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51.
Koki Aizawa Wataru Kanda Yasuo Ogawa Masato Iguchi Akihiko Yokoo Hiroshi Yakiwara Takayuki Sugano 《Journal of Volcanology and Geothermal Research》2011,199(1-2):165-175
Continuous magnetotelluric (MT) measurements were conducted from May 2008 to July 2009 at Sakurajima, one of the most active volcanoes in Japan. Two observation sites were established at locations 3.3 km east and 3 km west–northwest of the summit crater. At both observation sites, the high-quality component of the impedance tensor (Zyx) showed variations in apparent resistivity of approximately ± 20% and phase change of ± 2°, which continued for 20–180 days in the frequency range between 320 and 4 Hz. The start of the period of changes in apparent resistivity approximately coincided with the start of uplift in the direction of the summit crater, as observed by a tiltmeter, which is one of the most reliable pieces of equipment with which to detect magma intrusion beneath a volcano. A 2D inversion of MT impedance suggests that the resistivity change occurred at a depth around sea level. One of the possible implications of the present finding is that the degassed volatiles migrated not only vertically through the conduit but also laterally through a fracture network, mixing with shallow groundwater beneath sea level and thereby causing the observed resistivity change. 相似文献
52.
Abstract— Mn‐Cr systematics in phosphates (sarcopside, graftonite, beusite, galileiite, and johnsomervilleite) in IIIAB iron meteorites were investigated by secondary ion mass spectrometry (SIMS). In most cases, excesses in 53Cr are found and δ53Cr is well correlated with Mn/Cr ratios, suggesting that 53Mn was alive at the time of IIIAB iron formation. The inferred Mn‐Cr “ages” are different for different phosphate minerals. This is presumably due to a combined effect of the slow cooling rates of IIIAB iron meteorites and the difference in the diffusion properties of Cr and Mn in the phosphates. The ages of sarcopside are the same for the IIIAB iron meteorites. Johnsomervilleite shows apparent old ages, probably because of a gain of Cr enriched in 53Cr during the closure process. Apparently, old Mn‐Cr ages reported in previous studies can also be explained in a similar way. Therefore, the IIIAB iron meteorites probably experienced identical thermal histories and thus derived from the core of a parent body. Thermal histories of the parent body of IIIAB iron meteorites that satisfy the Mn‐Cr chronology and metallographic cooling rates were constructed by computer simulation. The thermal history at an early stage (<10 Ma after CAI formation) is well determined, though later history may be more model‐dependent. It is suggested that relative timing of various events in the IIIAB parent body may be estimated with the aid of the thermal history. There is a systematic difference in Mn and Cr concentrations in various minerals (phosphates, sulfide, etc.) among the IIIAB iron meteorites, which seems to be mainly controlled by redox conditions. 相似文献
53.
New and previous versions of the high-resolution 20- and 60-km-mesh Meteorological Research Institute atmospheric general circulation models are used to investigate potential future changes in tropical cyclone (TC) activity in the North Indian Ocean (NIO). Fifteen ensemble experiments are performed under the International Panel on Climate Change A1B scenario. Most of the ensemble future (2075–2099) experiments do not project significant future changes in the basin-scale TC genesis number; however, they commonly show a substantial increase (by 46 %) in TC frequency over the Arabian Sea and a decrease (by 31 %) in the Bay of Bengal. Projected future changes in TC genesis frequency show a marked seasonal variation in the NIO: a significant and robust reduction during the pre-monsoon season, an increase during the peak-monsoon season, and a westward shift during the post-monsoon season. Several large-scale thermodynamic and dynamical parameters are analysed to elucidate the physical mechanism responsible for the future changes in TC activity; this analysis reveals a seasonal dependence of the relative contribution of these parameters to the projected future changes in TC genesis frequency. 相似文献
54.
Masato Kobiyama Aline de Almeida Mota Fernando Grison Joana Nery Giglio 《Natural Hazards》2011,59(2):1077-1086
The rainfall events that occurred in the Cubat?o do Norte River watershed, Santa Catarina State, Brazil, in 2008, were characterized
by both high intensities and amounts and triggered landslides in this watershed. The objective of the present study was to
analyze the influence of landslides on the turbidity and the total solid concentration (TS) in this river using turbidity,
TS, and river discharge data obtained from March 23, 2008, to June 11, 2010. The comparison between turbidity and discharge
patterns implies that the landslide process was not continuous and increased the turbidity intermittently and irregularly.
The sediment yield during the landslide occurrence was approximately five times higher than without the landslide, even though
the discharges were similar. The turbidity/discharge relationship during the landslide occurrence was markedly different from
that before and after the occurrence. The correlation coefficients between turbidity and TS showed that the landslide significantly
changed the sediment yield in this watershed. The result indicates that sediment yield estimations at the watershed level
should be treated more carefully when landslides occur. 相似文献
55.
Horizontal impedance functions of inclined single piles are measured experimentally for model soil-pile systems with both the effects of local soil nonlinearity and resonant characteristics.Two practical pile inclinations of 5° and 10° in addition to a vertical pile embedded in cohesionless soil and subjected to lateral harmonic pile head loadings for a wide range of frequencies are considered.Results obtained with low-to-high amplitude of lateral loadings on model soil-pile systems encased in a laminar shear box show that the local nonlinearities have a profound impact on the horizontal impedance functions of piles.Horizontal impedance functions of inclined piles are found to be smaller than the vertical pile and the values decrease as the angle of pile inclination increases.Distinct values of horizontal impedance functions are obtained for the ’positive’ and ’negative’ cycles of harmonic loadings,leading to asymmetric force-displacement relationships for the inclined piles.Validation of these experimental results is carried out through three-dimensional nonlinear finite element analyses,and the results from the numerical models are in good agreement with the experimental data.Sensitivity analyses conducted on the numerical models suggest that the consideration of local nonlinearity at the vicinity of the soil-pile interface influence the response of the soil-pile systems. 相似文献
56.
57.
Toru Kouyama Takeshi Imamura Masato Nakamura Takehiko Satoh Yoshihumi Futaana 《Planetary and Space Science》2012,60(1):207-216
An improved cloud tracking method for deriving wind velocities from successive planetary images was developed. The new method incorporates into the traditional cross-correlation method an algorithm that corrects for erroneous cloud motion vectors by re-determining the most plausible correlation peak among all of the local maxima on the correlation surface by comparing each vector with its neighboring vectors. The newly developed method was applied to the Venusian violet images obtained by the Solid State Imaging system (SSI) onboard the Galileo spacecraft during its Venus flyby. Although the results may be biased by the choice of spatial scale of atmospheric features, the cloud tracking is the most practical mean of estimating the wind velocities with extensive spatial and temporal coverage. The two-dimensional distribution of the horizontal wind vector field over 5 days was obtained. It was found from these wind maps that the solar-fixed component in 1990 was similar to that in 1982 obtained by the Pioneer Venus orbiter. The deviation of the instantaneous zonal wind field from the solar-fixed component shows a distinct wavenumber-1 structure in the equatorial region. On the assumption that this structure is a manifestation of an equatorial Kelvin wave, the phase relationship between the zonal wind and the cloud brightness suggests a short photochemical lifetime of the violet absorber. The momentum deposition by this Kelvin wave, which is subject to radiative damping, would induce a westward mean-wind acceleration of ~0.3 m s?1 per Earth day. 相似文献
58.
Directionality of ground motions has been discussed in near-source groundmotion study. This is interesting from the point of structural response.Dominance of the fault normal (FN) component has been reported inrelation to fault rupture direction based on the observation recordsobtained in the source area (e.g.. Somerville et al., 1996). The authorsperformed the damage survey of the two Turkey earthquakes in 1999, theKocaeli and the Düzce earthquake, and realized that minaret is a goodtarget to investigate the ground motion directionality, because a minaret isa simple cantilever structure without structural directionality. This paperdescribes the ground motion directionality based on the survey of minaretdamages during the two earthquakes in Turkey. From the damage survey,it is found that the fault normal direction was dominant with a certaindistance from the fault, say, less than 1km. While, at the region withshorter distances, the damage direction was not fault normal but about40° from the fault strike. Discussion is addressed for the specificdamage direction inferred from the minaret damage near the fault. 相似文献
59.
60.
Japan is located at the boundary between three continental and oceanic plates, and there is a great variety and complexity of geological features as a result of tectonic activities. The possibility of excavating large underground tunnels in the seemingly “fragile” rocks in orogenic areas was considered as a national project for the underground storage of petroleum. One hundred and seventy sites in 57 areas were selected based on a comprehensive survey over the whole country. After a successful experiment with a test tunnel, 112 m long and 250 m2 in cross-section area, excavated in Cretaceous granite, three sites in granites and pyroclastic rocks were selected for construction. The largest of these storage tunnels is 550 m in length and20 × 30 m in cross-section.
Before construction, a detailed survey of the subsurface geology was carried out, taking into consideration the structural geology, the mechanical properties of the rocks and the hydrogeology. It was concluded that even in active orogenic areas, there are many suitable sites for large underground excavations and that these can be detected by detailed, planned surveys. 相似文献