Evidence for erosion and deposition by the 2011 Tohoku-oki tsunami on the nearshore shelf of Sendai Bay,Japan     

Shuro?YoshikawaEmail author  Toshiya?Kanamatsu  Kazuhisa?Goto  Izumi?Sakamoto  Masatoshi?Yagi  Mikio?Fujimaki  Riichirou?Imura  Kenji?Nemoto  Hide?Sakaguchi 《Geo-Marine Letters》2015,35(4):315-328

Ongoing geological research into processes operating on the nearshore continental shelf and beyond is vital to our understanding of modern tsunami-generated sediment transport and deposition. This paper investigates the southern part of Sendai Bay, Japan, by means of high-resolution seismic surveys, vibracoring, bathymetric data assimilation, and radioisotope analysis of a core. For the first time, it was possible to identify an erosional surface in the shallow subsurface, formed by both seafloor erosion and associated offshore-directed sediment transport caused by the 2011 Tohoku-oki tsunami. The area of erosion and deposition extends at least 1,100 m offshore from the shoreline down to water depths of 16.7 m. The tsunami-generated sedimentological signature reaches up to 1.2 m below the present seafloor, whereas bathymetric changes due to storm-related reworking over a period of 3 years following the tsunami event have been limited to the upper ~0.3 m, despite the fact that the study area is located on an open shelf facing the Pacific Ocean. Tsunami-generated erosion surfaces may thus be preserved for extended periods of time, and may even enter the rock record, because the depth of tsunami erosion can exceed the depth of storm erosion. This finding is also important for interpretation of modern submarine strata, since erosion surfaces in shallow (depths less than ~1 m) seismic records from open coast shelves have generally been interpreted as storm-generated surfaces or transgressive ravinement surfaces.  相似文献   

Estrogenic activity in sediments contaminated by nonylphenol in Tokyo Bay (Japan) evaluated by vitellogenin induction in male mummichogs (Fundulus heteroclitus)     

Kurihara R  Watanabe E  Ueda Y  Kakuno A  Fujii K  Shiraishi F  Hashimoto S 《Marine pollution bulletin》2007,54(9):1315-1320

Estrogenic activity was determined in sediments collected from Tokyo Bay. Sampling was performed at five stations including the site near the sewage treatment plant. The most estrogenic sediment collected near the sewage treatment plant was fractionated into ten fractions using normal-phase high-performance liquid chromatography. Chemical analysis was carried out for each fraction and nonylphenol (NP, 20,700 ng g⁻¹ dry wt) was detected at a higher concentration than estron (2.39 ng g⁻¹ dry wt) and 17β-estradiol (<0.7 ng g⁻¹ dry wt). Furthermore, each fraction was administered to male mummichogs (Fundulus heteroclitus), and vitellogenin (Vtg) was measured after two weeks. The induction of Vtg was observed; this estrogenic potency could be attributed to the NP content in this fraction. This is the first report to suggest that the high NP concentration in the sediments from Tokyo Bay has the potential to induce Vtg in wild fish.  相似文献   

QSAT: The Satellite for Polar Plasma Observation     

Yoshihiro Tsuruda  Akiko Fujimoto  Naomi Kurahara  Toshiya Hanada  Kiyohumi Yumoto  Mengu Cho 《Earth, Moon, and Planets》2009,104(1-4):349-360

This paper introduces QSAT, the satellite for polar plasma observation. The QSAT project began in 2006 as an initiative by graduate students of Kyushu University, and has the potential to contribute greatly to IHY (International Heliophysical Year) by showing to the world the beauty, importance, and relevance of space science. The primary objectives of the QSAT mission are (1) to investigate plasma physics in the Earth’s aurora zone in order to better understand spacecraft charging, and (2) to conduct a comparison of the field-aligned current observed in orbit with ground-based observations. The QSAT project can provide education and research opportunities for students in an activity combining space sciences and satellite engineering. The QSAT satellite is designed to be launched in a piggyback fashion with the Japanese launch vehicle H-IIA. The spacecraft bus is being developed at the Department of Aeronautics and Astronautics of Kyushu University with collaboration of Fukuoka Institute of Technology. Regarding the payload instruments, the Space Environment Research Center of Kyushu University is developing the magnetometers, whereas the Laboratory of Spacecraft Environment Interaction Engineering of Kyushu Institute of Technology is developing the plasma probes. We aim to be ready for launch in 2009 or later.  相似文献   

A heating process of Kuchi-erabu-jima volcano,Japan, as inferred from geomagnetic field variations and electrical structure     

Wataru Kanda  Mitsuru Utsugi  Yoshikazu Tanaka  Takeshi Hashimoto  Ikuko Fujii  Toshiaki Hasenaka  Nobuaki Shigeno 《Journal of Volcanology and Geothermal Research》2010,189(1-2):158-171

Since August 2000, we have recorded the total intensity of the geomagnetic field at the summit area of Kuchi-erabu-jima volcano, where phreatic eruptions have repeatedly occurred. A time series analysis has shown that the variations in the geomagnetic field since 2001 have a strong relationship to an increase in volcanic activity. These variations indicate thermal demagnetization of the subsurface around the presently active crater. The demagnetization source for the early variations, until summer 2002, was estimated at about 200 m below sea level. For the variations since 2003, the source was modeled on the basis of the expansion of a uniformly magnetized ellipsoid. The modeling result showed that the source is located at 300 m above sea level beneath the crater. We carried out an audio-frequency magnetotelluric survey with the aim of obtaining a relation between the demagnetization source and the shallow structure of the volcano. A two-dimensional inversion applied to the data detected two good conductors, a shallow thin one which is restricted to a region around the summit area, while the other extends over the edifice at depths between 200 and 800 m. These conductors are regarded as clay-rich layers with low permeability, which were assumed to be generated through hydrothermal alteration. The demagnetization source for the early variations was possibly located at the lower part of the deep conductor and the source after 2003 lies between the two conductors, where groundwater is considered to be abundant. Based on these results, as well as on seismological, geodetic, and geochemical information, we propose a heating process of the Kuchi-erabu-jima volcano. In the initial stage, high-temperature volcanic gases supplied from the deep-seated magma remained temporarily at the level around the lower part of the less permeable deep conductor since the ascent path had not yet been established. Then, when the pathway developed as a result of repeated earthquakes, it became possible for a massive flux of volcanic gases to ascend through the conductor. The high temperature gases reached the aquifer located above the conductor and the heat was efficiently transported to the surrounding rocks through the groundwater. As a consequence, an abrupt increase of the gas flux and diffusion of the heat through the aquifer occurred and the high-temperature zone expanded. Since the high-temperature zone is located beneath another conductor, which acts as caprock, we assume that the energy of the phreatic explosion is accumulated there.  相似文献   

Gray box identification of flexible structures: application to robust active vibration suppression control     

A. Forrai  S. Hashimoto  A. Isojima  H. Funato  K. Kamiyama 《地震工程与结构动力学》2001,30(8):1203-1220

The paper deals with gray box identification of flexible structures and active vibration suppression from a robust control perspective. First, the linearized mathematical model of an N‐storey flexible structure is presented. Next, the generalized mathematical model is particularized for the investigated three‐storey flexible structure. The considered flexible structure is identified based on black box and gray box identification methods and the model's parametric uncertainties are deduced. Furthermore, control constraints are presented for the design problem, in case of velocity as well as acceleration feedback, from a robust control perspective. Finally, the effectiveness of the control system is tested through experiments, when the input disturbance is assumed to be a sinusoidal one as well as a historical earthquake record (1940 El Centro record). Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Electrokinetic phenomena associated with a water injection experiment at the Nojima fault on Awaji Island, Japan   总被引：2，自引：0，他引：2  

Hideki Murakami  Takeshi Hashimoto  Naoto Oshiman  Satoru Yamaguchi  Yoshimori Honkura  Norihiko Sumitomo 《Island Arc》2001,10(3-4):244-251

Abstract Self-potential variations were measured to estimate the magnitude of electrokinetic and hydrological parameters (zeta potential and permeability) of the Nojima Fault zone in Awaji, Japan. The study observed self-potential variations that seemed to be associated with water flow from the injection well to the fracture zone, which were induced by turning the injection on and off. Amplitudes of the variations were a few to 0.03 V across 320–450 m dipoles. These variations can be explained well with an electrokinetic model. The quantity k/ζ (permeability/zeta potential) is in the range 1.6 × 10⁻¹³− 5.4 × 10⁻¹³ m²/V. Permeability of the Nojima fault zone can be estimated as approximately 10⁻¹⁶–10⁻¹⁵ m² on the assumption that the zeta potential is in the range –0.01 to –0.001 V.  相似文献   

Detection of crustal inhomogeneity in the Nojima Fault zone using earth current noise     

Takeshi Hashimoto 《Island Arc》2001,10(3-4):306-317

Abstract A resistivity survey method using artificial telluric noise was examined and applied to a field of a fault zone. The electric earth current was measured at 50 sites in the Nojima Fault zone, which is in the northwestern part of Awaji Island, southwestern Japan. The dominant component of the observed electric field is supposed to be leakage currents from DC electric railways running outside the island. Amplitude and polarization of the stray current were systematically investigated and were revealed to represent the subsurface electrical structure of the study area. Some features on the fault zone's electrical structure have been pointed out, including: (i) an electrical boundary that corresponds to a geological one between granite (resistive) and sediments (conductive); and (ii) a low resistivity spot on the surface rupture of the earthquake fault. The structure estimated in the present study is both qualitatively and quantitatively consistent with previous resistivity surveys done using other methods pursued in the same area. It shows the validity of the 'stray current method' as one that is easy and uses low-cost resistivity exploration tools in a region where the effect of artificial noise caused mainly by leakage currents from electrical railways cannot be ignored.  相似文献   

Geochemistry of apatites in the granitic rocks of the Molybdenum, Tungsten, and Barren provinces of Southwest Japan     

A. Tsusue  M. Nedachi  K. Hashimoto 《Journal of Geochemical Exploration》1981,15(1-3)

Recognition of the importance of chlorine complexing in enhancing the solubility of metal sulfides in aqueous solutions has led to the view that the chlorine content of intrusive rock could govern the ability of a magma to separate a metal-rich hydrothermal phase. This article presents the chlorine and fluorine contents of apatites in the granitic rocks of the Barren, Tungsten, and Molybdenum provinces of Southwest Japan.The abundance of Cl in apatites correlates negatively with rock D.I. (differentiation indices), and the abundance of F in apatites correlates positively with rock D.I. The abundance of Cl in apatites of the Molybdenum province is generally higher than that of the Tungsten and Barren provinces, and the abundance of F in apatites in the Molybdenum province is generally lower than that of F in apatites of the Tungsten and Barren provinces.Apatites in the granitic rocks associated with tungsten and fluorite mineralization and granite pegmatite formation, and from the Barren province are mostly F-OH apatites  相似文献   

Numerical modelling of the three-dimensional stress field in southwestern Japan     

Manabu Hashimoto 《Tectonophysics》1982,84(2-4)

It has been inferred from the focal mechanism of earthquakes and their hypocenter distribution (Shiono, 1977) that the stress field in southwestern Japan indicates complicated features; a NW-SE compression at shallow depths along the Nankai trough, an E-W or ESE-WNW compression in the inland crust, an extension parallel to the leading edge of the Philippine Sea plate at subcrustal depths in the region from the southern Chubu to northwestern Shikoku, and a down-dip tension beneath the Kyushu island.In order to investigate possible sources of these complex features of the stress state, a three-dimensional finite element method is employed to model the configuration of the subducting Philippine Sea plate, taking into consideration the following three possible types of forces:

1. (1) A negative buoyancy due to the density contrast between the subducting plate and the surrounding mantle.

2. (2) A northwestward compressive force generated by the movement of the Philippine Sea plate.

3. (3) A westward compressive force due to the movement of the Pacific plate.

For various combinations of different magnitudes of these forces, and of different elastic moduli, the stresses at a number of selected sites are calculated, and their directions are compared with those inferred from the focal mechanism and other geophysical information.It is found that the observed extensional stresses parallel to the leading edge of the subducting Philippine Sea plate may be caused mainly by the negative buoyancy. The northwestward compressive force may not play an important role in generating the complex stress field in southwestern Japan. The observed E-W compressional stress field prevailing in the inland region appears to result mainly from the westward-moving Pacific plate. The present results suggest that if a thin low-velocity transitional layer exists just above the subducting Philippine Sea plate, it could give appreciable effects on the mechanism of low-angled thrust faulting off the Kii peninsula and the Shikoku island.The magnitude of the shear stress in the continental crust and in the subducting plate is estimated to be of the order of several hundred bars, although the calculated shear stresses are considerably affected by the configuration of the subducting plate and also by the applied forces.It is interesting that the stress distribution appears to have some relations to seismicity of subcrustal earthquakes, and to the rupture process of large thrust earthquakes along the plate boundary.  相似文献   

Anisotropy of magnetic susceptibility and paleomagnetic studies in relation to the tectonic evolution of the Miocene–Pleistocene accretionary sequence in the Boso and Miura Peninsulas, central Japan     

Toshiya Kanamatsu  Emilio Herrero-Bervera 《Tectonophysics》2006,418(1-2):131

Anisotropy of magnetic susceptibility (AMS) and paleomagnetic methods have been applied on the middle Miocene–Pleistocene sedimentary sequence in the Boso and Miura Peninsulas of central Japan in order to identify the invisible regional deformation sense as well as the intensity of deformation of sediments. The southern sequences of the two peninsulas were subjected to syn-sedimentary deformation of folding and faulting generated in compressional tectonics. A previous result of the AMS experiment on the sequences shows a development of a strong magnetic lineation. Thus, it is conceivable that the lineation had to be generated during the process of deformation, and in a direction perpendicular to the shortening. However, the orientation of the magnetic lineations is inconsistent among the different tectonic domains in the southern sequence. The paleomagnetic declination in each domain reveals a clockwise rotation in various degrees. Reconstructed directions of the magnetic lineations show a consistent pattern in the east–west direction, suggesting that the sedimentary sequence was subjected to a north-southward compression. In contrast, the compressive direction of the sediment cover on the Pliocene–Pleistocene sequence reveals a northwest direction. Our results suggest that the Philippine Sea Plate had been subducting northward during the middle Miocene–Pliocene, and changed its direction during the Pliocene.  相似文献