Sequential high-pressure transformations of FeGeO3 high-P clinopyroxene (C 2 /c) at temperatures up to 365 ¯C     

T. Hattori  T. Tsuchiya  T. Nagai  T. Yamanaka 《Physics and Chemistry of Minerals》2001,28(6):377-387

 In order to elucidate high-pressure transformations of high-P clinopyroxene (C2/c) at kinetically low temperature where atoms are not thermally activated, the transformation processes of FeGeO₃ clinopyroxene (C2/c) have been investigated at pressures up to 20 GPa and 365 °C by powder X-ray diffraction using a synchrotron radiation source and TEM observation. With increasing pressure up to 20 GPa at room temperature, FeGeO₃ high-P clinopyroxene (C2/c) reversibly transforms into a new high-pressure phase, FeGeO₃(II). On increasing the temperature up to 365 °C, this phase rapidly transforms into FeGeO₃ ilmenite within about 2 h. Intensity analysis of the X-ray diffraction pattern reveals that the high-pressure phase of FeGeO₃(II) has an intermediate structure between clinopyroxene and ilmenite: the cation arrangement is similar to that of clinopyroxene and the oxygen arrangement is similar to that of ilmenite. The comparison of the crystal structures of these polymorphs suggests that clinopyroxene to FeGeO₃(II) and FeGeO₃(II) to ilmenite transformations are performed by the slight deformation of the oxygen packing and the short-range movement of cations, respectively. It is shown that this high-P clinopyroxene transforms into ilmenite through a low-activation energy path under the low-temperature condition. Received: 30 August 2000 / Accepted: 10 February 2001  相似文献   

Three-dimensional P-wave velocity structure beneath the Indonesian region     

Nanang T. Puspito  Yoshiko Yamanaka  Takashi Miyatake  Kunihiko Shimazaki  Kazuro Hirahara 《Tectonophysics》1993,220(1-4):175-192

We present the P-wave seismic tomography image of the mantle to a depth of 1200 km beneath the Indonesian region. The inversion method is applied to a dataset of 118,203 P-wave travel times of local and teleseismic events taken from ISC bulletins. Although the resolution is sufficient for detailed discussion in only a limited part of the study region, the results clarify the general tectonic framework in this region and indicate a possible remnant seismic slab in the lower mantle.

Structures beneath the Philippine Islands and the Molucca Sea region are well resolved and high-velocity zones corresponding to the slabs of the Molucca Sea and Philippine Sea plates are well delineated. Seismic zones beneath the Manila, Negros and Cotabato trenches are characterized by high-velocity anomalies, although shallow structures were not resolved. The Molucca Sea collision zone and volcanic zones of the Sangihe and Philippine arcs are dominated by low-velocity anomalies. The Philippine Sea slab subducts beneath the Philippine Islands at least to a depth of 200 km and may reach depths of 450 km. The southern end of the slab extends at least to about 6°N near southern Mindanao. In the south, the two opposing subducting slabs of the Molucca Sea plate are clearly defined by the two opposing high-velocity zones. The eastward dipping slab can be traced about 400 km beneath the Halmahera arc and may extend as far north as about 5°N. Unfortunately, resolution is not sufficient to reveal detailed structures at the boundary region between the Halmahera and Philippine Sea slabs. The westward dipping slab may subduct to the lower mantle although its extent at depth is not well resolved. This slab trends N-S from about 10°N in the Philippine Islands to northern Sulawesi. A NE-SW-trending high-velocity zone is found in the lower mantle beneath the Molucca Sea region. This high-velocity zone may represent a remnant of the former subduction zone which formed the Sulawesi arc during the Miocene.

The blocks along the Sunda and Banda arcs are less well resolved than those in the Philippine Islands and the Molucca Sea region. Nevertheless, overall structures can be inferred. The bowl-shaped distribution of the seismicity of the Banda arc is clearly defined by a horseshoe-shaped high-velocity zone. The tomographic image shows that the Indian oceanic slab subducts to a depth deeper than 300 km i.e., deeper than its seismicity, beneath Andaman Islands and Sumatra and may be discontinuous in northern Sumatra. Along southern Sumatra, Java and the islands to the east, the slab appears to be continuous and can be traced down to at least a depth of the deepest seismicity, where it appears to penetrate into the lower mantle.  相似文献   

Three-year investigations into sperm whale-fall ecosystems in Japan   总被引：2，自引：0，他引：2  

Yoshihiro Fujiwara  Masaru Kawato  Tomoko Yamamoto  Toshiro Yamanaka  Waka Sato-Okoshi  Chikayo Noda  Shinji Tsuchida  Tomoyuki Komai  Sherine Sonia Cubelio  Takenori Sasaki  Karen Jacobsen  Kaoru Kubokawa  Katsunori Fujikura  Tadashi Maruyama  Yasuo Furushima  Kenji Okoshi  Hiroshi Miyake  Masayuki Miyazaki  Yuichi Nogi  Akiko Yatabe  & Takashi Okutani 《Marine Ecology》2007,28(1):219-232

We report the first study of sperm whale‐fall ecosystems, based on mass sinking of whale carcasses at shelf depths in the northwest Pacific. We conducted three observations over a 2‐year period on replicate sperm‐whale carcasses implanted at depths of 219–254 m off the southern part of Japan from July 2003 to August 2005. The study was made possible by a mass stranding of sperm whales in January 2002, and the subsequent sinking of 12 carcasses in the waters off Cape Nomamisaki. Dense aggregations of unique chemosynthesis‐based fauna had formed around the whale carcasses after 18 months (July 2003). The mytilid mussel Adipicola pacifica was the most abundant macrofaunal species and covered most of the exposed bone surfaces. The general composition of the fauna was similar to that of deep‐water reducing habitats, but none of the species appearing in this study has been found at hydrothermal vents, cold seeps or deep‐water whale falls. A new species of lancelet, which was the first record of the subphylum Cephalochordata from reducing environments, a new species of Osedax; a rarely encountered benthic ctenophore, and a rare gastropod species were discovered at this sperm whale‐fall site. Benthic communities were similar across all the carcasses studied, although the body sizes of the whales were very different. The succession of epifaunal communities was relatively rapid and the sulphophilic stage was considerably shorter than that of other known whale falls.  相似文献   

Correction to: Microtremor array method using spatial autocorrelation analysis of Rayleigh-wave data     

Hayashi  Koichi  Asten  Michael W.  Stephenson  William J.  Cornou  Cécile  Hobiger  Manuel  Pilz  Marco  Yamanaka  Hiroaki 《Journal of Seismology》2022,26(4):629-629

Journal of Seismology -  相似文献   

Microtremor array method using spatial autocorrelation analysis of Rayleigh-wave data     

Hayashi  Koichi  Asten  Michael W.  Stephenson  William J.  Cornou  Cécile  Hobiger  Manuel  Pilz  Marco  Yamanaka  Hiroaki 《Journal of Seismology》2022,26(4):601-627

Journal of Seismology - Microtremor array measurements, and passive surface wave methods in general, have been increasingly used to non-invasively estimate shear-wave velocity structures for...  相似文献   

Broadband ground-motion simulation of the 24 May 2014 Gokceada (North Aegean Sea) earthquake (Mw 6.9) in NW Turkey considering local soil effects     

Ozlem Karagoz  Kosuke Chimoto  Hiroaki Yamanaka  Oguz Ozel  Seckin Citak 《Bulletin of Earthquake Engineering》2018,16(1):23-43

On 24 May 2014, a Mw 6.9 earthquake occurred in the west of Gokceada Island, northern Aegean Sea. The earthquake was close to Canakkale, Enez, Tekirdag cities, and damaged 300 buildings in the Marmara Region, NW Turkey. We simulated its broadband (0.1–10 Hz) ground motions including 1D deep and shallow structures soil amplification effects at the 12 strong ground motion stations in the western Marmara Region. The 1D deep velocity structures from the focal layer to the engineering bedrock with an S-wave velocity of 0.78 km/s in different azimuthal directions were tuned by comparing the observed group-velocity dispersion curves of Rayleigh and Love waves from the mainshock with theoretical ones. We also added the shallow parts from previous surveys into the 1D models. Synthetic seismograms on the engineering bedrock were generated using the discrete wave number method with a source model and the 1D deep velocity structures. Then the surface motion was generated considering shallow soil amplification. The synthetic seismograms are generally in good agreement with the observed low and high-frequency parts at most of the stations indicating an appropriateness of the source model and the 1D structural model.  相似文献   

Exploration of S-wave velocity profiles at strong motion stations in Eskisehir,Turkey, using microtremor phase velocity and S-wave amplification     

Hiroaki Yamanaka  Ögur Tuna Özmen  Kosuke Chimoto  Mehmet Akif Alkan  Muammer Tün  Emrah Pekkan  Oguz Özel  Derya Polat  Murat Nurlu 《Journal of Seismology》2018,22(5):1127-1137

We have explored 1D S-wave velocity profiles of shallow and deep soil layers over a basement at strong motion stations in Eskisehir Province, Turkey. Microtremor array explorations were conducted at eight strong motion stations in the area to know shallow 1D S-wave velocity models. Rayleigh wave phase velocity at a frequency range from 3 to 30 Hz was estimated with the spatial autocorrelation analysis of array records of vertical microtremors at each station. Individual phase velocity was inverted to a shallow S-wave velocity profile. Low-velocity layers were identified at the stations in the basin. Site amplification factors from S-wave parts of earthquake records that had been estimated at the strong motion stations by Yamanaka et al. (2017) were inverted to the S-wave velocities and Q-values of the sedimentary layers. The depths to the basement with an S-wave velocity of 2.2 km/s are about 1 km in the central part of the basin, while the basement becomes shallow as 0.3 km in the marginal part of the basin. We finally discussed the effects of the shallow and deep sedimentary layers on the 1D S-wave amplification characteristics using the revealed profiles. It is found that the shallow soil layers have no significant effects in the amplification at a frequency range lower than 3 Hz in the area.  相似文献   

Spatial distribution, diversity and composition of bacterial communities in sub-seafloor fluids at a deep-sea hydrothermal field of the Suiyo Seamount     

Shingo Kato  Kurt Hara  Hiroko Kasai  Takashi Teramura  Michinari Sunamura  Jun-ichiro Ishibashi  Takeshi Kakegawa  Toshiro Yamanaka  Hiroyuki Kimura  Katsumi Marumo  Tetsuro Urabe  Akihiko Yamagishi   《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(10):1844-1855

Spatial distribution, diversity, and composition of bacterial communities within the shallow sub-seafloor at the deep-sea hydrothermal field of the Suiyo Seamount, Izu-Bonin Arc, Western Pacific Ocean, were investigated. Fluids were sampled from four boreholes in this area. Each borehole was located near or away from active vents, the distance ranging 2–40 m from active vents. In addition, fluids discharging from a natural vent and ambient seawater were sampled in this area. We extracted DNA from each sample, amplified bacterial 16S rRNA genes by PCR, cloned the PCR products and sequenced. The total number of clones analyzed was 348. Most of the detected phylotypes were affiliated with the phylum Proteobacteria, of which the detection frequency in each clone library ranged from 84.6% to 100%. The bacterial community diversity and composition were different between hydrothermal fluids and seawater, between fluids from the boreholes and the vent, and even among fluids from each borehole. The relative abundances of the phylotypes related to Thiomicrospira, Methylobacterium and Sphingomonas were significantly different among fluids from each borehole. The phylotypes related to Thiomicrospira and Alcanivorax were detected in all of the boreholes and vent samples. Our findings provide insights into bacterial communities in the shallow sub-seafloor environments at active deep-sea hydrothermal vent fields.  相似文献   

Mineralogy and geochemistry of shallow sediments of Sonargaon, Bangladesh and implications for arsenic dynamics: Focusing on the role of organic matter     

Ashraf Ali Seddique  Harue MasudaMuneki Mitamura  Keiji ShinodaToshiro Yamanaka  Shinji NakayaKazi Matin Ahmed 《Applied Geochemistry》2011,26(4):587-599

Mineralogy and geochemistry of modern shallow sediments (up to 5 m thick) within the zone of water table fluctuations were studied to determine the likely sources and processes responsible for releasing As into groundwater. Samples were collected from different geological settings with varying groundwater As concentrations during dry (December 2005) and wet (September 2006) seasons at Sonargaon, Bangladesh. Stratigraphic sequences of the studied sediments showed three distinct lithofacies, viz. clayey-silt, silty-clay, and silty-very fine sand, corresponding to fine-grained overbank associations. Total As concentrations of shallow sediments ranged from <1 to 16 mg/kg without a significant difference in the range of As concentrations between the seasons. Sequential chemical extraction analysis of As revealed that >80% of the As was fixed in insoluble and organic phases, while the amount of As in reducible and acid-soluble phases was very low (<20%) and varied inversely with total As content. Total As concentration varied with mica content (muscovite and biotite) and its related elements (Al, Mg and Fe), but not with total organic C, suggesting that biotite is the major host phase of As. Arsenic appears to be liberated from biotite and/or other As-bearing minerals via chemical weathering (i.e., hydration-decomposition), either from the near-surface sediments which are subject to seasonal cycling of the redox conditions, or from within the aquifer sediments. Once released, progressive diagenesis to form As-bearing organic matter may be responsible for controlling As distribution in the sediments and coexisting groundwater of the study area.  相似文献   

Strong ground motion simulation during the November 1759 Earthquake along Serghaya Fault in the metropolitan of Damascus, Syria     

Hussam Eldein Zaineh  Hiroaki Yamanaka  Yadab Prasad Dhakal  Rawaa Dakkak  Mohamad Daoud 《Journal of Seismology》2013,17(4):1295-1319

The seismic hazard potential for metropolitan of Damascus, Syria is mainly controlled by earthquakes along Serghaya Fault which is a branch of Dead Sea Fault System. In this study, strong ground motion due to the November 1759 Earthquake along the fault of Serghaya was estimated with a numerical simulation technique. In the simulation, the Kostrov-like slip-velocity function was used as an input to the discrete wave number method to simulate the strong ground motions in a broadband frequency range. In order to model the incoherent rupture propagation which can excite large high-frequency waves, random numbers are added to arrival time of circular rupture front. MMI intensities calculated from the synthetic ground motions are compared with the observed values by Ambraseys and Barazangi (J Geophys Res 94:4007-4013, 1989). The calculated intensities are in good agreement with the observed ones at the most sites that validate appropriateness of the proposed source model. The PGA and PGV in the eastern region of Damascus city are higher than those in the western region due to the effects of local site amplification. The simulated high-frequency (1.0–6.0 Hz) ground motions for the sites in the Damascus city are higher than the design requirements defined by the Syrian building code. Furthermore, the simulated high-frequency ground motions for sites in the focal region are bigger than the design requirements in the case of the near-fault factors and are not considered. That demonstrates the appropriateness of considering the near-fault factors for a site near the focal region as introduced by the new building code.  相似文献