Effects of wind on radiation spectra from magnetized accretion discs     

Naohiro Yamazaki  Osamu Kaburaki†  Motoki Kino 《Monthly notices of the Royal Astronomical Society》2002,337(4):1357-1367

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High-temperature and high-pressure equation of state for the hexagonal phase in the system NaAlSiO4 – MgAl2O4     

T. Shinmei  T. Sanehira  D. Yamazaki  T. Inoue  T. Irifune  K. Funakoshi  A. Nozawa 《Physics and Chemistry of Minerals》2005,32(8-9):594-602

Thermal equation of state of an Al-rich phase with Na_1.13Mg_1.51Al_4.47Si_1.62O₁₂ composition has been derived from in situ X-ray diffraction experiments using synchrotron radiation and a multianvil apparatus at pressures up to 24 GPa and temperatures up to 1,900 K. The Al-rich phase exhibited a hexagonal symmetry throughout the present pressure–temperature conditions and the refined unit-cell parameters at ambient condition were: a=8.729(1) Å, c=2.7695(5) Å, V ₀=182.77(6) Å³ (Z=1; formula weight=420.78 g/mol), yielding the zero-pressure density ρ₀=3.823(1) g/cm³ . A least-square fitting of the pressure-volume-temperature data based on Anderson’s pressure scale of gold (Anderson et al. in J Appl Phys 65:1534–543, 1989) to high-temperature Birch-Murnaghan equation of state yielded the isothermal bulk modulus K ₀=176(2) GPa, its pressure derivative K ₀ ^′ =4.9(3), temperature derivative (?K _T /?T) _P =?0.030(3) GPa K^?1 and thermal expansivity α(T)=3.36(6)×10^?5+7.2(1.9)×10^?9 T, while those values of K ₀=181.7(4) GPa, (?K _T /?T) _P =?0.020(2) GPa K^?1 and α(T)=3.28(7)×10^?5+3.0(9)×10^?9 T were obtained when K ₀ ^′ was assumed to be 4.0. The estimated bulk density of subducting MORB becomes denser with increasing depth as compared with earlier estimates (Ono et al. in Phys Chem Miner 29:527–531 2002; Vanpeteghem et al. in Phys Earth Planet Inter 138:223–230 2003; Guignot and Andrault in Phys Earth Planet Inter 143–44:107–128 2004), although the difference is insignificant (<0.6%) when the proportions of the hexagonal phase in the MORB compositions (～20%) are taken into account.  相似文献   

Seismic microzonation of the greater Bangkok area using microtremor observations     

Rabin Tuladhar  Fumio Yamazaki  Pennung Warnitchai  Jun Saita 《地震工程与结构动力学》2004,33(2):211-225

Bangkok, the capital city of Thailand, is located at a remote distance from seismic sources. However, it has a substantial risk from these distant earthquakes due to the ability of the underlying soft clay to amplify ground motions. It is therefore imperative to conduct a detailed seismic hazard assessment of the area. Seismic microzonation of big cities, like Bangkok, provides a basis for site‐specific hazard analysis, which can assist in systematic earthquake mitigation programs. In this study, a seismic microzonation map for the greater Bangkok area is constructed using microtremor observations. Microtremor observations were carried out at more than 150 sites in the greater Bangkok area. The predominant periods of the ground were determined from the horizontal‐to‐vertical (H/V) spectral ratio technique. A microzonation map was then developed for the greater Bangkok area based on the observations. Moreover, the transfer functions were calculated for the soil profile at eight sites, using the computer program SHAKE91, to validate the results from the microtremor analysis. The areas near the Gulf of Thailand, underlaid by a thick soft clay layer, were found to have long natural periods ranging from 0.8s to 1.2s. However, the areas outside the lower central plain have shorter predominant periods of less than 0.4s. The study shows that there is a great possibility of long‐period ground vibration in Bangkok, especially in the areas near the Gulf of Thailand. This may have severe effects on long‐period structures, such as high‐rise buildings and long‐span bridges. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Normal faulting of the Daiichi-Kashima Seamount in the Japan Trench revealed by the Kaiko I cruise, Leg 3     

Kazuo Kobayashi  Jean-Paul Cadet  Jean Aubouin  Jacques Boulgue  Jacques Dubois  Roland von Huene  Laurent Jolivet  Toshihiko Kanazawa  Junzo Kasahara  Kin-ichiro Koizumi  Serge Lallemand  Yasuo Nakamura  Guy Pautot  Kiyoshi Suyehiro  Shin Tani  Hidekazu Tokuyama  Toshitsugu Yamazaki 《Earth and Planetary Science Letters》1987,83(1-4)

A detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern Japan Trench, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2–4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and single-channel seismic reflection records. Vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported. The northern and southern extensions of the normal fault beyond the flank of the seamount were delineated. Materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount. Canyons observed in the upper landward slope terminate at the mid-slope terrace which has been uplifted since start of subduction of the seamount. Most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern Japan Trench wall. This survey was conducted on R/V “Jean Charcot” as a part of the Kaiko I cruise, Leg 3, in July–August 1984 under the auspices of the French-Japanese scientific cooperative program.  相似文献   

Asymmetric rifting of the northern Mariana Trough   总被引：3，自引：0，他引：3  

Toshitsugu  Yamazaki & Fumitoshi  Murakami 《Island Arc》1998,7(3):460-470

The evolution of rifting in the northern Mariana Trough was studied, based on single-channel seismic reflection profiles and heat flow. The rift showed structural asymmetry. The northernmost part of the Mariana Trough at 24°N, just south of Minami-Iwojima Island, is now in an incipient rifting stage and shows a half-graben structure. The arc crust just behind the volcanic front is cut by a few major east-dipping normal faults. The major faults extend southward behind the Hiyoshi seamounts around 23°30'N. The rift develops to a full-graben stage at ∼ 23°N, where the width of the trough increases to 80 km. The trough is comprised of several faulted and tilted blocks of island-arc crust. Maximum subsidence occurs along a row of small grabens on the eastern margin of the trough. These grabens are separated by arc volcanoes, and their depths increase southward from 2500 m at 23°20'N to 4500 m at 22°N. The strike of each graben is north-northwest–south-southeast, which is close to the trend of the remnant West Mariana Ridge, but oblique to the active Mariana arc. Crustal extension becomes concentrated along the eastern margin of the trough as rifting progresses. The transition from rifting to sea floor spreading may occur at ∼ 22°N, where the width of the trough is ∼ 120 km. The possible spreading center lies along the southern extension of the grabens on the eastern margin. The period of back-arc rifting before spreading begins is estimated to be less than 3 million years. Heat flow is asymmetric in the rift. High heat flow was observed only in or close to the row of grabens along the eastern margin of the trough. The asymmetric pure shear extension model fits the observed heat flow distribution better than the simple shear extension model.  相似文献   

Tectonoelectricity     

Yoshio Yamazaki 《Surveys in Geophysics》1977,3(2):123-142

Anomalous earth-current changes in association with an earthquake occurrence have often been reported since the 19th century. Changes reported in classical as well as recent literature are reviewed, although it is hard to say that any physically clear relationship between earth-current changes and earthquakes has been established. Even though a strong correlation between precursory earthcurrent changes and earthquakes has often been reported in the U.S.S.R. and the People's Republic of China in recent years, it appears that a general rule governing the earthquake-related earth-current changes is still very much unknown, partly because of contamination by artificial and natural noise.In contrast to the difficulty in understanding earth-current changes, monitoring of earth-resistivity seems to provide a much clearer means for interpreting geoelectric phenomena in association with tectonic processes in the Earth. Soviet and American work showed that the resistivity decreases to a considerable extent in the focal region prior to an earthquake. Such a change seems to be closely correlated to dilatancy generation in the Earth's crust. This finding doubtless provides an important means for earthquake prediction.An ususual, highly sensitive resistivity variometer, developed by the writer, disclosed that a resistivity change takes place at a teleseismic distance when an earthquake of large and medium magnitude occurs. Many of the resistivity changes thus observed are preceded by a premonitory change, which is supposed to reflect the preliminary rupture at a focal region.  相似文献   

Precursory and coseismic resistivity changes     

Y. Yamazaki 《Pure and Applied Geophysics》1975,113(1):219-227

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Textural analysis and flow mechanism of the Donzurubo subaqueous pyroclastic flow deposits     

T. Yamazaki  I. Kato  I. Muroi  M. Abe 《Bulletin of Volcanology》1973,37(2):231-244

The Donzurubo subaqueous pyroclastic flow deposits deposited in subaqueous environments maintaining high temperatures (about 500°C). Each flow unit of these pyroclastic flow deposits shows some characteristic size distributions in its stratigraphic column. The concentration of pumice at the top clearly defines the top facies of a flow unit. Median diameter (Md Ø) and the averages of the largest ten essential dense debris increase gradually starting from both the top and the bottom of the flow unit. The maximum points of Md Ø and the averages of the largest ten essential dense debris are usually found in the middle zone of each flow unit, but the Md Ø maximum points are generally in a lower position than the averages. Mechanical analyses show that the deposits consist of polymodal populations. They show, on the whole, an asymmetrical distribution, which is mainly due to the absence of the coarser fractions of the main population. The size distribution characteristics and the C-M pattern of the deposits suggest that these subaqueous pyroclastic flow deposits were not originated by homogeneously suspended turbulent flows but by incandescent turbulent flows with layered suspension.  相似文献   

Coseismic resistivity steps     

Y. Yamazaki 《Tectonophysics》1974,22(1-2)

A resistivity variometer, which has been operated at a station about 60 km south of Tokyo, recorded eleven resistivity steps in association with earthquake occurrences during a four year period of observation. Comparing these steps to those calculated on the basis of the dislocation theory, it is concluded that the variometer has an enormously high sensitivity or amplification factor amounting to 3 · 10⁴ for small strains of the order of 10⁻⁸–10⁻⁹.Hypothetical strain steps, that would have been observed at a point having an epicentral distance of 100 km, correlate well with earthquakes of magnitudes ranging from 5 to 8. The time required for a step to be completed seems large for a large earthquake although there is considerable scatter in the diagram for the time vs. magnitude relation. Nothing definite has been put forward about the nature of precursory effect observed for a few of the earthquakes.  相似文献   

Correlation of JMA instrumental seismic intensity with strong motion parameters     

Kazi R. Karim  Fumio Yamazaki 《地震工程与结构动力学》2002,31(5):1191-1212

The Japan Meteorological Agency (JMA) seismic intensity (I_JMA) has been used as a measure of strong shaking for many years in Japan, and it necessitates to know the correlation between the JMA seismic intensity and other strong motion indices, e.g. Peak Ground Acceleration (PGA), Peak Ground Velocity (PGV), and Spectrum Intensity (SI). In this study, two strong motion data sets were selected; in which, the first set consists of 879 three‐components non‐liquefied records selected from 13 major earthquake events that occurred in Japan, the United States, and Taiwan, and the second set consists of 17 liquefied records selected from 7 major earthquake events that occurred in Japan and the United States. The JMA seismic intensity and other ground motion indices were calculated using the selected data sets. The relationships between the JMA seismic intensity and PGA, PGV, and SI were then derived performing a two‐stage linear regression analysis. Results from the analysis show that the JMA instrumental seismic intensity shows higher correlation with SI than PGA or PGV, and it shows the highest correlation with the parameters such as the combination of PGA and SI or the product of PGA and SI. The obtained relationships are also compared with the ones obtained by other studies, which may be useful for the disaster management agencies in Japan and deployment of new SI‐sensors that monitor both PGA and SI. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献