Vibration characteristics of rigid body placed on sand ground     

Y. -S. Kim  K. Miura  S. Miura  M. Nishimura 《Soil Dynamics and Earthquake Engineering》2001,21(1)

This study aims to investigate experimentally the vibration properties of rigid body placed on sand ground surface. The rigid body models with circular or rectangular base with variable mass, inertial moment and base sizes, were prepared, and the vibration behavior was observed in some series of free vibration tests and forced vibration tests. The observed behavior was analyzed and the vibration mode, vibration period and damping ratio were examined. It was found that the natural vibration period depends not only on the mechanical properties of rigid body and ground, but also on the magnitude of vibration amplitude. This suggested the notable effect of nonlinear strain dependent stiffness of ground material. A physical model with distributed spring–dashpot element was used to model the interactive mechanical behavior between rigid body and ground. The stiffness of the spring–dashpot element was evaluated through the modal analysis of the observed vibration behaviors. The effects of base shape, base size and base pressure on the stiffness of spring–dashpot element are discussed. The spring–dashpot model was verified with the behavior observed in forced vibration tests.  相似文献   

Construction of GPS MonitoringNetwork,Characteristics of RecentCrustal Movement,and Relationbetween Stress Field andEarthquake Activity in the NingxiaRegion     

Xu Wenjun  Zhao　Weiming  Chai Chizhang  Jin Yanlong  Sun Lixin  Zheng Sihu  Satoshi Miura 《中国地震研究》2001,15(3):252-265

INT正ODU**!0厂Nln以la Is located In the nol’th segmentdthe North－southselsnuc Belt,Whlchls thejuncturedthe Qinghai－Xizang(Dbet)block,Alxa block and Odos block．In that region,the tectonic activity。svery strong;。y strong earthquakes occu。d In history,such as the 1739 ingluo M。8．0 earthqu拙eandl920 Halyuan M。8．5 eafthquake,etc．; Merately strongeaFthquakes are still veryactlve atpresent,onlyln the Wuzhong－un斟m area,there have been7 e血hquakes tvlth M。＞5．0 to occ…  相似文献   

Numerical analysis of shipping water impact on a deck using a particle method     

Kazuya Shibata  Seiichi Koshizuka   《Ocean Engineering》2007,34(3-4):585-593

The objective of this study is to simulate three-dimensional behavior of shipping water and to predict the impact pressure on the deck using a particle method. An experiment carried out in a two-dimensional wave tank with a fixed deck model was numerically analyzed in three dimensions. The fluid motion, the surface elevation, and the impact pressure on the deck were compared between the experiment and the calculation and good agreement was obtained.  相似文献   

Noble gas and oxygen isotope studies of aubrites: A clue to origin and histories     

Yayoi N. Miura  Hiroshi Hidaka  Minoru Kusakabe 《Geochimica et cosmochimica acta》2007,71(1):251-270

Noble gas measurements were performed for nine aubrites: Bishopville, Cumberland Falls, Mayo Belwa, Mount Egerton, Norton County, Peña Blanca Spring, Shallowater, ALHA 78113 and LAP 02233. These data clarify the origins and histories, particularly cosmic-ray exposure and regolith histories, of the aubrites and their parent body(ies). Accurate cosmic-ray exposure ages were obtained using the ⁸¹Kr-Kr method for three meteorites: 52 ± 3, 49 ± 10 and 117 ± 14 Ma for Bishopville, Cumberland Falls and Mayo Belwa, respectively. Mayo Belwa shows the longest cosmic-ray exposure age determined by the ⁸¹Kr-Kr method so far, close to the age of 121 Ma for Norton County. These are the longest ages among stony meteorites. Distribution of cosmic-ray exposure ages of aubrites implies 4-9 break-up events (except anomalous aubrites) on the parent body. Six aubrites show “exposure at the surface” on their parent body(ies): (i) neutron capture ³⁶Ar, ⁸⁰Kr, ⁸²Kr and/or ¹²⁸Xe probably produced on the respective parent body (Bishopville, Cumberland Falls, Mayo Belwa, Peña Blanca Spring, Shallowater and ALHA 78113); and/or (ii) chondritic trapped noble gases, which were likely released from chondritic inclusions preserved in the aubrite hosts (Cumberland Falls, Peña Blanca Spring and ALHA 78113). The concentrations of ¹²⁸Xe from neutron capture on ¹²⁷I vary among four measured specimens of Cumberland Falls (0.5-76 × 10⁻¹⁴ cm³STP/g), but are correlated with those of radiogenic ¹²⁹Xe, implying that the concentrations of (¹²⁸Xe)_n and (¹²⁹Xe)_rad reflect variable abundances of iodine among specimens. The ratios of (¹²⁸Xe)_n/(¹²⁹Xe)_rad obtained in this work are different for Mayo Belwa (0.045), Cumberland Falls (0.015) and Shallowater (0.001), meaning that neutron fluences, radiogenic ¹²⁹Xe retention ages, or both, are different among these aubrites. Shallowater contains abundant trapped Ar, Kr and Xe (2.2 × 10⁻⁷, 9.4 × 10⁻¹⁰ and 2.8 × 10⁻¹⁰ cm³STP/g, respectively) as reported previously (Busemann and Eugster, 2002). Isotopic compositions of Kr and Xe in Shallowater are consistent with those of Q (a primordial noble gas component trapped in chondrites). The Ar/Kr/Xe compositions are somewhat fractionated from Q, favoring lighter elements. Because of the unbrecciated nature of Shallowater, Q-like noble gases are considered to be primordial in origin. Fission Xe is found in Cumberland Falls, Mayo Belwa, Peña Blanca Spring, ALHA 78113 and LAP 02233. The majority of fission Xe is most likely ²⁴⁴Pu-derived, and about 10-20% seems to be ²³⁸U-derived at ¹³⁶Xe. The observed (¹³⁶Xe)_Pu corresponds to 0.019-0.16 ppb of ²⁴⁴Pu, from which the ²⁴⁴Pu/U ratios are calculated as 0.002-0.009. These ratios resemble those of chondrites and other achondrites like eucrites, suggesting that no thermal resetting of the Pu-Xe system occurred after ∼4.5 Ga ago. We also determined oxygen isotopic compositions for four aubrites with chondritic noble gases and a new aubrite LAP 02233. In spite of their chondritic noble gas signatures, oxygen with chondritic isotopic compositions was found only in a specimen of Cumberland Falls (Δ¹⁷O of ∼0.3‰). The other four aubrites and the other two measured specimens of Cumberland Falls are concurrent with the typical range for aubrites.  相似文献   

Seismological structure and implications of collision between the Ontong Java Plateau and Solomon Island Arc from ocean bottom seismometer–airgun data     

Seiichi Miura  Kiyoshi Suyehiro  Masanao Shinohara  Narumi Takahashi  Eiichiro Araki  Asahiko Taira   《Tectonophysics》2004,389(3-4):191

A seismic refraction–reflection experiment using ocean bottom seismometers and a tuned airgun array was conducted around the Solomon Island Arc to investigate the fate of an oceanic plateau adjacent to a subduction zone. Here, the Ontong Java Plateau is converging from north with the Solomon Island Arc as part of the Pacific Plate. According to our two-dimensional P-wave velocity structure modeling, the thickness of the Ontong Java Plateau is about 33 km including a thick (15 km) high-velocity layer (7.2 km/s). The thick crust of the Ontong Java Plateau still persists below the Malaita Accreted Province. We interpreted that the shallow part of the Ontong Java Plateau is accreted in front of the Solomon Island Arc as the Malaita Accreted Province and the North Solomon Trench are not a subduction zone but a deformation front of accreted materials. The subduction of the India–Australia Plate from the south at the San Cristobal Trench is confirmed to a depth of about 20 km below sea level. Seismicity around our survey area shows shallow (about 50 km) hypocenters from the San Cristobal Trench and deep (about 200 km) hypocenters from the other side of the Solomon Island Arc. No earthquakes occurred around the North Solomon Trench. The deep seismicity and our velocity model suggest that the lower part of the Ontong Java Plateau is subducting. After the oceanic plateau closes in on the arc, the upper part of the oceanic plateau is accreted with the arc and the lower part is subducted below the arc. The estimation of crustal bulk composition from the velocity model indicates that the upper portion and the total of the Solomon Island Arc are SiO₂ 58% and 53%, respectively, which is almost same as that of the Izu–Bonin Arc. This means that the Solomon Island Arc can be a contributor to growing continental crust. The bulk composition of the Ontong Java Plateau is SiO₂ 49–50%, which is meaningfully lower than those of continents. The accreted province in front of the arc is growing with the convergence of the two plates, and this accretion of the upper part of the oceanic plateau may be another process of crustal growth, although the proportion of such contribution is not clear.  相似文献   

Evidence of Microbial Activity in the Formation of Manganese Wads at the Asahidake Hot Spring in Hokkaido, Japan     

Naoki Mita  Hiroyuki Miura 《Resource Geology》2003,53(3):233-238

Abstract. Mt. Asahidake is an active volcano, with more than 90 active wells, in the Daisetsu volcanic group located in central Hokkaido, Japan. Wells along the Yukomanbetsu-sawa River showed high manganese concentrations and associated manganese deposits. These deposits consist of manganese oxides, and the concentration of iron is very low except for one sample collected from the upper reach of the river. Most of the wet samples showed basal diffraction characteristic of todorokite (9.6 Å). Cultivation tests showed that microorganisms were responsible for the oxidation of dissolved Mn²⁺ in the Asahidake hot spring. The dissolved Mn²⁺ concentration in the sterilized hot spring water was unchanged after four days, whereas the Mn²⁺ concentration in the sterilized hot spring water with a small amount of fresh manganese wad was decreased to zero after three days, and manganese oxide formed. This result implies that the activity of microorganism oxidizes dissolved Mn²⁺ and forms manganese oxide at the Asahidake manganese deposits. In addition to Komanoyu hot spring and Yunotaki Falls, this is the third report of microbial activity forming considerable deposits of manganese oxides in hot spring waters.  相似文献   

Measurements of electric charge distribution in volcanic plumes at Sakurajima Volcano,Japan     

Toshiro Miura  Takehiro Koyaguchi  Yoshikazu Tanaka 《Bulletin of Volcanology》2002,64(2):75-93

Measurements of perturbations in the atmospheric potential gradient around volcanic plumes at multiple (from two to five) sites, and measurements of the charge-mass ratio of ash particles falling from volcanic plumes, were carried out at Sakurajima Volcano, Japan. Results from 28 and 29 October 1995, show that the nature of the perturbations depends on the intensity of plume activity. Although plume activity was vigorous on 28 October, negative perturbations were predominant. As plume activity peaked, the magnitude of negative perturbations decreased just below the plume and increased at an off-axis site. During the peak period, positively charged ash particles fell out from the plume. This suggests that the active plume dominantly contained negatively charged materials, and that positively and negatively charged materials were added to the lower and upper parts of the plume, respectively, during the peak period. On the other hand, as plume activity became less vigorous on 29 October, the perturbations were characterized by a positive anomaly followed by a negative anomaly. Because wind velocity increased with altitude that day, we infer that positive and negative charges were distributed in the upper and lower parts of the plume, respectively. The differences in perturbations observed on 28 and 29 October suggest that volcanic plumes are generally composed of three parts: an upper part with positively charged gas and aerosol, a middle part with negatively charged fine ash particles, and a lower part with positively charged coarse ash particles. The compilation of present and previous results from Sakurajima and other volcanoes indicates that the effect of the negative charge in the middle part was predominant in most cases, although positive perturbations caused by the upper part were observed around some weak plumes. The effect of positively charged particles in the lower part was observable only when plume activity was sufficiently strong because positively charged coarse particles tended to fall out near the vent.  相似文献   

Characterization of low-temperature pyroclastic surges that occurred in the northeastern Japan arc during the late 19th century     

Akihiko Fujinawa  Masao Ban  Tsukasa Ohba  Kazuo Kontani  Kotaro Miura 《Journal of Volcanology and Geothermal Research》2008

Three eruption events occurring in the central part of the northeastern Japan arc were investigated and compared: Adatara AD1900, Zao AD1895, and Bandai AD1888. Producing low-temperature (LT) pyroclastic surges, these events are characterized by steam eruptions ejecting no juvenile material. These eruptions' well-preserved eruptive deposits and facies facilitated granulometric analyses of the beds, which revealed the transport and deposition mechanisms of LT surges. Combining these results with those of investigations of documents reporting the events, we correlated each eruption to the relevant individual bed and reconstructed the LT surge development sequence. Important findings related to the transport and deposition modes are the following. (1) Bed sets consisting of thin, laminated ash and its overlying thick massive tuff were recognized in the Adatara 1900 proximal deposits. The bed set was probably produced by a strong wind that discharged and propagated quickly from the vent (leading wind) and a gravitationally segregated, highly concentrated flow originated from the eruption column, within a discrete eruption episode. A similar combination might have occurred during the first surge of the Bandai 1888 event. (2) Comparison of the proximal and distal facies for the largest eruption of Adatara 1900 event indicates that the initial turbulence of the eruption cloud decreased rapidly, transforming into a density-stratified surge with a highly concentrated part near the base. Similar surges occurred in the climatic stage of Zao 1895. (3) Bandai 1888 ejecta indicate massive beds deposited preferentially at topographic lows. Co-occurring planar beds showed no topographic affection, as indicated by the topographic blocking of a stratified surge. The observed facies–massive tuffs, crudely stratified tuffs, and thin bedded tuffs–are compatible with those for high-temperature surges. At Bandai, absence of dune bedded tuffs and commonly poorer sorting in the LT surge deposits might be attributable to poor thermally induced turbulence of eruption columns. Condensation of vapor in the surges might have contributed to the poor sorting. The estimated explosion energies were 6 × 10¹³ J for Adatara AD1900, 6.5 × 10¹⁰ J for Zao AD1895, and 6.5 × 10¹⁵ J for Bandai AD1888, implying that the three events were hydrothermal eruptions with distinctive eruptive mechanisms. Regarding eruption sources, the Adatara 1900 event was caused solely by thermal energy of the hydrothermal fluid, although magma intrusion likely triggered evolution of hydrothermal systems at Zao in 1895. Steam eruptions in the Bandai 1888 event occurred simultaneously with sudden exposure of the hydrothermal system, whose triggers require no internal energy.  相似文献   

Improving GPS positioning estimates during extreme weather situations by the help of fine-mesh numerical weather models     

Thomas Hobiger  Seiichi Shimada  Shingo Shimizu  Ryuichi Ichikawa  Yasuhiro Koyama  Tetsuro Kondo 《Journal of Atmospheric and Solar》2010,72(2-3):262-270

Space geodetic applications require to model troposphere delays as good as possible in order to achieve highly accurate positioning estimates. However, these models are not capable to consider complex refractivity fields which are likely to occur during extreme weather situations like typhoons, storms, heavy rain-fall, etc. Thus it has been investigated how positioning results can be improved if information from numerical weather models is taken into account. It will be demonstrated that positioning errors can be significantly reduced by the usage of ray-traced slant delays. Therefore, meso-scale and fine-mesh numerical weather models are utilized and their impact on the positioning results will be measured. The approach has been evaluated during a typhoon passage using global positioning service (GPS) observations of 72 receivers located around Tokyo, proving the usefulness of ray-traced slant delays for positioning applications. Thereby, it is possible reduce virtual station movements as well as improve station height repeatabilities by up to 30% w.r.t. standard processing techniques. Additionally the advantages and caveats of numerical weather models will be discussed and it will be shown how fine-mesh numerical weather models, which are restricted in their spatial extent, have to be handled in order to provide useful corrections.  相似文献   

High resolution OSL dating back to MIS 5e in the central Sea of Okhotsk   总被引：1，自引：0，他引：1  

Saiko Sugisaki  Jan-Pieter Buylaert  Andrew Murray  Sumiko Tsukamoto  Yoshifumi Nogi  Hideki Miura  Saburo Sakai  Koichi Iijima  Tatsuhiko Sakamoto 《Quaternary Geochronology》2010,5(2-3):293-298

Marine sediments contain important archives of past ocean and climate changes, but at high latitudes the absence of carbonate has prevented the construction of accurate chronological models. We have begun a study to (1) determine the accuracy of luminescence ages in deep-sea marine sediments, e.g. by comparison with marine oxygen isotope stratigraphy where possible, (2) describe changes in sedimentation rate through time, and (3) test whether it is possible to date back to marine isotope stage 5e (MIS 5e). We show here that optical dating of fine grains of quartz from the central Sea of Okhotsk is able to provide an accurate and precise chronology for the reconstruction of the palaeoceanic and palaeoclimatic environment at our site. The upper 6.5 m of the 18.42 m long core MR0604-PC07A is believed, based on its magnetic susceptibility and the oxygen isotope (δ¹⁸O) records to contain the last ～150 ka. Forty OSL samples were taken from this upper part of the core. The single-aliquot regenerative-dose (SAR) procedure is used for equivalent dose (D_e) determination. The luminescence characteristics of fine-grained quartz (4–11 μm) extracted from the core are described. The OSL signal is dominated by the fast component and a dose recovery test shows that we can accurately measure a known dose given in the laboratory prior to any heat treatment. Dose rates were determined using high-resolution gamma spectrometry, and vary between 0.4 and 1.6 Gy/ka. The OSL ages from this section lie between ～140 ka and ～15 ka and are in very good agreement with the δ¹⁸O stratigraphy up to MIS 5e. A clear change in sedimentation rate is identified: between ～139 and 110 ka, the sedimentation rate was ～0.09 m/ka, but then from ～110 to 15 ka, the sedimentation rate decreases to a constant value of ～0.04 m/ka. Our data confirm that OSL dating using widely distributed fine-grain quartz has great potential for dating deep-sea sediments. Because luminescence methods use clastic materials, they do not depend on the presence of biogenic carbonate. As a result it is now likely that we can establish a chronology in regions of the ocean that were previously undatable.  相似文献