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51.
A tephra layer offers an isochronous surface in sediments, thus serving as a key bed and/or an age marker. Recent high-resolution sediment research (e.g. varved sediments) has revealed optically invisible tephra fingerprints and provided high-precision tephra ages. However, a tephra-based correlation cannot succeed without detailed knowledge of the tephra characteristics in a proximal area to correlate with tephra in high-resolution sediments in remote areas. Here we documented the detailed characteristics of Towada-Chuseri (To-Cu) tephra, which is associated with the Middle Holocene volcanic explosivity index 5 eruption of Towada volcano, northeast Japan. We used To-Cu tephra samples to achieve the proximal–distal correlation of three members: Chuseri pumice (Cu), Kanegasawa pumice (Kn) and Utarube ash (Ut). These distal occurrences correlate with proximal To-Cu tephra based on volcanic glass morphology and refractive index, as well as on major element composition of volcanic glass shards. Refractive indices allow the preliminary correlation of each member, and major element composition helps in distinguishing Ut from the other members. Glass morphology provides additional support. These correlations reveal that To-Cu, especially Cu, covered central to northeast Japan while confirming that To-Cu is the representative tephra in the Middle Holocene of the Tohoku region. 相似文献
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Reconnaissance report on landslide disasters in northeast Japan following the M 9 T��hoku earthquake
Toyohiko Miyagi Daisuke Higaki Hiroshi Yagi Shoji Doshida Noriyuki Chiba Jun Umemura Go Satoh 《Landslides》2011,8(3):339-342
An earthquake of Mw 9.0 struck the Pacific coast in northeast Japan on March 11, 2011 and was followed by a hugely damaging tsunami along 500 km
of the Japanese coastline. An inland aftershock of M. 7.0 occurred on April 11; during which, surface fault ruptures appeared
on land. A large variety of landslide disasters resulted from these earthquakes in various parts of northeastern Honshu, Japan.
The full extent of the landslides is still being determined. This brief report introduces some of the landslide phenomena
so far investigated by the Japanese Landslide Society. These are (1) failure of a water reservoir embankment dam in Sukagawa,
Fukushima prefecture, (2) landslides and surface seismic fault rupture from the April 11 aftershock in Iwaki, Fukushima, (3)
a concentration of surface failures at Matsushima Bay in Miyagi prefecture, and (4) small landslides on modified slopes in
residential areas around Sendai city. 相似文献
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56.
N-body simulations of the Magellanic stream 总被引:1,自引:0,他引:1
Tim W. Connors Daisuke Kawata Brad K. Gibson 《Monthly notices of the Royal Astronomical Society》2006,371(1):108-120
A suite of high-resolution N -body simulations of the Magellanic Clouds–Milky Way system are presented and compared directly with newly available data from the H i Parkes All-Sky Survey (HIPASS). We show that the interaction between Small Magellanic Clouds (SMC) and Large Magellanic Clouds results in both a spatial and kinematical bifurcation of both the stream and the leading arm. The spatial bifurcation of the stream is readily apparent in the HIPASS data, and the kinematical bifurcation is also tentatively identified. This bifurcation provides strong support for the tidal disruption origin for the Magellanic stream. A fiducial model for the Magellanic Clouds (MCs) is presented upon completion of an extensive parameter survey of the potential orbital configurations of the MCs and the viable initial boundary conditions for the disc of the SMC. The impact of the choice of these critical parameters upon the final configurations of the stream and leading arm is detailed. 相似文献
57.
Shoji Kojima María Constanza San Martín Toshiro Nagase Daisuke Nakashima Claudio Bisso Andrew Menzies 《Resource Geology》2021,71(1):80-90
Modes of occurrence of Au‐ and Ag‐bearing phases and their relation with associated hypogene ore minerals were examined with the objective to elucidate Au‐Ag distribution at the Esperanza porphyry deposit in the Eocene Centinela copper belt, using ore‐microscope modal analysis, semi‐quantitative analyses by automated mineralogy, electron probe microanalysis, and secondary ion mass spectrometer. The Esperanza hypogene mineralization is characterized by early‐stage chalcopyrite‐rich veinlets in the potassic alteration zone and later polymetallic stage with tennantite and galena in the chlorite‐sericitic alteration zone. Only the early‐stage chalcopyrite contains fine‐grained electrum (Au68Ag32 ‐ Au81Ag19) and hessite (Ag2Te), and thus yields positive correlations in Cu vs. Au and Cu vs. Ag grades that are clearly recognized in the hypogene sulfide zone. The early‐stage chalcopyrite grains frequently exhibit polysynthetic twinning suggestive of inversion from intermediate solid solution. These features suggest that the fine‐grained electrum and hessite are products exsolved in the cooling process with the intermediate solid solution to chalcopyrite inversion. In contrast, tennantite and galena of the later‐stage mineralization contain no detectable Ag, and it is thus proposed that the early‐stage inverted chalcopyrite is the principal storage of economically important precious metals. 相似文献
58.
Takuya Manaka Hiroyuki Ushie Daisuke Araoka Akihiko Inamura Atsushi Suzuki Hodaka Kawahata 《Aquatic Geochemistry》2013,19(4):281-302
The global carbon cycle, one of the important biogeochemical cycles controlling the surface environment of the Earth, has been greatly affected by human activity. Anthropogenic nutrient loading from urban sewage and agricultural runoff has caused eutrophication of aquatic systems. The impact of this eutrophication and consequent photosynthetic activity on CO2 exchange between freshwater systems and the atmosphere is unclear. In this study, we focused on how nutrient loading to lakes affects their carbonate system. Here, we report results of surveys of lakes in Japan at different stages of eutrophication. Alkalization due to photosynthetic activity and decreases in PCO2 had occurred in eutrophic lakes (e.g., Lake Kasumigaura), whereas in an acidotrophic lake (Lake Inawashiro) that was impacted by volcanic hot springs, nutrient loading was changing the pH and carbon cycling. When the influence of volcanic activity was stronger in the past in Lake Inawashiro, precipitation of volcanic-derived iron and aluminum had removed nutrients by co-precipitation. During the last three decades, volcanic activity has weakened and the lake water has become alkalized. We inferred that this rapid alkalization did not result just from the reduction in acid inputs but was also strongly affected by increased photosynthetic activity during this period. Human activities affect many lakes in the world. These lakes may play an important part in the global carbon cycle through their influence on CO2 exchange between freshwater and the atmosphere. Biogeochemical changes and processes in these systems have important implications for future changes in aquatic carbonate systems on land. 相似文献
59.
Hirotsugu Minami Kazuya Tatsumi Akihiro Hachikubo Satoshi Yamashita Hirotoshi Sakagami Nobuo Takahashi Hitoshi Shoji Young Keun Jin Anatoly Obzhirov Nataliya Nikolaeva Alexander Derkachev 《Geo-Marine Letters》2012,32(5-6):525-534
The Sakhalin Slope Gas Hydrate Project (SSGH) is an international collaborative effort by scientists from Japan, Korea, and Russia to investigate natural gas hydrates (GHs) that have accumulated on the continental slope off Sakhalin Island, Okhotsk Sea. From 2009 to 2011, field operations of the SSGH-09, -10, and -11 projects were conducted. GH-bearing and -free sediment cores were retrieved using steel hydro- and gravity corers. The concentrations of sulfate ions in sediment pore waters were measured to investigate sulfate concentration–depth profiles. Seventeen cores showed linear depth profiles of sulfate concentrations. In contrast, eight cores and two cores showed concave-up and -down profiles plausibly explained by sudden increase and decrease in methane flux from below, respectively, presumably caused by the formation of gas hydrate adjacent to the core sampling sites. 相似文献
60.
Yuki Shibazaki Eiji Ohtani Hiroshi Fukui Takeshi Sakai Seiji Kamada Daisuke Ishikawa Satoshi Tsutsui Alfred Q.R. Baron Naoya Nishitani Naohisa Hirao Kenichi Takemura 《Earth and Planetary Science Letters》2012
We have determined the density evolution of the sound velocity of dhcp-FeHx (x ≈ 1) up to 70 GPa at room temperature, by inelastic X-ray scattering and by X-ray diffraction. We find that the variation of VP with density is different for the ferromagnetic and nonmagnetic dhcp-FeHx, and that only nonmagnetic dhcp-FeHx follows Birch's law. Combining our results with Birch's law for iron and assuming an ideal two-component mixing model, we obtain an upper bound of the hydrogen content in the Earth's inner core, 0.23(6) wt.% H, corresponding to FeH0.13(3). The iron alloy with 0.23(6) wt.% H can satisfy the density, and compressional and shear sound velocities of the PREM inner core, assuming that there are no other light elements in the inner core. 相似文献