Seismic Refraction Crustal Study Along the Sognefjord, South-West Norway, Employing Ocean-Bottom Seismometers     

Takaya Iwasaki  Markvard A. Sellevoll  Toshihiko Kanazawa  Tor Veggeland †  Hideki Shimamura 《Geophysical Journal International》1994,119(3):791-808

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Earthquake distribution in the subduction zone off eastern Hokkaido, Japan, deduced from ocean-bottom seismographic and land observations     

Takaya Iwasaki  Naoshi Hirata  Toshihiko Kanazawa  Taku Urabe  Yoshinobu Motoya  Hideki Shimamura 《Geophysical Journal International》1991,105(3):693-711

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Observations of microseismicity in the southern Kuril Trench area by arrays of ocean bottom seismometers     

Naoshi Hirata  Toshihiko Kanazawa  Kiyoshi Suyehiro  Takaya Iwasaki  Hideki Shimamura 《Geophysical Journal International》1989,98(1):55-68

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Measurement of methane flux over an evergreen coniferous forest canopy using a relaxed eddy accumulation system with tuneable diode laser spectroscopy detection     

Ayaka Sakabe  Ken Hamotani  Yoshiko Kosugi  Masahito Ueyama  Kenshi Takahashi  Akito Kanazawa  Masayuki Itoh 《Theoretical and Applied Climatology》2012,109(1-2):39-49

Very few studies have conducted long-term observations of methane (CH₄) flux over forest canopies. In this study, we continuously measured CH₄ fluxes over an evergreen coniferous (Japanese cypress) forest canopy throughout 1?year, using a micrometeorological relaxed eddy accumulation (REA) system with tuneable diode laser spectroscopy (TDLS) detection. The Japanese cypress forest, which is a common forest type in warm-temperate Asian monsoon regions with a wet summer, switched seasonally between a sink and source of CH₄ probably because of competition by methanogens and methanotrophs, which are both influenced by soil conditions (e.g., soil temperature and soil moisture). At hourly to daily timescales, the CH₄ fluxes were sensitive to rainfall, probably because CH₄ emission increased and/or absorption decreased during and after rainfall. The observed canopy-scale fluxes showed complex behaviours beyond those expected from previous plot-scale measurements and the CH₄ fluxes changed from sink to source and vice versa.  相似文献   

Crustal Structure Beneath Lofoten, N. Norway, From Vertical Incidence and Wide-Angle Seismic Data   总被引：1，自引：0，他引：1  

R. Mjelde  M. A. Sellevoll  H. Shimamura  T. Iwasaki  T. Kanazawa 《Geophysical Journal International》1993,114(1):116-126

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Ocean bottom tiltmeter with acoustic data retrieval system implanted by a submersible     

Hideki Shimamura  Toshihiko Kanazawa 《Marine Geophysical Researches》1988,9(3):237-254

Sensitive Ocean Bottom Implanted Tiltmeters (OBITs) with a sophisticated data retrieval system have been developed in order to observe directly the subduction of oceanic lithosphere. The OBIT is the first long-term geophysical instrument which was designed to be deployed by a manned deep-sea submersible. When the OBIT is put on oceanic lithosphere which is bending and is about to subduct under a deep sea trench, the OBIT records the subduction by observing the tilt of the surface of the lithosphere. The OBIT system has a sensitivity of 10^-8 radian, which is enough to detect the ongoing subduction in months or years. The OBIT may give an answer to the question whether there are fluctuations in the subduction rate.Two OBITs were successfully deployed on a seaward slope of the Kuril Trench by the newly built French deep submersible, Nautile. The OBITs were installed on the northwest shoulder of Erimo seamount, at a depth of 3930 m, in the Kuril Trench. In order to attain stable long-term observations of crustal deformations, the sensing unit was cemented onto bare rock by mortar. We have not yet had an opportunity to recover the data.The life of the instruments is expected to be more than five years. An acoustic data transmission system has been developed for the OBIT data recovery. The stored data can be retrieved at any moment during the observation period, with no need to retrieve the instruments nor to interrupt the observation, by use of the acoustic system. The acoustic system has a high data transmission rate as well as extremely low power consumption. This will be the first long-term crustal deformation measurement on the sea floor.  相似文献   

Occurrence of coprostanol, 24-ethylcoprostanol and 5α-stanols in the marine sediments     

Shin-ichi Teshima  Akio Kanazawa 《Journal of Oceanography》1978,34(3):85-92

The present study deals with the elucidation of sterol composition of the marine sediments in Kagoshima Bay. The identification of each sterol was performed by gas-liquid chromatography, Ag⁺ impregnated column chromatography, mass spectrometry, and nuclear magnetic resonance spectrometry. The sediment obtained near the estuary of River Koutsuki contained large portions of 5-stanols such as coprostanol and 24-ethylcoprostanol basides 5-stanols such as cholestanol, 24-methylcholestanol, and 24-ethylcholestanol in the sterol fraction. These 5-stanols in the marine sediment may be derived from the fecal contamination by domestic sewages.  相似文献   

The ocean/continent transition along a profile through the Lofoten basin,Northern Norway     

Andreas Goldschmidt-Rokita  Knut J. F. Hansch  Hans B. Hirschleber  Takaya Iwasaki  Toshihiko Kanazawa  Hideki Shimamura  Markvard A. Sellevoll 《Marine Geophysical Researches》1994,16(3):201-224

The Cenozoic margins of the Norwegian-Greenland Sea offer ideal conditions for passive margin studies. A series of structural elements, first observed on these margins, led to the concept of volcanic passive margins. Questions still remain about the development of such features and the location of the boundary between oceanic and continental crust. Despite the thin sediment cover of the margins, seismic reflection data are not able to image the deeper structures due to the occurrence of igneous rocks at shallow depth.This paper presents a 320-km long profile perpendicular to the strike of the main structural units of the Lofoten Margin in Northern Norway. A geological model is proposed, based on observations made with ocean bottom seismographs, which recorded seismic refraction data and wide angle reflections, along with a seismic reflection profile covering the same area. Ray-tracing was used to calculate a geophysical model from the shelf area into the Lofoten basin. The structures typical of a volcanic passive margin were found, showing that the Lofoten Margin was influenced by increased volcanic activity during its evolution. The ocean/continent transition is located in a 30-km wide zone landwards of the Vøring Plateau escarpment.The whole margin is underlain by a possibly underplated, high velocity layer. Evidence for a pre-rift sediment basin landwards of the escarpment, overlain by basalt flows, was seen. These structural features, related to extensive volcanism on the Lofoten Margin, are not as distinct as further south along the Norwegian Margin. Viewed in the light of the hot-spot theory of White and McKenzie (1989) the Lofoten Margin can be interpreted as a transitional type between volcanic and non-volcanic passive margin.  相似文献   

Precise Positioning of Ocean Bottom Seismometer by Using Acoustic Transponder and CTD   总被引：1，自引：0，他引：1  

Shiobara  Hajime  Nakanishi  Ayako  Shimamura  Hideki  Mjelde  Rolf  Kanazawa  Toshihiko  Berg  Eivind W. 《Marine Geophysical Researches》1997,19(3):199-209

We have obtained precise estimates of the position of Ocean Bottom Seismometers (OBS) on the sea bottom. Such estimates are usually uncertain due to their free falling deployment. This uncertainty is small enough, or is correctable, with OBS spacing of more than 10 km usually employed in crustal studies. But, for example, if the spacing is only 200 m for OBS reflection studies, estimates of the position with an accuracy of the order of 10 m or more is required.The determination was carried out with the slant range data, ship position data and a 1D acoustic velocity structure calculated from Conductivity–Temperature–Depth (CTD) data, if they are available. The slant range data were obtained by an acoustic transponder system designed for the sinker releasing of the OBS or travel time data of direct water wave arrivals by airgun shooting. The ship position data was obtained by a single GPS or DGPS. The method of calculation was similar to those used for earthquake hypocenter determination.The results indicate that the accuracy of determined OBS positions is enough for present OBS experiments, which becomes order of 1 m by using the DGPS and of less than 10 m by using the single GPS, if we measure the distance from several positions at the sea surface by using a transponder system which is not designed for the precise ranging. The geometry of calling positions is most important to determine the OBS position, even if we use the data with larger error, such as the direct water wave arrival data. The 1D acoustic velocity structure should be required for the correct depth of the OBS. Although it is rare that we use a CTD, even an empirical velocity structure works well.  相似文献   

Mobility spectrometry of the atmospheric ions in relation to atmospheric pollution     

M. Misaki  M. Ohtagaki  I. Kanazawa 《Pure and Applied Geophysics》1972,100(1):133-145

Summary The dynamic spectra of the atmospheric ions with mobilities between 3.2×10^–4 m²/V sec and 1.3×10^–8 m²/V sec were obtained in the clean and the polluted atmosphere. Based on the results, the size spectra of the submicron aerosols were deduced which show that the distribution function in Junge's expression increases in proportion to the radius of particle. Very rapid progress of the atmospheric pollution by the submicron aerosols was inferred at a rural country. The concentration of submicron aerosol particles at the site was found to have been increasing at the rate of being doubled every three years since 1964.

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Zusammenfassung Die dynamischen Spektren atmosphärischer Ionen, deren Beweglichkeiten zwischen 3.2·10^–4 m²/(V sec) und 1.3·10^–8 m²/(V sec) lagen, wurden in reiner und verschmutzter Luft gemessen. Auf der Grundlage dieser Messergebnisse wurden die Grössenspektren der Aerosolteilchen mit Radien unterhalb 10^–6 m abgeleitet. Sie zeigen dass die verteilungsfunktion in der Formel von Junge im Verhältnis zum Teilchenradius anwächst. Sehr starkes Anwachsen der Verschmutzung durch so kleine Teilchen wurde in einer ländlichen Umgebung festgestellt. Es wurde gefunden, dass seit 1964 die Zahl der Verschmutzungsteilchen dieser Grösse an der Messtelle alle drei Jahre sich verdoppelt hat.

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