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81.
Changes in magnetic and fractal properties of fractured granites near the Nojima Fault, Japan 总被引:2,自引:0,他引:2
Abstract Anisotropy of magnetic susceptibility (AMS) has been used to infer finite strain fabrics in plastically deformed rocks, but there are few studies of magnetic properties in fractured fault rocks. Changes in magnetic and fractal properties of fractured granites from the Disaster Prevention Research Institute, Kyoto University (DPRI) 500 m drilling core towards the Nojima Fault and of the well-foliated fault gouge are described. Fractal analysis of fractured granites shows that the fractal dimension ( D ) increases linearly toward the gouge zone of the fault. In weakly fractured granites ( D = 1.05–1.24), it was found that the degree of AMS correlates positively with the fractal dimension, suggesting a fracture-related magnetic fabric due to fracturing. In strongly fractured granites ( D = 1.25–1.50), weaker, nearly isotropic AMS is found, suggesting erasure by the fragmentation of the magnetic minerals. Within the fault gouge zone, an isotropic AMS fabric was found, as well as twofold increases in magnetic intensity and susceptibility. These changes reflect the production of new magnetite grains, subsequently confirmed by hysteresis studies, which suggests that fault gouge might be regarded as the source of the regional geomagnetic field contrast along active faults. Thus, AMS is clearly a potentially useful tool for inferring the fracturing texture of magnetic minerals in fractured rocks and detecting active faults from the high susceptibility contrast of fault gouge. 相似文献
82.
The theory of physical interaction field by a differential geometrical approach combines the deformation field with the physical field (e.g., electromagnetic field), and derives a new tensorial relation between the deformation and the dielectric anisotropy of the crustal rocks. This relation can be applied to dielectric anisotropies of deformed natural rocks such as mylonites or gneisses. The dielectric anisotropies of mylonites are observed to increase as plastic strains of mylonites increase. Moreover, the derived tensorial relation can be linked to the electromagnetic potential field (deformational anomalies) in a deformed crust. A physico-geometrical consideration on this theory of physical interaction field is mathematically similar to ones on the theory of field in the Finsler space or on the concept of a unified gauge field. 相似文献
83.
Hiroshi Tsuno Atsuyuki Ohta Hiroyuki Kagi Noboru Imai Hiroaki Tao Masaharu Nomura 《Geostandards and Geoanalytical Research》2006,30(1):55-62
The oxidation states of chromium in GSJ JSO-2 (artificially contaminated soil) and three other geochemical reference materials (GSJ JSO-1, JLS-1 and JMS-1) were observed using X-ray near edge structure (XANES). For comparison, other artificially contaminated soil materials (mimic-JSO-2) were prepared by adding Cr(VI) into JSO-1. Their oxidation states of chromium were determined using XANES. The chromium contents were 1118 μg g-1 for JSO-2, 1352 μg g-1 for mimic-JSO-2 and 69-113 μg g-1 for the other reference materials. Most chromium was present as hexavalent in mimic-JSO-2. No hexavalent species were detected in other samples. These results for chromium oxidation state in JSO-2 and mimic-JSO-2 obtained with XANES resembled those obtained from a chemical extraction method. The present JSO-2 has no trace of Cr(VI), although Cr(VI) was added as a major species during preparation. On the other hand, the content of Cr(VI) obtained in mimic-JSO-2 agreed with the original Cr(VI) content. A time-elapse study showed that Cr(VI) contents in mimic-JSO-2 decreased gradually to 70% of the original abundance during 240-day preservation in dry conditions. Moreover, the abundance of Cr(VI) decreased markedly to 15% after 240 days in the wet mimic-JSO-2 containing 20% m/m of water. These experiments suggested that soil humidity enhanced the reduction of Cr(VI) and that Cr(VI) was reduced even in dry conditions. Consequently, it is reasonable to infer that Cr(VI) doped into JSO-2 was completely reduced to Cr(III) during the preservation period of 5 years. The certification of the long-term stability of the chemical form in reference materials will be much more important in future. 相似文献
84.
Abstract Middle Miocene to Quaternary primitive basalts and high magnesian andesite (HMA) in North Hokkaido resulted from three periods of intense volcanism; early-stage (12–10 Ma), middle-stage (9–7 Ma) and late-stage (3–0 Ma). Based on the chemical compositions of olivines and chromian spinels and bulk chemistry of the primitive rocks, we examined depths of segregation of the calculated primary magmas and the degrees of partial melting of the source mantle. In the context of asthenospheric mantle upwelling, petrological data from the present study can be accounted for by the secular change in the depth of magma segregation from the upwelled asthenospheric mantle, which is composed of fertile peridotite. Thus, the early-stage primary magmas were generated by higher degrees of partial melting of the shallower part of hot asthenospheric mantle, whereas the middle- and late-stage primary magmas resulted from lower degrees of partial melting of a deeper part of the asthenospheric mantle. The early-stage HMA magma was generated by partial melting of the remnant subcontinental lithospheric mantle composed of refractory peridotite. This melting might have resulted from an increased geothermal gradient caused by upwelling of hot asthenosphere. 相似文献
85.
Abstract The Sagara oil field is located in the Neogene Kakegawa Basin, close to the Izu collision zone at the junction between the main Japanese Islands and the Izu–Bonin Arc. The Sagara oil field is one of the few oil fields situated in a forearc basin on the Pacific side of Japan and is present in a sedimentary basin with poor oil-generating potential. Several crude oils from Sagara oil field were investigated to infer their origin. Organic geochemical characteristics of Sagara oils showed the influences of light biodegradation, migration-contamination, and migration-fractionation. The maturity levels of Sagara oils evaluated based on abundant alkylnaphthalenes corresponded to 0.9–1.2% vitrinite reflectance. Sagara oils were characterized by significant amounts of higher plant biomarkers, a high pristane/phytane ratio and an absence of organic sulphur compounds, suggesting a siliciclastic source rock deposited under nearshore to fluvial–deltaic environments. Numerous faults and fractures in the active forearc basin provided excellent conduits and facilitated upward migration of light hydrocarbons generated at greater depth in the Kakegawa Basin. 相似文献
86.
Short-range prediction experiments of the Kuroshio path variabilities south of Japan 总被引:1,自引:0,他引:1
Assimilation and prediction experiments of the Kuroshio path variability south of Japan were conducted to investigate the
predictability of the Kuroshio path. The assimilation and prediction system is composed of an eddy-resolving model and a three-dimensional
variational analysis scheme with vertical coupled temperature–salinity empirical orthogonal function modes. The sea surface
height (SSH) variability and the variations of the Kuroshio path of the assimilation fields are in good agreement with those
observed. The results of the assimilation are then used as the initial conditions for 138 cases of 90-day prediction experiments
conducted from 1993 to 2004. The predictive limit of our system is assessed by the SSH anomaly in the assimilation field and
is found to be around 40–60 days, which is much longer than that of the persistence. The prediction results show good performance
in the transition stage from a straight to a meandering path. For example, a large meandering event that occurred in August
2004 is successfully predicted in a 2-month forecast. Two types of failure cases are investigated. One is a case where the
eastward propagation speed of the meander is faster than a real state. The dynamical response of the model to the assimilation
revealed that an initial shock, caused by the dynamically unbalanced initial condition, induces the fast eastward propagation
of the meander. The other case exhibits an unrealistic meander. In this case, a cold anomaly at an intermediate layer in the
initial condition grows rapidly and results in the unrealistic meander. This implies that the Kuroshio path south of Japan
has a chaotic nature. These facts revealed by the failure cases give us some insight for improving the predictive skill of
the Kuroshio path variability. 相似文献
87.
Journal of Oceanology and Limnology - 相似文献
88.
Shusaku Inoue Anil C. Wijeyewickrema Hiroyuki Matsumoto Hiroyuki Miura Priyantha Gunaratna Manoj Madurapperuma Toru Sekiguchi 《Pure and Applied Geophysics》2007,164(2-3):395-411
The December 26, 2004 Sumatra-Andaman earthquake that registered a moment magnitude (Mw) of 9.1 was one of the largest earthquakes in the world since 1900. The devastating tsunami that resulted from this earthquake
caused more casualties than any previously reported tsunami. The number of fatalities and missing persons in the most seriously
affected countries were Indonesia - 167,736, Sri Lanka - 35,322, India - 18,045 and Thailand - 8,212. This paper describes
two field visits to assess tsunami effects in Sri Lanka by a combined team of Japanese and Sri Lankan researchers. The first
field visit from December 30, 2004 – January 04, 2005 covered the western and southern coasts of Sri Lanka including the cities
of Moratuwa, Beruwala, Bentota, Pereliya, Hikkaduwa, Galle, Talpe, Matara, Tangalla and Hambantota. The objectives of the
first field visit were to investigate the damage caused by the tsunami and to obtain eyewitness information about wave arrival
times. The second field visit from March 10–18, 2005 covered the eastern and southern coasts of Sri Lanka and included Trincomalee,
Batticaloa, Arugam Bay, Yala National Park and Kirinda. The objectives of the second visit were mainly to obtain eyewitness
information about wave arrival times and inundation data, and to take relevant measurements using GPS instruments. 相似文献
89.
J. Ignacio Martínez Yusuke Yokoyama Andres Gomez Adriana Delgado Hiroyuki Matsuzaki Esteban Rendon 《Journal of South American Earth Sciences》2010,29(2):214-224
The detailed stratigraphic survey and paleontological study (mollusks, corals, foraminifera and ostracods) of four low-level, ~3 m, marine terrace sections: Punta Canoas, Manzanillo del Mar, Playa de Oro, and Tierra Bomba Island, from the Cartagena region, southern Caribbean, supplemented with 22 radiocarbon dates, reveals that the northern terraces were deposited as parasequences in a clastic depositional system compared to the Tierra Bomba Island succession that was deposited in a carbonate depositional system between ~3600 and ~1700 cal yrs BP. Drier conditions and the southern location of the ITCZ at about 3 ka triggered stronger easterly Trades and more dynamic southwestward sediment drift fed by the Magdalena River mouth, thus promoting the formation of sand spits that ultimately isolated the Cienaga de Tesca coastal lagoon from the Caribbean Sea. Our estimates support the hypothesis that the present position of the terraces is the product of neotectonism rather than a higher 3 ka, sea-level. Upheaval of the terraces varies between ~3.8 mmyr?1 at Punta Canoas and ~2.2 mmyr?1 at Tierra Bomba to ~1.5 mmyr?1 at Manzanillo del Mar and Playa de Oro terraces. Our study corroborates previous contentions on the role of mud diapirism and the dynamics of the Dique Fault as late Holocene upheaval mechanisms. 相似文献
90.
Most climate models project a weakening of the Walker circulation under global warming scenarios. It is argued, based on a global averaged moisture budget, that this weakening can be attributed to a slower rate of rainfall increase compared to that of moisture increase, which leads to a decrease in ascending motion. Through an idealized aqua-planet simulation in which a zonal wavenumber-1 SST distribution is prescribed along the equator, we find that the Walker circulation is strengthened under a uniform 2-K SST warming, even though the global mean rainfall–moisture relationship remains the same. Further diagnosis shows that the ascending branch of the Walker cell is enhanced in the upper troposphere but weakened in the lower troposphere. As a result, a "double-cell" circulation change pattern with a clockwise(anti-clockwise) circulation anomaly in the upper(lower) troposphere forms, and the upper tropospheric circulation change dominates. The mechanism for the formation of the "double cell" circulation pattern is attributed to a larger(smaller) rate of increase of diabatic heating than static stability in the upper(lower) troposphere. The result indicates that the future change of the Walker circulation cannot simply be interpreted based on a global mean moisture budget argument. 相似文献