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1.
Abstract This paper provides untilted paleomagnetic data obtained from the early Miocene strata around the Kanazawa‐Iozen area, in the eastern part of south‐west Japan. A thick pile of volcaniclastics and marine transgressive sediments underlie the area; they were deposited in the early stage of the Japan Sea opening event. Progressive thermal demagnetization tests isolated stable primary magnetic vectors from eight sites in the upper part of the Iozen Formation. Overall, the tilt‐corrected mean direction of this unit is D = 36.4°, I = 51.6° and α95 = 12.1. Together with a published paleomagnetic and chronological database, the present results suggest that clockwise rotation of south‐west Japan, linked to the back‐arc opening, commenced in the early Miocene and accelerated at the same time as rapid subsidence along the Japan Sea coast. Post‐opening, differential rotation within the eastern part of south‐west Japan is assumed, based on selected paleomagnetic data from the latest Early Miocene. 相似文献
2.
Ken Goto Takahiro Itoh Takahiko Nagayama Rei Utsunomiya Daizo Tsutsumi Takahisa Mizuyama 《山地科学学报》2016,13(2):369-376
Bedload governs riverbed channel variations and morphology, it is necessary to determine bedload discharge through an arbitrary cross section in a mountain river. A new system with submerged load cells has been developed to directly measure bedload discharge. The system consists of: (1) an iron box which is 1 m long, 0.5 m wide and 0.1 m in depth, (2) two submerged load cells 0.7 m apart, (3) a pressure sensor and, (4) an electromagnetic velocity meter. This system has been designed to exclude the effect of the hydraulic pressure of water on direct measurements of bedload particle weight. Initial tests in a laboratory were conducted to examine the accuracy of measurements with the system under aerial conditions. The system has been installed in the supercritical flume in Ashi-arai-dani River of the Hodaka Sedimentation Observatory of the Disaster Prevention Research Institute (DPRI) of Kyoto University to obtain bedload discharge under natural conditions. Flume tests were conducted in this channel by artificial supply of uniform sediment particles of several grain sizes. The average velocity of the sediment particles near the bed was estimated using cross-correlation functions for weight waves obtained by the two load cells. Bedload discharge calculations were based on time integration of the product of sediment velocity and sediment weight obtained by the two load cells. This study clarifies the reasons why bedload measurements are difficult, and provides some solutions using the monitoring systems with submerged load cells through the field measurements. Additionally, the applicability of bedload measurement with the submerged load cells is explained based on experimental artificial sediment supply data. 相似文献
3.
Maki Morimoto Kyoko Kawanobe Osamu Abe Takayoshi Kawai Toshiyuki Kawamura Kunio Shirasawa 《水文研究》2010,24(7):904-916
In winter, lakes and lagoons at high altitudes or high latitudes have interesting hydrological cycles that differ from those in other seasons or in other regions, because water surfaces are covered with ice. Hydrological balances of lakes and lagoons are complex dynamic systems, and to elucidate them, isotopic tracers of water have been used as effective tools along with observations of precipitation, evaporation, inflows, and outflows. Here, to understand hydrological processes during freezing periods in the brackish Saroma‐ko Lagoon, Hokkaido, northern Japan, we examined horizontal and vertical distributions of salinity and isotope compositions of lagoon water and ice in 2005 and 2006. Horizontal and vertical gradients of salinity and isotope compositions were observed from the river mouth to the sea channel, and factors determining these distributions were considered. The mixing of freshwater and seawater and a freezing effect were presumed to be factors in relationships between salinity and isotopes and in relationships between surface waters and ice just above the water. A simple box model for water balance was constructed based on these putative factors to reproduce the distributions of salinity and isotope compositions of surface waters and ice. An evaluation of the model revealed that this hydrological system is controlled primarily by horizontal advection of the epilimnion, freshwater influx, and the ice growth rate. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
4.
Masao Ohno Tsutomu Sato Kenji Notsu Hiroshi Wakita Kunio Ozawa 《Pure and Applied Geophysics》2006,163(4):647-655
Anomalous water level changes were observed at two wells associated with seismic swarm activity off Izu Peninsula on March,
1997. These are coseismic water level drops followed by gradual postseismic water level rise at the time of large earthquakes
during the swarm activity. The post-seismic water level rises, which can be fitted by an exponential function with a time
constant of about six hours, are explained in terms of the horizontal pressure diffusion due to the pressure gradient in the
aquifer induced by the coseismic static strain. 相似文献
5.
6.
Strain and tilt changes measured during a water injection experiment at the Nojima Fault zone, Japan 总被引:2,自引:0,他引:2
Kunio Fujimori Hiroshi Ishii Atsushi Mukai Shigeru Nakao Shigeo Matsumoto Yasuhiro Hirata 《Island Arc》2001,10(3-4):228-234
Abstract In order to make geophysical and geological investigations of the Nojima Fault on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic source faults of the 1995 Hyogo-ken Nanbu earthquake of M 7.2. A new multicomponent borehole instrument was installed at the bottom of the 800 m borehole and continuous observations of crustal strain and tilt have been made using this instrument since May 1996. A high-pressure water injection experiment within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water injection, contraction of approximately 0.7 × 10−7 str (almost parallel to the fault) and tilt of approximately 1 × 10-7 rad in the sense of upheaval toward the injection site were observed. In addition to these controlled experiments, the strainmeter and tiltmeter also recorded daily variations. We interpret strain and tilt changes to be related to groundwater discharge and increased ultra-micro seismicity induced by the injected water. 相似文献
7.
Yoshimi Kawai Hiroshi Kawamura Sumio Tanba Kentaro Ando Kunio Yoneyama Norio Nagahama 《Journal of Oceanography》2006,62(6):825-838
In order to investigate the validity of buoy-observed sea surface temperature (SST), we installed special instruments to measure
near-surface ocean temperature on the TRITON buoy moored at 2.07°N, 138.06°E from 2 to 13 March 2004, in addition to a standard
buoy sensor for the regular SST measurement at 1.5-m depth. Large diurnal SST variations were observed during this period,
and the variations of the temperatures at about 0.3-m depth could be approximately simulated by a one-dimensional numerical
model. However, there was a notable discrepancy between the buoy-observed 1.5-m-depth SST (SST1.5m) and the corresponding model-simulated temperature only during the daytime when the diurnal rise was large. The evaluation
of the heat balance in the sea surface layer showed that the diurnal rise of the SST1.5m in these cases could not be accounted for by solar heating alone. We examined the depth of the SST1.5m sensor and the near-surface temperature observed from a ship near the buoy, and came to the conclusion that the solar heating
of the buoy hull and/or a disturbance in the temperature field around the buoy hull would contribute to the excessive diurnal
rise of the SST1.5m observed with the TRITON buoy. However, the temperature around the hull was not sufficiently homogenized, as suggested in
a previous paper. For the diurnal rise of the SST1.5m exceeding 0.5 K, the daytime buoy data became doubtful, through dynamics that remain to be clarified. A simple formula is
proposed to correct the unexpected diurnal amplitude of the buoy SST1.5m. 相似文献
8.
Tadao Nishiyama Hibiki Eguchi Dai Shiosaki Akira Yoshiasa Nobutatsu Mochizuki Yasushi Mori Kazumasa Sugiyama Hiroshi Arima Kunio Yubuta 《Island Arc》2021,30(1):e12382
Spinifex-like textured metaperidotites from the Higo Metamorphic Rocks (HMR), west-central Kyushu, Japan, may be formed by high-pressure dehydration of antigorite, and may indicate deep subduction of serpentinite reaching a pressure–temperature condition of 1.6 GPa and 740–750 °C. Three rock types have been identified based on mineral assemblage and rock texture: Type I (L) consisting of medium-grained (1–5 cm long) olivine + enstatite + chromite ±tremolite with secondary talc and anthophyllite that occurs in low-grade metamorphic rocks of the biotite zone, Type I (H) of coarse-grained (up to 10 cm long) olivine + enstatite (with clinoenstatite lamella) + chromite ±tremolite with secondary talc that occurs in high-grade metamorphic rocks of the garnet-cordierite zone, and Type II composed of Al-spinel + chlorite + olivine + apatite + ilmenite with minor sodic gedrite in the garnet-cordierite zone together with Type I (H). Olivines in all rock types are mostly serpentinized during exhumation. The chromite-olivine thermometer gives 560–690 °C for Type I (L) rocks, and the spinel-olivine thermometer gives 610–740 °C for Type II rocks. The peak metamorphic pressure will be higher than 1.6 GPa based on the location of the experimentally determined invariant point (P = 1.6 GPa and T = 670 °C) of antigorite + forsterite + enstatite + talc + H2O. This estimate is consistent with the occurrence of chlorite in Type II rocks, which is stable up to 890 °C at 2.0 GPa. The spinifex-like textured metaperidotites occur as small bodies in the low P/T type gneisses, implying tectonic juxtaposition of them probably during exhumation of the HMR. Recent findings of medium pressure (0.9–1.2 GPa) granulites and gneisses from the HMR may indicate that the HMR has a deep root into the wedge mantle from which the spinifex-like textured metaperidotites have derived. 相似文献
9.
Alexander N. Krot Michail I. Petaev Shoichi Itoh Timothy J. Fagan Hisayoshi Yurimoto Michael K. Weisberg Matsumi Komatsu Klaus Keil 《Chemie der Erde / Geochemistry》2004,64(3):185-239
Amoeboid olivine aggregates (AOAs) are the most common type of refractory inclusions in CM, CR, CH, CV, CO, and ungrouped carbonaceous chondrites Acfer 094 and Adelaide; only one AOA was found in the CBb chondrite Hammadah al Hamra 237 and none were observed in the CBa chondrites Bencubbin, Gujba, and Weatherford. In primitive (unaltered and unmetamorphosed) carbonaceous chondrites, AOAs consist of forsterite (Fa<2), Fe, Ni-metal (5-12 wt% Ni), and Ca, Al-rich inclusions (CAIs) composed of Al-diopside, spinel, anorthite, and very rare melilite. Melilite is typically replaced by a fine-grained mixture of spinel, Al-diopside, and ±anorthite; spinel is replaced by anorthite. About 10% of AOAs contain low-Ca pyroxene replacing forsterite. Forsterite and spinel are always 16O-rich (δ17,18O∼−40‰ to −50‰), whereas melilite, anorthite, and diopside could be either similarly 16O-rich or 16O-depleted to varying degrees; the latter is common in AOAs from altered and metamorphosed carbonaceous chondrites such as some CVs and COs. Low-Ca pyroxene is either 16O-rich (δ17,18O∼−40‰) or 16O-poor (δ17,18O∼0‰). Most AOAs in CV chondrites have unfractionated (∼2-10×CI) rare-earth element patterns. AOAs have similar textures, mineralogy and oxygen isotopic compositions to those of forsterite-rich accretionary rims surrounding different types of CAIs (compact and fluffy Type A, Type B, and fine-grained, spinel-rich) in CV and CR chondrites. AOAs in primitive carbonaceous chondrites show no evidence for alteration and thermal metamorphism. Secondary minerals in AOAs from CR, CM, and CO, and CV chondrites are similar to those in chondrules, CAIs, and matrices of their host meteorites and include phyllosilicates, magnetite, carbonates, nepheline, sodalite, grossular, wollastonite, hedenbergite, andradite, and ferrous olivine.Our observations and a thermodynamic analysis suggest that AOAs and forsterite-rich accretionary rims formed in 16O-rich gaseous reservoirs, probably in the CAI-forming region(s), as aggregates of solar nebular condensates originally composed of forsterite, Fe, Ni-metal, and CAIs. Some of the CAIs were melted prior to aggregation into AOAs and experienced formation of Wark-Lovering rims. Before and possibly after the aggregation, melilite and spinel in CAIs reacted with SiO and Mg of the solar nebula gas enriched in 16O to form Al-diopside and anorthite. Forsterite in some AOAs reacted with 16O-enriched SiO gas to form low-Ca pyroxene. Some other AOAs were either reheated in 16O-poor gaseous reservoirs or coated by 16O-depleted pyroxene-rich dust and melted to varying degrees, possibly during chondrule formation. The most extensively melted AOAs experienced oxygen isotope exchange with 16O-poor nebular gas and may have been transformed into magnesian (Type I) chondrules. Secondary mineralization and at least some of the oxygen isotope exchange in AOAs from altered and metamorphosed chondrites must have resulted from alteration in the presence of aqueous solutions after aggregation and lithification of the chondrite parent asteroids. 相似文献
10.