Shaking table tests on seismic response of steel braced frames with column uplift     

Mitsumasa Midorikawa  Tatsuya Azuhata  Tadashi Ishihara  Akira Wada 《地震工程与结构动力学》2006,35(14):1767-1785

Previous studies have suggested that rocking vibration accompanied by uplift motion might reduce the seismic damage to buildings subjected to severe earthquake motions. This paper reports on the use of shaking table tests and numerical analyses to evaluate and compare the seismic response of base‐plate‐yielding rocking systems with columns allowed to uplift with that of fixed‐base systems. The study is performed using half‐scale three‐storey, 1 × 2 bay braced steel frames with a total height of 5.3 m. Base plates that yield due to column tension were installed at the base of each column. Two types of base plates with different thicknesses are investigated. The earthquake ground motion used for the tests and analyses is the record of the 1940 El Centro NS component with the time scale shortened by a factor of 1/√2. The maximum input acceleration is scaled to examine the structural response at various earthquake intensities. The column base shears in the rocking frames with column uplift are reduced by up to 52% as compared to the fixed‐base frames. Conversely, the maximum roof displacements of the fixed and rocking frames are about the same. It is also noted that the effect of the vertical impact on the column associated with touchdown of the base plate is small because the difference in tensile and compressive forces is primarily due to the self‐limiting tensile force in the column caused by yielding of the base plate. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

⁴⁰Ar/³⁹Ar ages of blueschist facies pelitic schists from Qingshuigou in the Northern Qilian Mountains, western China     

Yong-Jiang  Liu  Franz  Neubauer  Johann  Genser  Akira  Takasu  Xiao-Hong  Ge Robert  Handler 《Island Arc》2006,15(1):187-198

Abstract   Pelitic schists from Qingshuigou in the Northern Qilian Mountains of China contain mainly glaucophane, garnet, white mica, clinozoisite, chlorite and piemontite. Isotopic age dating of these schists provides new constraints on the formation of the high-grade blueschists at Qingshuigou. White mica ⁴⁰Ar/³⁹Ar ages range from 442.1 to 447.5 Ma (total fusion age of single grain) and from 445.7 to 453.9 Ma (integrated age of white mica concentrates). These ages (442.1–453.9 Ma) represent the peak metamorphic ages or cooling ages of the blueschists during exhumation shortly after peak metamorphism. The ⁴⁰Ar/³⁹Ar dates in the present study are similar to ages previously reported for eclogites and blueschists in the area; this suggests that both the eclogites and pelitic sediments underwent high-grade metamorphism during the same subduction event. From this chronological evidence and the presence of well-developed Silurian remnant-sea flysch and Devonian molasse, it is concluded that the Northern Qilian Ocean had closed by the end of the Ordovician, and rapid orogenic uplift followed in the Devonian.  相似文献   

Collision structure in the upper crust beneath the southwestern foot of the Hidaka Mountains, Hokkaido, Japan as derived from explosion seismic observations     

Takeo Moriya  Hiroshi Okada  Takeshi Matsushima  Shuzo Asano  Toshikatsu Yoshii  Akira Ikami   《Tectonophysics》1998,290(3-4):181-196

The P-wave velocity structure of the upper crust beneath a profile ranging from Niikappu to Samani in the southwestern foot of the Hidaka Mountains, Hokkaido, Japan was obtained through analysis of refraction and wide-angle reflection data. The mountains are characterized by high seismicity and a large gravity anomaly. The present profile crosses the source region of the 1982 Urakawa-oki earthquake (M_s 6.8). The length of the profile is 66 km striking northwest and southeast. Along the profile, 64 vertical geophones were set up and 5 shot points were chosen. For each shot, a 400–600 kg charge of dynamite was detonated. The studied area is composed of four major geological belts: Neogene sedimentary rocks, the Kamuikotan belt, the Yezo Group, and the Hidaka belt. The measurement line crosses these geological trend at an oblique angle. The structure obtained is characterized by remarkable velocity variations in the lateral direction and reflects the surface geological characteristics. A thin, high-velocity layer (HVL) was found between low-velocity materials in the central part of the profile, beneath the Kamuikotan Metamorphic Belt, at a depth ranging from 0.5 to 6 km, overthrusting toward the west on the low-velocity materials consisting of Neogene sedimentary rocks, and forming gentle folds. Outlines of the velocity structure of the Hidaka Mountains yielded by other studies have shown a large-scale overthrust structure associated with the collision of the Outer Kurile and the Outer Northern Honshu Arcs. The shallow velocity structure inferred by the present study showed a similar (although small scale) overthrust structure. The obtained structure shows that the composite tectonic force, comprising westward movement of the Outer Kurile Arc and northward movement of the Outer Northern Honshu Arc, plays an important role in the evolution of the tectonic features of the crust and upper mantle in a wide depth range beneath the Hidaka Mountains.  相似文献   

Hydrogen Isotope Study of Fluid Inclusions in Vein Quartz of the Hishikari Gold Deposits, Japan   总被引：1，自引：0，他引：1  

Akira IMAI  Hidehiko SHIMAZAKI  Tomoko NISHIZAWA 《Resource Geology》1998,48(3):159-170

Abstract: The origin of mineralizing fluids responsible for the Hishikari vein-type epithermal Au deposits was studied on the basis of the hydrogen isotopic ratio (δD) of the inclusion fluid from vein quartz and adularia. The origin of hydrothermal fluids was estimated by combination of the present δ values and the oxygen isotopic ratios (δ¹⁸O) previously reported by Shikazono and Nagayama (1993). The water in the fluid inclusions was extracted by means of decrepitation of quartz at 500°C. Hydrogen was obtained by reduction of the collected water with Zn shot at 450°C. The δD values were determined by mass spectrometer. The δD values of inclusion fluid obtained from quartz range from –61 to –114%. These are significantly lower than the δD value of the thermal water presently venting from the Hishikari deposits and that of local meteoric water. Hydrogen isotopic fractionation between water and amorphous silica, which might have initially precipitated from the hydrothermal fluids at least partly, is not a probable cause of this isotopic depletion, while some water might have been released from the initial hydrous amorphous silica during recrystallization to quartz observed presently. Thus, a part of ore fluids for the Hishikari deposits is supposed to have been originated from the water having anomalous δD values of lower than –100%. Such D depletion cannot be caused by simple oxygen-shift of meteoric water or by contribution of magmatic volatiles. The δD values of water released from the shale samples of the Shimanto–Supergroup, a major host to the Hishikari veins range from –132 to –148%. Therefore, the anomalous δD values of inclusion fluids from some vein quartz and adularia suggest that the water released from hydrous minerals of the sedimentary basement rocks by dehydration or the groundwater isotopically exchanged with sedimentary rocks at elevated temperatures during circulation, partly contributed to the hydrothermal fluids responsible for the Hishikari deposits.  相似文献   

Crustal structure and accurate hypocenter determination along the Longmenshan fault zone     

赵珠  范军  郑斯华  长谷川昭  内茂木 《地震学报(英文版)》1997,10(6):761-768

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Crustal structure of the Mizuho Plateau, East Antarctica from geophysical data     

Kiyoshi Ito  Akira Ikami 《Journal of Geodynamics》1986,6(1-4)

Various kinds of geophysical surveys have been carried out in the Mizuho Plateau, East Antarctica by the Japanese Antarctic Research Expeditions (JARE). The correlation between the high-level gravity anomaly and the bedrock elevation is examined along a route where both data are sufficient to permit deriving a crustal model from gravity, radio-echo sounding and explosion seismic data. The bedrock elevation usually correlates well with the high-level gravity anomaly. However, along the traverse route S-H-Z from the Syowa to Mizuho stations, the bedrock elevation has a weak negative correlation with the high-level gravity anomaly. Such a weak negative correlation is attributed to the deeper part of the crust.The crustal structure between the Syowa and Mizuho stations is modeled from the gravimetric data and the radio-echo sounding of bedrock elevations, so as to fit the P-wave velocity structure derived from the data of explosion seismic experiments. Then the structure is extended from Syowa Station seaward across Lützow-Holm Bay and from Mizuho Station southeastwards inland, where only gravimetric data are available. Thus, a crustal section about 600 km long is obtained on a margin of East Antarctica. The depth of the Moho increases by about 7 km from Syowa Station to the point Y200 (71° 46′S, 48° 56′E), about 500 km from the coast. A graben-like structure is obtained along the line across Lützow-Holm Bay. This suggests that both sides of the bay are bounded by faults.  相似文献   

Effect of stirring on crystallization kinetics of basalt: texture and element partitioning     

Akira Kouchi  Akira Tsuchiyama  Ichiro Sunagawa 《Contributions to Mineralogy and Petrology》1986,93(4):429-438

Isothermal crystallization experiments on basalt have been carried out using an infrared heating furnace to investigate the effect of stirring. When stirring was not applied (static experiment), the results agreed well with previous experiments. But when stirring was applied and a flow of Reynolds number=10^–3–4 was present (dynamic experiment), considerably different results were obtained, especially in respect to the nucleation rate and the morphology of crystals. At T=25° C essentially similar results were obtained on the nucleation rates and morphologies of crystals in both static and dynamic experiments. However, at supercoolings larger than 45° C, nucleation density increased drastically in dynamic experiments reaching up to ten times as large as that in static experiments. Crystals of plagioclase and clinopyroxene were small and adapted acicular morphology regardless of T in dynamic experiments, and hyalopilitic textures were formed. A TTT-diagram shows that the nucleation incubation time is shorter in dynamic experiments than in static experiments. No compositional difference in major elements was found in plagioclase and clinopyroxene produced in both static and dynamic experiments. However, minor element concentrations, e.g., Mg in plagioclase and Ti, Al in clinopyroxene, were found to increase with both T and flow velocity. All these results imply that although chemical diffusion in the melts did not play an important role in the dynamic experiments, interface kinetics were important. It is suggested that hyalopilitic texture commonly seen in natural basalt is mainly due to flow in magma.  相似文献   

A model for mixing basaltic and dacitic magmas as deduced from experimental data     

Akira Kouchi  Ichiro Sunagawa 《Contributions to Mineralogy and Petrology》1985,89(1):17-23

It has been demonstrated experimentally that basaltic and dacitic magmas can be easily mixed to form both banded dacite and homogeneous andesite in less than a few hours. The presence of phenocrysts larger than 0.5 mm increased considerably the efficiency of mixing. Flow patterns in the experimental system were visualized using Pt spheres, which indicated that convection occurs in basalt melt, but not in dacite melt. The Reynolds numbers of the basaltic and dacitic melts in the experimental system were calculated to be about 10^–3 and 10^–6, respectively. Mixing proceeds initially by mechanical mixing of the two magmas in a large scale, but later by coupling interfacial convection and mutual diffusion. Thus, depending on the depth where vesiculation and following disruption of the magma occurs, banded pumice, homogeneous pumice and homogeneous andesite lava are erupted. The observed textures of mixed rocks of Plinian type eruption and the limiting occurrence of banded pumice are satisfactorily accounted for on this model.  相似文献   

Geophysical studies of crustal structure of the Ongul Islands and the Northern Mizuho Plateau, East Antarctica     

Akira Ikami  Kiyoshi Ito  Kazuo Shibuya  Katsutada Kaminuma 《Tectonophysics》1985,114(1-4)

Explosion seismic experiments, gravity measurements and aeromagnetic surveys were made in the northern Mizuho Plateau including the Ongul Islands, East Antarctica, from 1979 to 1982 by the Japanese Antarctic Research Expeditions. The objective of these field operations was to determine the crustal structure along the 300 km-long oversnow traverse route between Syowa and Mizuho Stations. Three big shots were fired; at sea near Syowa Station, in an ice hole near Mizuho Station and in an ice hole between both stations. Twenty-seven temporal seismic stations were set up along the route. Gravity measurements were carried out at 30 points along this route. Aeromagnetic surveys over the area were made four times.In the seismic experiments, clear refracted waves from the Conrad (estimated depth 30 km) and the Moho (estimated depth 40 km) discontinuities were recorded. No layer with a velocity of less than 6 km/s was found in the Ongul Islands nor beneath the ice sheet in the surveyed area. The P-wave velocity in the upper layer varies with depth from 6.0 km/s on the surface to 6.4 km/s at a depth of 13 km. Comparing the observed record section with synthetic seismograms, it was derived that the Conrad was not associated with a sharp velocity discontinuity, but a linear velocity increase of 0.55 km/s in a transition zone of 2.4 km thick. Velocities of P^* and P_n were determined as 6.95 km/s and 7.93 km/s assuming a flat layered structure.Bouguer gravity anomalies could not be calculated along the whole profile because of a lack of data on bedrock topography, so reduced gravity anomalies were calculated. These anomalies indicate no abrupt changes of the bedrock topography.  相似文献   

Oblique and near collision subduction, Sagami and Suruga Troughs —preliminary results of the French-Japanese 1984 Kaiko cruise, Leg 2     

Kazuaki Nakamura  Vincent Renard  Jacques Angelier  Jacques Azema  Jacques Bourgois  Christine Deplus  Kantaro Fujioka  Yozo Hamano  Philippe Huchon  Hajimu Kinoshita  Pierre Labaume  Yujiro Ogawa  Tetsuzo Seno  Akira Takeuchi  Manabu Tanahashi  Akinori Uchiyama  Jean-Louis Vigneresse 《Earth and Planetary Science Letters》1987,83(1-4)

Leg 2 of the French-Japanese 1984 Kaiko cruise has surveyed the Suruga and the Sagami Troughs, which lie on both sides of the northwestward moving and colliding Izu-Bonin Ridge, the northernmost part of the Philippine Sea plate. The transition from the Nankai Trough to the Suruga Trough is characterized by northward decrease in width of the accretionary prism, in good agreement with the increasing obliquity between the through axis and the direction of the convergence, as the strike of the convergent boundary changes from ENE-NNE to south-north. South of the area, the southern margin of the Zenisu Ridge shows contractional deformations. This supports the interpretation made by the team of Leg 1 who studied the western extension of the area we studied, that it is an intra-oceanic thrusting of the ridge over the Shikoku Basin. In the Sagami Trough, where the relative motion is highly oblique to the plate boundary, active subduction is mostly confined in the east-west trending portions of the trough located south of the Boso Peninsula and along the lower Boso Canyon, near the TTT triple junction. In between, the present motion is mainly right-lateral along the northwest trending Boso escarpment. However, an inactive but recent (Pliocene to lower Pleistocene) accretionary prism exists south of the Boso escarpment, which suggests that the relative motion was more northerly than at present before about 1 Ma ago.  相似文献