore standing crop in the western part of the subarctic Pacific. Coccolithus pelagicus f. hyalinus was relatively abundant in the Bering Sea, accounting for 2.6% of the assemblage. Coccolithophore standing crops in the top 50 m were high south of 41°N (>241 × 10⁶ cells m⁻²) and east of 170°E (542 × 10⁶ cells m⁻²) where temperatures were higher than 12°C and salinities were greater than 34.2. The lowest standing crop was observed in the Bering Sea and Oyashio areas where temperatures were lower than 6–10°C and salinities were less than 33.0. From the coccolithophore volumes, the calcite stocks in the Transition, Subarctic, and the Bering Sea regions were estimated to be 73.0, 9.7, and 6.9 mg m⁻², respectively, corresponding to calcite fluxes of 3.6, 0.5, and 0.3 mg m⁻²d⁻¹ using Stoke's Law. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Determination of the oxidation state of radiogenic Pb in natural zircon using X-ray absorption near-edge structure     

Kazuya Tanaka  Yoshio Takahashi  Kenji Horie  Hiroshi Shimizu  Takashi Murakami 《Physics and Chemistry of Minerals》2010,37(4):249-254

We examined the L_III-edge Pb X-ray absorption near-edge structure (XANES) of three natural zircon samples with different amounts of radiation doses (1.9 × 10¹⁵ to 6.8 × 10¹⁵ α-decay events/mg). The results suggest that the oxidation state of radiogenic Pb in the zircon sample with the highest radiation dose is divalent. The XANES spectra of the two other samples with lower radiation doses suggest that radiogenic Pb(II) is present, and further that some Pb may be tetravalent. This is the first work on the determination of the oxidation state of radiogenic Pb in natural zircon using XANES.  相似文献   

The 1966 Kremasta reservoir earthquake sequence     

Seth Stein  Douglas A. Wiens  Kazuya Fujita 《Earth and Planetary Science Letters》1982,59(1):49-60

  相似文献   

Trace element characteristics of the fluid liberated from amphibolite-facies slab: Inference from the metamorphic sole beneath the Oman ophiolite and implication for boninite genesis   总被引：3，自引：0，他引：3  

Tsuyoshi Ishikawa  Shiori Fujisawa  Kazuya Nagaishi  Toshiaki Masuda 《Earth and Planetary Science Letters》2005,240(2):355-377

Major and trace element compositions of amphibolites and quartzose rocks in the 230-m-thick metamorphic sole underlying the mantle section of the Oman ophiolite in Wadi Tayin area were determined to investigate the chemical characteristics of the hydrous fluid released from subducted amphiboltie-facies slab. The fluid-immobile element compositions indicate that protoliths of these rocks are mid-ocean ridge basalt-like tholeiite and deep-sea chert, which is consistent with the idea that these rocks represent Tethyan oceanic crust overridden during the early, intraoceanic thrusting stage of the Oman ophiolite emplacement. The rare-earth element (REE) and high field-strength element concentrations of the amphibolites show limited variations, within a factor of two except for a few evolved samples, throughout transect of the sole. On the other hand, concentrations of fluid-mobile elements, especially B, Rb, K and Ba, in amphibolites are highly elevated in upper 30 m of the sole (> 600 °C in peak metamorphic temperature), suggesting the equilibration with evolved, B-Rb-K-Ba-rich fluids during prograde metamorphism. The comparison with amphibolites in the lower 150 m (500 to 550 °C) demonstrates that the trace element spectra of the fluids equilibrated with the high-level amphibolites may vary as a function of metamorphic temperature. The fluids are characterized by striking enrichments of B, Rb, K and Ba and moderate to minor enrichments of Sr, Li, Be and Pb. At higher temperature (up to 700 °C), the fluids become considerably enriched in light REE and Nb in addition to the above elements. The estimated trace element spectra of the fluids do not coincide with the compositions of basalts from matured intra-oceanic arcs, but satisfactorily explain the characteristics of the low-Pb andesites and boninites found in the Oman ophiolite. Compositional similarity between the boninites of Oman and other localities suggests that the fluids estimated here well represent the amphibolite-derived fluids involved in the magmatism of immatured, hot, shallow subduction zones.  相似文献   

A web-based real-time and full-resolution data visualization for Himawari-8 satellite sensed images     

Ken T. Murata  Praphan Pavarangkoon  Atsushi Higuchi  Koichi Toyoshima  Kazunori Yamamoto  Kazuya Muranaga  Yoshiaki Nagaya  Yasushi Izumikawa  Eizen Kimura  Takamichi Mizuhara 《Earth Science Informatics》2018,11(2):217-237

It has been almost four decades since the first launch of geostationary meteorological satellite by Japan Meteorological Agency (JMA). The specifications of the geostationary meteorological satellites have shown tremendous progresses along with the generations, which are now entering their third generation. The third-generation geostationary meteorological satellites not only yield basic data for weather monitoring, but also globally observe the Earth’s environment. The development of multi-band imagers with improved spatial resolution onboard the third-generation geostationary meteorological satellites brings us meteorological data in larger size than those of the second-generation ones. Thus, new techniques for domestic and world-wide dissemination of the observational big data are needed. In this paper, we develop a web-based data visualization for Himawari-8 satellite sensed images in real time and with full resolution. This data visualization is supported by the ecosystems, which uses a tiled pyramid representation and parallel processing technique for terrain on an academic cloud system. We evaluate the performance of our techniques for domestic and international users on laboratory experiments. The results show that our data visualization is suitable for practical use on a temporal preview of observation image data for the domestic users.  相似文献   

Zircon U–Pb ages of plutonic rocks in the southern Abukuma Mountains: Implications for Cretaceous geotectonic evolution of the Abukuma Belt          下载免费PDF全文

Yutaka Takahashi  Masumi Mikoshiba  Kazuya Kubo  Hideki Iwano  Tohru Danhara  Takafumi Hirata 《Island Arc》2016,25(2):154-188

Plutonic rocks in the southern Abukuma Mountains include gabbro and diorite, fine‐grained diorite, hornblende–biotite granodiorite (Ishikawa, Samegawa, main part of Miyamoto and Tabito, Kamikimita and Irishiken Plutons), biotite granodiorite (the main part of Hanawa Pluton and the Torisone Pluton), medium‐ to coarse‐grained biotite granodiorite and leucogranite, based on the lithologies and geological relations. Zircon U–Pb ages of gabbroic rocks are 112.4 ±1.0 Ma (hornblende gabbro, Miyamoto Pluton), 109.0 ±1.1 Ma (hornblende gabbro, the Hanawa Pluton), 102.7 ±0.8 Ma (gabbronorite, Tabito Pluton) and 101.0 ±0.6 Ma (fine‐grained diorite). As for the hornblende–biotite granodiorite, zircon U–Pb ages are 104.2 ±0.7 Ma (Ishikawa Pluton), 112.6 ±1.0 Ma (Tabito Pluton), 105.2 ±0.8 Ma (Kamikimita Pluton) and 105.3±0.8 Ma (Irishiken Pluton). Also for the medium‐ to fine‐grained biotite granodiorite, zircon U–Pb ages are 106.5±0.9 Ma (Miyamoto Pluton), 105.1 ±1.0 Ma (Hanawa Pluton) and the medium‐ to coarse‐grained biotite granodiorite has zircon U–Pb age of 104.5 ±0.8 Ma. In the case of the leucogranite, U–Pb age of zircon is 100.6 ±0.9 Ma. These data indicate that the intrusion ages of gabbroic rocks and surrounding granitic rocks ranges from 113 to 101 Ma. Furthermore, K–Ar ages of biotite and or hornblende in the same rock samples were dated. Accordingly, it is clear that these rocks cooled down rapidly to 300 °C (Ar blocking temperature of biotite for K–Ar system) after their intrusion. These chronological data suggest that the Abukuma plutonic rocks in the southern Abukuma Mountains region uplifted rapidly around 107 to 100 Ma after their intrusion.  相似文献