Piezomagnetic potentials due to an inclined rectangular fault in a semi-infinite medium   总被引：2，自引：0，他引：2  

Mitsuru Utsugi  Yasunori Nishida  & Yoichi Sasai 《Geophysical Journal International》2000,140(3):479-492

Analytical solutions for the piezomagnetic potentials are derived for strike-slip, dip-slip and tensile-opening fault motions with arbitrary dip and strike angles, so as to be applicable in various types of earthquakes. These solutions are expressed as the composition of elementary functions which are identical to the magnetic potentials produced by magnetic dipoles, quadrupoles and octupoles distributed on the fault plane and other planes. Therefore, the geomagnetic field changes due to the piezomagnetic effect are expressed by the superposition of the fields produced by these equivalent sources.
Examples of calculated results show characteristic features for various types of fault motions as follows: (1) the pattern of the geomagnetic field changes becomes significantly different depending on the strike direction, although the maximum amplitude is almost the same for all directions; (2) the geomagnetic field change reaches a maximum at a dip angle of 90° for strike-slip and tensile-opening fault motions and at 45° for dip-slip fault motion.  相似文献   

Geoarchaeological studies in Nara,Japan: The integrated findings     

Gina L. Barnes  Shiro Nishida  Masaaki Okita 《Geoarchaeology》2005,20(8):837-860

In this article, the authors summarize 20 years of scholarship and two field projects on geoarchaeology in Nara, Japan, carried out by researchers from 12 different institutions in 4 countries. The research goal was to test an aerial photographic reconstruction of surface landforms in the Nara Basin with subsurface data. Project A was conducted at Asawa; it tested, through geological coring, whether a suspected swampy backmarsh in the eastern basin existed and whether it would yield data on the transition to wet rice agriculture in the mid‐1st millennium B.C. Project B was conducted at Miwa; it tested, through geological coring and subsequent excavation, the nature of upland agricultural terrace formation in the southeastern basin and whether the suspected existence of a 4th‐century palace site could be confirmed. Two layers of carbonaceous clay at Asawa were dated to the Early (˜5000–3500 B.C.) and Final (˜1000‐300 B.C.) phases of the Jomon period. Pollen data revealed the establishment of an evergreen oak forest from 5,000 years ago and anthropogenic changes in forest cover from 2,000 years ago. Phytoliths from rice, millets, reeds, and bamboo were recovered in layers postdating the Final Jomon carbonaceous clay. A fault scarp with anthropogenic modification of the terraces was identified at Miwa. It was discovered that an incised stream valley had been infilled in the Medieval period at the same time surface layers were razed; the front of the terrace was extended in the premodern period. Remains were recovered from the Middle Yayoi (˜100 B.C.–A.D. 100) and the Medieval (˜A.D. 1185–1603) periods. However, as the terracing involved razing the early historic levels, no data were recovered on the alleged 4th‐century palace site. The significance of these findings lies in the identification of (a) a swampy backmarsh at Asawa, where initial agricultural efforts in growing wet rice in the basin may have occurred, confirming the aerial photographic reconstruction; and (b) hillside terracing activities at Miwa, from the Medieval period onwards, which have radically changed the configuration of the natural topography. © 2005 Wiley Periodicals, Inc.  相似文献   

The variability of Magellanic cluster infrared stars     

S. Nishida  T. Tanabé  Y. Nakada  S. Matsumoto  K. Sekiguchi  I. S. Glass 《Monthly notices of the Royal Astronomical Society》2000,313(1):136-140

We report on the light variations of the infrared stars that were discovered recently in the Magellanic clusters NGC 419, 1783 and 1978. Their periods, of 528, 458 and 491 days, are among the longest known for carbon-rich Mira variables in the Clouds. All three IR stars were found to lie on the extension of the period– M _bol relation derived from the shorter-period C-rich Miras while they were 0.45–0.70 mag fainter than the extension of the period– M _K relation. Their main sequence masses were determined by isochrone fitting to be 1.5–1.6 M_⊙, consistent with the prediction of the evolutionary models of Vassiliadis & Wood.  相似文献   

The Impact of the Winter Monsoon on Marine Surface-Layer Turbulence     

Tomoya Nishida  Takuji Waseda 《Boundary-Layer Meteorology》2015,157(1):141-156

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A new approach for mobile and expandable real-time deep seafloorobservation - adaptable observation system     

Kawaguchi  K. Hirata  K. Nishida  T. Obana  S. Mikada  H. 《Oceanic Engineering, IEEE Journal of》2002,27(2):182-192

Although submarine cable in-line seafloor observation systems are very effective tools for real-time/long-term geo-scientific measurements,, there are technological difficulties for deploying as many sensors as on land. To solve this problem, JAM-STEC developed an expandable and replaceable satellite measurement station called the adaptable observation system (AOS). The AOS is a battery operated mobile observatory connected to the backbone cable system by a 10 km long thin fiber cable to ensure real-time data recovery. The system consists of a branching system, a junction box, a fiber cable, and a battery system for a six-month operation. Installation and construction of the AOS will be conducted by a towed vehicle and an ROV. A thin fiber cable-laying system was developed and tested for practical operation. This observation system provides a chance to extend existing seafloor networks from an in-line area to a wider area  相似文献   

Distinctive erosional and depositional structures formed at a canyon mouth: A lower Pleistocene deep‐water succession in the Kazusa forearc basin on the Boso Peninsula,Japan     

Makoto Ito  Kazuaki Ishikawa  Naohisa Nishida 《Sedimentology》2014,61(7):2042-2062

The canyon mouth is an important component of submarine‐fan systems and is thought to play a significant role in the transformation of turbidity currents. However, the depositional and erosional structures that characterize canyon mouths have received less attention than other components of submarine‐fan systems. This study investigates the facies organization and geometry of turbidites that are interpreted to have developed at a canyon mouth in the early Pleistocene Kazusa forearc basin on the Boso Peninsula, Japan. The canyon‐mouth deposits have the following distinctive features: (i) The turbidite succession is thinner than both the canyon‐fill and submarine‐fan successions and is represented by amalgamation of sandstones and pebbly sandstones as a result of bypassing of turbidity currents. (ii) Sandstone beds and bedsets show an overall lenticular geometry and are commonly overlain by mud drapes, which are massive and contain fewer bioturbation structures than do the hemipelagic muddy deposits. (iii) The mud drapes have a microstructure characterized by aggregates of clay particles, which show features similar to those of fluid‐mud deposits, and are interpreted to represent deposition from fluid mud developed from turbidity current clouds. (iv) Large‐scale erosional surfaces are infilled with thick‐bedded to very thick‐bedded turbidites, which show lithofacies quite similar to those of the surrounding deposits, and are considered to be equivalent to scours. (v) Concave‐up erosional surfaces, some of which face in the upslope direction, are overlain by backset bedding, which is associated with many mud clasts. (vi) Tractional structures, some of which are equivalent to coarse‐grained sediment waves, were also developed, and were overlain locally by mud drapes, in association with mud drape‐filled scours, cut and fill structures and backset bedding. The combination of these outcrop‐scale erosional and depositional structures, together with the microstructure of the mud drapes, can be used to identify canyon‐mouth deposits in ancient deep‐water successions.  相似文献   

Sound velocity measurements in dhcp-FeH up to 70 GPa with inelastic X-ray scattering: Implications for the composition of the Earth's core     

Yuki Shibazaki  Eiji Ohtani  Hiroshi Fukui  Takeshi Sakai  Seiji Kamada  Daisuke Ishikawa  Satoshi Tsutsui  Alfred Q.R. Baron  Naoya Nishitani  Naohisa Hirao  Kenichi Takemura 《Earth and Planetary Science Letters》2012

We have determined the density evolution of the sound velocity of dhcp-FeH_x (x ≈ 1) up to 70 GPa at room temperature, by inelastic X-ray scattering and by X-ray diffraction. We find that the variation of V_P with density is different for the ferromagnetic and nonmagnetic dhcp-FeH_x, and that only nonmagnetic dhcp-FeH_x follows Birch's law. Combining our results with Birch's law for iron and assuming an ideal two-component mixing model, we obtain an upper bound of the hydrogen content in the Earth's inner core, 0.23(6) wt.% H, corresponding to FeH_0.13(3). The iron alloy with 0.23(6) wt.% H can satisfy the density, and compressional and shear sound velocities of the PREM inner core, assuming that there are no other light elements in the inner core.  相似文献   

Sound velocity measurement in liquid water up to 25 GPa and 900 K: Implications for densities of water at lower mantle conditions     

Yuki Asahara  Motohiko Murakami  Yasuo Ohishi  Naohisa Hirao  Kei Hirose 《Earth and Planetary Science Letters》2010,289(3-4):479-485

We extended the pressure range of sound velocity measurements for liquid water to 25 GPa and 900 K along the melting curve using a laser heated diamond anvil cell with a combined system of Brillouin scattering and synchrotron X-ray diffraction. Experimental pressure and temperature were obtained by solving simultaneous equations: the melting curve of ice and the equation of state for gold. The sound velocities obtained in liquid water at high pressures and melting temperatures were converted to density using Murnaghan's equation of state by fitting a parameter of the pressure derivative of bulk modulus at 1 GPa. The results are in good agreement with the values predicted by a previously reported equation of state for water based on sound velocity measurements. The equation of state for water obtained in this study could be applicable to water released by dehydration reactions of dense hydrous magnesium silicate phases in cold subducting slabs at lower mantle conditions, although the validity of Murnaghan's equation of state for water should be evaluated in a wider pressure and temperature ranges. The present velocity data provides the basis for future improvement of the accurate thermodynamic model for water at high pressures.  相似文献   

Constraining sediment provenance for tsunami deposits using distributions of grain size and foraminifera from the Kujukuri coastline and shelf,Japan     

Jessica E. Pilarczyk  Yuki Sawai  Dan Matsumoto  Yuichi Namegaya  Naohisa Nishida  Ken Ikehara  Osamu Fujiwara  Chris Gouramanis  Tina Dura  Benjamin P. Horton 《Sedimentology》2020,67(3):1373-1392

Tsunami deposits preserved in the geological record provide a more comprehensive understanding of their patterns of frequency and intensity over longer timescales; but recognizing tsunami deposits can prove challenging due to post-depositional changes, lack of contrast between the deposits and surrounding sedimentary layers, and differentiating between tsunami and storm deposition. Modern baseline studies address these challenges by providing insight into modern spatial distributions that can be compared with palaeotsunami deposits. This study documents the spatial fingerprint of grain size and foraminifera from Hasunuma Beach and the Kujukuri shelf to provide a basis from which tsunami deposits can be interpreted. At Hasunuma Beach, approximately 50 km east of Tokyo, the spatial distribution of three common proxies (foraminiferal taxonomy, foraminiferal taphonomy and sediment grain size) for tsunami identification were mapped and clustered using Partitioning Around Medoids cluster analysis. Partitioning Around Medoids cluster analysis objectively discriminated two coastal zones corresponding to onshore and offshore sample locations. Results show that onshore samples are characterized by coarser grain sizes (medium to coarse sand) and higher abundances of Pararotalia nipponica (27 to 63%) than offshore samples, which are characterized by finer grain sizes (fine to medium sand), lower abundances of Pararotalia nipponica (2 to 19%) and Ammonia parkinsoniana (0 to 10%), higher abundances of planktonics (15 to 58%) and species with fragile tests including Uvigerinella glabra. When compared to grain-size and foraminiferal taxonomy, foraminiferal taphonomy; i.e. surface condition of foraminifera, a proxy not commonly used to identify tsunami deposits, was most effective in discriminating modern coastal zones (identified supratidal, intertidal and offshore environments) and determining sediment provenance for tsunami deposits at Kujukuri. This modern baseline study assists the interpretation of tsunami deposits in the geological record because it provides a basis for sediment provenance to be determined.  相似文献   

In Search of the Cretaceous-Tertiary Boundary in Heilongjiang River Area of China   总被引：1，自引：0，他引：1  

Sun G  M.Akhmetiev  Dong Z.M  A.R.Ashraf  Sun Y.W  E.Bugdaeva  D.L.Dilcher  L.Golovneva  I.Harding  K.Johnson  T.Kezina  T.Kodrul  LU J.S  V.Markevich  H.Nishida  H.Okada  Park S.O  Sun C.L  Xiong X.Z  Xing Y.L  Zhou Z.L 《世界地质(英文版)》2002,5(2)

Abstract A new geological section recognized in Baishantou of Jiayin, Heilongjiang Province, China, was studied preliminarily in searching for the K/T boundary. An early Paleocene florule characrerized by abundant Tiliaephyllum tsagajanicum leaves and its associated plants, was collected from the Baishantou Member (new member representing the lower part of the Paleocene Wuyun Formation) overlying the possible K/T boundary. A tuff bed was found from the upper part of the Furao Formation (uppermost Cretaceous) in this section. The new findings imply that the K/T boundary is probable lying in the interval between the base of the Baishantou Member and the tuff bed, based on the correlation of the present strata with the stratotype of the Tsagajan Group spanning the K/T boundary in "Belaya Gara" of the Bureya Basin, Russia. The early Paleocene florule from the Baishantou Member and the early-middle Maastrichtian dinosaurs found from the Yuliangzi Formation underlying the Furao Formation suggest that the Baishantou section is more promising for searching for the K/T boundary in this area. Further studies of the section is needed, integrating paleontological, biostratigraphic, geochemical, paleomagnetic, and sedimentary research would benefit our understanding the mass extinction event and biotic recovery in the Heilongjiang River area, China, and even all of northeast Asia during the K/T boundary interval.  相似文献