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1.
Non-volcanic deep low-frequency tremors accompanying slow slips in the southwest Japan subduction zone 总被引:5,自引:1,他引:5
Non-volcanic deep low-frequency tremors in southwest Japan exhibit a strong temporal and spatial correlation with slow slip detected by the dense seismic network. The tremor signal is characterized by a low-frequency vibration with a predominant frequency of 0.5–5 Hz without distinct P- or S-wave onset. The tremors are located using the coherent pattern of envelopes over many stations, and are estimated to occur near the transition zone on the plate boundary on the forearc side along the strike of the descending Philippine Sea plate. The belt-like distribution of tremors consists of many clusters. In western Shikoku, the major tremor activity has a recurrence interval of approximately six months, with each episode lasting over a week. The tremor source area migrates during each episode along the strike of the subducting plate with a migration velocity of about 10 km/day. Slow slip events occur contemporaneously with this tremor activity, with a coincident estimated source area that also migrates during each episode. The coupling of tremor and slow slip in western Shikoku is very similar to the episodic tremor and slip phenomenon reported for the Cascadia margin in northwest North America. The duration and recurrence interval of these episodes varies between tremor clusters even on the same subduction zone, attributable to regional difference in the frictional properties of the plate interface. 相似文献
2.
Yuri D. Zakharov Yasunari Shiget Kazushige Tanabe Yasuhiro I Olga P. Smyshlyaev Ekaterina A. Sokolov Alexer M. Popov Tatiana A. Velivetskay Tamara B. Afanasyeva 《《地质学报》英文版》2007,81(6):1049-1069
Paleoclimatic settings have been reconstructed for the Campanian using original oxygen-isotopic analyses of well-preserved molluskan and foraminifera shells from Russian Far East, Hokkaido, USA, Belgium and some DSDP holes (95, 98, 102, 390A, and 392A) in North Atlantic. Early Early Campanian climatic optimum has been recognized from data on high bottom shelf water paleotemperatures in middle latitudes of both the western circum-Pacific (to 24.2°C) and the eastern circum-Pacific (to 26.4°C) areas and high bottom shallow water paleotemperatures in high latitudes of the Koryak Upland (22.4–25.5°C), which agrees with the data on the Campanian Barykovskaya flora in high latitudes (Golovneva and Herman, 1998) and Jonker flora and its equivalents in middle latitudes. Judging from the data on comparatively high bottom shallow water paleotemperature values in high latitudes, South Alaska (19.4°C) and the Koryak Upland (22.4–25.5°C), we also expect Latest Campanian temperature maximum, which has not been confirmed, however, for low and middle latitudes by neither of isotopic nor paleobotanic data now. Main climatic tendency during the Campanian (with the exception of Latest Campanian) has been learned from isotopic composition of Campanian aragonitic ammonoid shells from the Hokkaido-South Sakhalin (Krilyon) marine basin. In contrary to Huber’s et al. (2002) assumption, we expect warm greenhouse conditions during the most part of the Campanian. 相似文献
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4.
Transmission electron microscopy of a hydrated interplanetary dust particle indicates that it consists largely of a poorly crystalline phyllosilicate containing Fe, Mg and Al with an interlayer spacing of 10 to 12Åand so is distinct from the major phyllosilicate in CI and CM carbonaceous chondrites. The silicate is probably an Fe- and Mg-rich smectite or mica. Submicron, spherical to euhedral pyrrhotite and pentlandite are prominent. Unusual, low-Ni ( < 3 at.% Ni) pentlandite is also common and typically occurs as rectangular platelets. Unlike many chondritic interplanetary dust particles, olivine is rare and pyroxene was not observed. Other less abundant phases are magnetite, chromite, and an unidentified phase containing Fe, Mg, Si, Ca, and Mn. This particle differs from a hydrated micrometeorite described previously by Brownlee [1], indicating there are mineralogically different subsets of hydrated interplanetary dust particles. Despite gross similarities in mineralogy between the particle and the carbonaceous chondrites, they show appreciable differences in detail. 相似文献
5.
This paper presents the development and utilisation of an automated image processing algorithm for detection and analysis
of grains. Using optical polarising microscopy, a set of colored images are collected from an area on a thin section. A filtering
operation, using rotation of a morphological alternating sequence filter (based on a structuring element), is used to remove
twinning features within individual grains. Filtering is followed by the watershed segmentation technique to determine grain
boundaries. The method is used for the identification of calcite grains in marble and the subsequent analysis of morphological
anisotropy. 相似文献
6.
Estimation of elastoplastic deformation around an underground opening induced by the excavation of it, especially displacement and strain field in plastic region, is presented in this paper, as well as the formulation for calculating the displacement and strain in the plastic region around the underground opening by the coupled Boundary Element Method - Characteristics Method (BEM-CM). In this method, the non-associated flow rule is adopted to calculate the displacement and strain field in the plastic region, which is determined by the integration of the displacement along characteristics lines under the boundary condition of the elastic displacement on an elastoplastic interface analysed. It is shown that this method is one of the accurate and effective methods for estimating not only the shape and extent of the plastic region but also the state of the displacement and strain in the plastic region around the underground opening, comparing the theoretical solution with numerical results by this method for a circular opening under hydrostatic initial stress condition. Furthermore, this method is applied to rectangular and horse-shoe shaped openings and the characteristics of the strain field in the plastic region are discussed. © 1997 by John Wiley & Sons, Ltd. 相似文献
7.
Abstract— Enstatite is one of the major constituent minerals in carbonaceous chondrites. Hydrothermal alteration experiments (26 in total) of enstatite were carried out at pH 0, 6, 7, 12, 13, and 14, at temperatures of 100, 200, and 300 °C, and for run durations of 24, 72, 168, and 336 h in order to provide constraints on the aqueous‐alteration conditions of the meteorites. The recovered samples were studied in detail by using powder X‐ray diffraction, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Under acidic and mildly acidic conditions (pH 0, 6), no significant alteration occurred, whereas under neutral to alkaline conditions (pH 7–14), serpentine and saponite formed in various proportions by replacing enstatite. At 300 °C for 168 h, serpentine formed under neutral to moderately alkaline conditions (pH 7, 12), and serpentine and saponite formed as unit cell‐scale coherent intergrowths under highly alkaline conditions (pH 13, 14). The amounts of phyllosilicates have a tendency to increase with increasing pH, temperature, and run duration. There is also a tendency for saponite to form at higher pH and temperature and under longer run‐durations than serpentine. The results indicate that alteration of enstatite is strongly dependent on the experimental conditions, especially pH. They suggest that CM chondrites experienced aqueous alteration under neutral to alkaline conditions, whereas CV and CI chondrites experienced aqueous alteration under more alkaline conditions. The results also suggest that aqueous alteration in CI chondrites occurred at higher temperatures than in CM chondrites, and aqueous alteration in CV chondrites occurred at even higher temperatures than in CI chondrites. 相似文献
8.
Kazushige Tomeoka 《Geochimica et cosmochimica acta》2010,74(15):4438-6079
A petrographic and electron microscopic study of the Mokoia CV3 carbonaceous chondrite shows that all of the chondrules and inclusions (>400 μm in diameter) and most of their fine-grained rims studied (referred to as chondrules/rims) contain various amounts of hydrous phyllosilicates (mostly saponite) formed by aqueous alteration of anhydrous silicates. The rims mainly consist of fine-grained olivine and saponite in varying proportions and contain crosscutting veins of Fe-rich olivine. The boundaries between the chondrules and their rims are irregular and show abundant evidence of aqueous alteration interactions between them. In contrast, the host matrix contains very minor amounts of saponite and shows no evidence of such extensive aqueous alteration. The boundaries between the chondrules/rims and the matrix are sharp and show no traces of the matrix having been involved in the alteration of the chondrules/rims. These observations indicate that the aqueous alteration in the chondrules/rims did not occur in the present setting.We suggest that the chondrules/rims are actually clasts transported from a location on the meteorite parent body different from where the Mokoia meteorite was from. The aqueous alteration of the chondrules/rims probably occurred there. The veins in the rims were originally fractures produced in an interchondrule matrix by impacts; these were later filled by Fe-rich olivine during aqueous activity. This location was then involved in impact brecciation, and individual chondrules were ejected as clasts with remnants of the matrix surrounding them. During the continuing brecciation, those chondrule/rim clasts were transported, mixed with anhydrous matrix grains, and finally lithified to the present meteorite. Therefore, the rims are fragmented remnants of a former matrix.Textures characterized by fine-grained rims surrounding chondrules in chondrites have been widely thought to have formed in the solar nebula before they accreted into their parent bodies. However, our results suggest that some textures may not be explained by such an accretionary model; instead, the multi-stage parent-body process modeled for the Mokoia rim formation may be a more plausible explanation. 相似文献
9.
B. Obara 《Mineralogy and Petrology》2007,91(3-4):271-285
Summary The present paper is concerned with the development and application of an effective automatic algorithm of image analysis
in order to detect grain boundaries on microscope images of Redziny dolostone and Wisniowka quartzite. The algorithm utilises
sets of 6 colour images for each measurement field on thin sections, which are recorded using an optical polarizing microscope
in different polarization set-ups.
The proposed method is based on an image pre-processing procedure that is focused on colour system transformation, followed
by rock grain boundaries segmentation using the image analysis methods for each colour image. For the image pre-processing
procedure, several colour system transformations were selected and compared. By using the alternative colour systems that
concentrate on colour information we are able to minimise the effects of internal micro-structures in the grain boundaries
segmentation procedure. The grain boundary maps obtained confirm that the use of an approximately perceptually uniform colour
system as an image pre-processing procedure can significantly improve the rock grain segmentation. This newly-developed method
may facilitate petrographical and stereological studies of rock structures. 相似文献
10.
Naotaka TOMIOKA Kazushige TOMEOKA Keiko NAKAMURA‐MESSENGER Toshimori SEKINE 《Meteoritics & planetary science》2007,42(1):19-30
Abstract— Micrometeorites have been significantly altered or melted by heating, which has been mainly ascribed to aerodynamic drag during atmospheric entry. However, if a major fraction of micrometeorites are produced by impacts on porous asteroids, they may have experienced shock heating before contact with the Earth's atmosphere (Tomeoka et al. 2003). A transmission electron microscope (TEM) study of the matrix of Murchison CM chondrite experimentally shocked at pressures of 10–49 GPa shows that its mineralogy and texture change dramatically, mainly due to shock heating, with the progressive shock pressures. Tochilinite is completely decomposed to an amorphous material at 10 GPa. Fe‐Mg serpentine is partially decomposed and decreases in amount with increasing pressure from 10 to 30 GPa and is completely decomposed at 36 GPa. At 49 GPa, the matrix is extensively melted and consists mostly of aggregates of equigranular grains of Fe‐rich olivine and less abundant low‐Ca pyroxene embedded in Si‐rich glass. The mineralogy and texture of the shocked samples are similar to those of some types of micrometeorites. In particular, the samples shocked at 10 and 21 GPa are similar to the phyllosilicate (serpentine)‐rich micrometeorites, and the sample shocked at 49 GPa is similar to the olivine‐rich micrometeorites. The shock heating effects also resemble the effects of pulse‐heating experiments on the CI and CM chondrite matrices that were conducted to simulate atmospheric entry heating. We suggest that micrometeorites derived from porous asteroids are likely to go through both shock and atmospheric‐entry heating processes. 相似文献