Millennium‐scale recurrent uplift inferred from beach deposits bordering the eastern Nankai Trough,Omaezaki area,central Japan     

Osamu Fujiwara  Kazuomi Hirakawa  Toshiaki Irizuki  Shiro Hasegawa  Yoshitaka Hase  Jun‐ichi Uchida  Kohei Abe 《Island Arc》2010,19(3):374-388

A flight of Holocene marine terraces on the southwestern coast of Cape Omaezaki of central Japan provides evidence of recurrent millennium‐scale uplift events. We reconstructed the uplift history of these terraces by using facies analysis of drill core and geoslicer samples, environmental analysis of trace fossils, and ¹⁴C age determinations. Coastal uplift can be identified by the displacement of beach deposits such as foreshore deposits, which represent the intertidal swash zone of a wave‐dominated sandy coast. Three levels of former beach deposits facing the Nankai Trough were identified near the coast in the Omaezaki area. The highest of these, dated at about 3020–2880 BC, records a maximum of 2.2–2.7 m of emergence. The middle beach surface, of minimum age 370–190 BC, shows 1.6–2.8 m of emergence. The lowest beach surface, which is older than 1300–1370 AD, records 0.4–1.6 m of emergence. Our analysis of vertical crustal deformation data during the Holocene in this region suggests that rapid and strong uplift was restricted to the southwestern coast of the Omaezaki area and was probably caused by high‐angle thrusting on subsidiary faults branching from the underlying plate boundary megathrust.  相似文献   

Crustal structure beneath Aso Caldera,Southwest Japan,as derived from receiver function analysis     

Yuki Abe  Takahiro Ohkura  Takuo Shibutani  Kazuro Hirahara  Mamoru Kato 《Journal of Volcanology and Geothermal Research》2010

Aso Volcano experienced a huge pyroclastic eruption 90 thousand years ago, and formed a large caldera (18 km × 25 km). In order to test the hypothesis of a magma body in the mid and lower crust that has been suggested geophysically and geochemically, we investigated seismic velocity discontinuities and velocity structure beneath Aso Caldera using receiver functions and a genetic algorithm inversion. We confirm the existence of the Moho at depths between 30 km and 35 km and a large velocity anomaly should exist in the deep portion of the crust beneath Aso Caldera, from imaging of receiver functions observed only at stations outside the caldera. As a result of a more detailed examination with GA inversion, a low velocity layer is detected at depths between 10 km and 24 km beneath the western part of the caldera. S-wave velocity of the layer is estimated to be 2.0–2.4 km/s. We estimate that the low velocity layer contains at most 15% melt or 30% aqueous fluid. The layer exists near the Conrad and at the same depths as the swarm of the low frequency earthquakes and a compressional and dilatational deformation source which are expected to be caused by fluid movement beneath the middle-eastern part of the caldera. Fluid contained in the layer might be related with huge pyroclastic eruptions of Aso Volcano.  相似文献   

Estimation of the 2D crustal velocity structure in the Hidaka and Iburi Subprefectures, Hokkaido, Japan     

Ismail Husain Fathi  Kaoru Miyashita 《Arabian Journal of Geosciences》2009,2(3):235-239

Applying the iterative shooting/bisection technique for rapid forward modeling to the seismic explosion data, we could refine the crustal velocity structure model of the western part of the Hidaka collision zone, Hokkaido, Japan. We used only the precise P-wave first arrival data obtained by the Research Group for Explosion Seismology, which set up a 113.4-km-long profile in August 2000 along with 327 observation points and four shot points with TNT charges from 100 to 300 kg. We could estimate a two-dimensional inhomogeneous crustal velocity structure model with a velocity decrease in the eastern direction at a depth of 15.7 km, several portions of velocity reversals with depth and a low velocity anomaly proposed in previous studies. The root-mean-square of travel-time residuals was improved from 0.398 s for the previous structure model to 0.176 s for the present model with a reduction of 55.8%.  相似文献   

Modeling African equatorial ionosphere using ordinary Kriging interpolation technique for GNSS applications     

O. E. Abe  A. B. Rabiu  O. S. Bolaji  E. O. Oyeyemi 《Astrophysics and Space Science》2018,363(8):168

The ability to model the ionosphere accurately for single frequency users in satellite applications has gained some appreciable usage, most especially during quiet conditions in a mild (middle latitudes) ionosphere. However, solving the problem of ionosphere for single frequency user of Global Navigation Satellite Systems (GNSS) in equatorial ionization anomaly (EIA) region is of a great concern for space scientists and engineers. Several methodologies have been used to develop models that describe global or regional maps for ionosphere errors in order to mitigate the effect of the errors on GNSS systems. Global or regional ionosphere Maps have been known to be an efficient tool to monitor the delay introduced by the ionosphere in the satellite signals. This research uses the conventional Planar fit and ordinary Kriging methodologies to assess a regional map for ionosphere correction in equatorial African sector. The result obtained is an indication that modified Kriging methodology describes the EIA ionosphere corrections better compared with ordinary Kriging and Planar fit methodologies.  相似文献   

The effect of a tidal cycle on the dynamics of nutrients in a tidal estuary in the Seto Inland Sea, Japan   总被引：4，自引：0，他引：4  

Shigeru Montani  Paolo Magni  Megumi Shimamoto  Nao Abe  Koichi Okutani 《Journal of Oceanography》1998,54(1):65-76

A 24 hour time series survey was carried out during a spring tide (tidal range ca.2 m) of May 1995 on a tidal estuary in the Seto Inland Sea, Japan, in the context of an integrated program planned to quantify the dynamics of biophilic elements (carbon, nitrogen and phosphorus) and the roles played by the macrobenthos on the processes. Three stations were set along a transect line of about 1.4 km, which linked the river to the rear to the innermost part of the subtidal zone. Every hour, at each station, measurements were made of surface water temperature, salinity and dissolved oxygen concentration, and surface water was collected for the determination of nutrients [NH₄ ⁺−N, (NO₃ ⁻+NO₂ ⁻)−N, PO₄ ³⁻−P and Si (OH)₄−Si]. During the ebb flow, riverine input of silicate and nitrate+nitrite significantly increased the concentrations of both the intertidal and the subtidal stations. Conversely, during the high tide, river nutrient concentrations were lowered by the mixing of fresh water with sea water. As a result, best (inverse) correlations were found at the river station for salinity against silicate (y=-2.9 Sal.+110.7,r ²=0.879) and nitrate+nitrite (y=-1.3 Sal.+48.4,r ²=0.796). In contrast, ammonium nitrogen concentrations were higher at intermediate salinities. Indeed, no significant correlation was found between salinity and ammonium. The effect of the macrobenthos, which is abundant on the intertidal flat, is discussed as a biological component that influences the processes of nutrient regeneration within the estuary. The effect of the tidal amplitude is an important one in determining the extent of the variations in nutrient concentrations at all three stations, which were stronger between the lower low tide and the higher high tide.  相似文献   

Estimating of gas transfer velocity using triple isotopes of dissolved oxygen     

V. V. S. S. Sarma  Osamu Abe  Makio Honda  Toshiro Saino 《Journal of Oceanography》2010,66(4):505-512

The atmosphere-ocean exchange of climatically important gases is determined by the transfer velocity (k) and concentration gradient across the interface. Based on observations in the northwestern subarctic Pacific and Sagami Bay, we report here the results of the first ever application of the natural abundance of triple isotopes of dissolved oxygen (¹⁶O, ¹⁷O and ¹⁸O) for direct estimation of k and propose a new relationship with wind speed. The k values estimated from nighttime variations in oxygen isotopes are found to be higher than the direct estimations at low wind speed (<5 m s⁻¹) and lower at high wind speeds (>13 m s⁻¹) and showed significant spatial variability. The method presented here can be used to derive seasonal and spatial variations in k and the influence of surface conditions on the value, leading to improved estimates of biogenic/anthropogenic gas exchange at the air-sea interface.  相似文献   

Improving the prospects for detecting extrasolar planets in gravitational microlensing events in 2002     

I. A.Bond  F.Abe  R. J.Dodd  J. B.Hearnshaw  P. M.Kilmartin  K.Masuda  Y.Matsubara  Y.Muraki  S.Noda  O. K. L.Petterson  N. J.Rattenbury  M.Reid  To.Saito  Y.Saito  T.Sako  J.Skuljan  D. J.Sullivan  T.Sumi  S.Wilkinson  R.Yamada  T.Yanagisawa  P. C. M.Yock 《Monthly notices of the Royal Astronomical Society》2002,331(2):L19-L23

Gravitational microlensing events of high magnification have been shown to be promising targets for detecting extrasolar planets. However, only a few events of high magnification have been found using conventional survey techniques. Here we demonstrate that high-magnification events can be readily found in microlensing surveys using a strategy that combines high-frequency sampling of target fields with on-line difference imaging analysis. We present 10 microlensing events with peak magnifications greater than 40 that were detected in real-time towards the Galactic bulge during 2001 by the Microlensing Observations in Astrophysics (MOA) project. We show that Earth-mass planets can be detected in future events such as these through intensive follow-up observations around the event peaks. We report this result with urgency as a similar number of such events are expected in 2002.  相似文献   

A search for collision orbits in the free-fall three-body problem I. Numerical procedure     

Kiyotaka Tanikawa  Hiroaki Umehara  Hiroshi Abe 《Celestial Mechanics and Dynamical Astronomy》1995,62(4):335-362

A numerical procedure is devised to find binary collision orbits in the free-fall three-body problem. Applying this procedure, families of binary collision orbits are found and a sequence of triple collision orbits are positioned. A property of sets of binary collision orbits which is convenient to search triple collision orbits is found. Important numerical results are formulated and summarized in the final section.  相似文献   

Effect of nutrient release from sea floor on Si:P ratio in the Buzen-Kai,western Seto Inland Sea,in summer     

Kazuo Abe  Mutsumi Tsujino  Norihisa Nakagawa  Katsuyuki Abo 《Journal of Oceanography》2015,71(2):221-227

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Apodized Lyot coronagraph for SPHERE/VLT: II. Laboratory tests and performance     

G��raldine Guerri  Jean-Baptiste Daban  Sylvie Robbe-Dubois  Richard Douet  Lyu Abe  Jacques Baudrand  Marcel Carbillet  Anthony Boccaletti  Philippe Bendjoya  Carole Gouvret  Farrokh Vakili 《Experimental Astronomy》2011,30(1):59-81

SPHERE (which stands for Spectro-Polarimetric High-contrast Exoplanet REsearch) is a second-generation Very Large Telescope (VLT) instrument dedicated to high-contrast direct imaging of exoplanets whose first-light is scheduled for 2011. Within this complex instrument one of the central components is the apodized Lyot coronagraph (ALC). The principal aim of this paper is to report the first laboratory experiment of the ALC designed for the SPHERE instrument. The performance and sensitivity of the optical configuration was first numerically studied with an end-to-end approach (see the results in paper I subtitled ??Detailed numerical study??). Made confident by the results, we then tested a prototype on an infrared coronagraphic bench. We measured the transmission profiles of the apodizer prototype and the coronagraphic performance of the apodized Lyot coronagraph in Y, J, and H bands. The coronagraph sensitivity to lateral and longitudinal misalignments of its three main components (apodizer, coronagraphic mask and Lyot stop) was finally studied in H band. We can conclude that the prototype meets the SPHERE technical requirements for coronagraphy.  相似文献