Geochemical indicators and seismic phenomena     

Iwasaki  I. 《Bulletin of Volcanology》1975,39(1):82-90

Bulletin of Volcanology - The results obtained from the study of the Atami Geyser. of Hakone Volcano fumaroles, and of Kagai hot springs can be used for the geochemical prediction of ‘great...  相似文献   

Crustal and upper mantle structure in the Ryukyu Island Arc deduced from deep seismic sounding   总被引：4，自引：0，他引：4  

T. Iwasaki  N. Hirata  T. Kanazawa  J. Melles  K. Suyehiro  T. Urabe  L. Möller  J. Makris  H. Shimamura 《Geophysical Journal International》1990,102(3):631-651

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Configuration of the subducting Philippine Sea slab in the eastern part of southwestern Japan with seismic array and Hi-net data     

T. Iidaka  T. Igarashi  T. Iwasaki 《Gondwana Research》2009,16(3-4):504-511

It is important to know the shape of a subducting slab in order to understand the mechanisms of inter-plate earthquakes and the process of subduction. Seismicity data and converted phases have been used to detect plate boundaries. The configuration of the Philippine Sea slab has been obtained at the western part of southwestern Japan. At the eastern part of southwestern Japan, however, the configuration of the Philippine Sea slab has not yet been confirmed. A spatially high-density seismic network makes it possible to detect the boundaries of the Philippine Sea slab. We used a spatially high-density temporal seismic array in the area. The configuration of the Philippine Sea plate is obtained at the eastern part of southwestern Japan using the temporal seismic array and permanent seismic network data and comparing the seismic structure obtained from the results of refraction surveys. The configuration of the Philippine Sea plate obtained by this study does not bend sharply compared to previous models obtained from receiver function analyses. We delineated the upper boundary of the slab to a depth of about 45 km. The weak image of the boundary, which corresponds to the upper mantle reflector beneath the source area of the 2000 Western Tottori earthquake, was detected using the spatially dense array.  相似文献   

Multiple‐indicator study of groundwater flow and chemistry and the impacts of river and paddy water on groundwater in the alluvial fan of the Tedori River,Japan          下载免费PDF全文

Yumi Iwasaki Yoshioka  Kimihito Nakamura  Takanori Nakano  Haruhiko Horino  Ki‐Cheol Shin  Satoko Hashimoto  Shigeto Kawashima 《水文研究》2016,30(16):2804-2816

To investigate the source, flow paths, and chemistry of rich resources of high‐quality, shallow groundwater in the alluvial fan between the Tedori and Sai rivers in central Japan, we analysed stable isotope ratios of H, O, and Sr and concentrations of major dissolved ions and trace elements in groundwater, river water, and paddy water. The ⁸⁷Sr/⁸⁶Sr ratios of the groundwater are related to near‐surface geology: groundwater in sediment from the Tedori River has high ⁸⁷Sr/⁸⁶Sr ratios (>0.711), whereas that from the Sai River in the north of the fan has low ⁸⁷Sr/⁸⁶Sr ratios (<0.711). δ²H and δ¹⁸O values and ⁸⁷Sr/⁸⁶Sr ratios indicate that groundwater in the central and southern fans is recharged by the Tedori River, whereas recharge in the north is from the Sai River. Mg²⁺, Ca²⁺, Sr²⁺, HCO₃^?, and SO₄^2? concentrations and δ²H and δ¹⁸O values in the groundwater are high in the central fan and, except for the northern area, tend to increase with distance from the Tedori River. There are linear relationships between ⁸⁷Sr/⁸⁶Sr ratio and the reciprocal concentrations of Sr²⁺, Mg²⁺, and Ca²⁺. These geochemical characteristics suggest that as groundwater recharged from the Tedori River flows towards the central fan, it mixes with waters derived from precipitation and paddy water that have become enriched in these components during downward infiltration. These results are consistent with our hydrological analysis and numerical simulation of groundwater flow, thus verifying the validity of the model we used in our simulation of groundwater flow. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Ocean Bottom Seismographs used in a crustal study of an area covered with flood-basalt off Lofoten,N. Norway     

R. Mjelde  M.A. Sellevoll  H. Shimamura  T. Iwasaki  T. Kanazawa 《地学学报》1993,5(1):76-84

Seismic refraction measurements were made in August 1988 to study the crustal structure off Lofoten, Northern Norway. Twenty-four 3-component Ocean Bottom Seismographs (OBS) were used, of which seven were deployed in the area covered by landward-flowing basalt deposited during the early Eocene break-up between Norway and Greenland. The main purpose of the OBS survey was to investigate whether this method can be used to map structures below the basalt, which is not easy to penetrate with conventional seismic reflection techniques. The records obtained showed that the OBS data contain considerable information about structures below the flood-basalt; preopening sediments up to 4.0 km thick is indicated below the 1.0–2.5 km-thick landward-flowing basalt. The success of the OBS survey indicates that such measurements can become an important tool in investigations on passive volcanic margins and, potentially, in other areas where highly reflective boundaries make the reflection technique difficult to apply.  相似文献   

The Circulation in the Upper and Intermediate Layers of the South China Sea   总被引：4，自引：0，他引：4  

Atsuhiko Isobe  Takaya Namba 《Journal of Oceanography》2001,57(1):93-104

The circulation in the basin of the South China Sea is reproduced using a four-layer numerical model. Current fields in the second (upper) and third (intermediate) layers are emphasized. Three eddies coexist in the upper layer in summer. The circulation pattern in this layer is similar to that in the first (surface) layer. In winter, a cyclonic circulation occupies the entire basin of the South China Sea in the upper layer as in the surface layer. On the other hand, the circulation pattern in the intermediate layer is fairly different from that in upper two layers especially in winter. A double-gyre pattern appears in the intermediate layer during winter. The pattern is caused by the propagation of the baroclinic Rossby wave of the second mode. This wave is excited at onset of the winter monsoon wind. Such circulation pattern well explains the observed salinity distribution in the intermediate layer. Although the double-gyre pattern in the intermediate layer is revealed even in summer in this model, it is restricted in the western part of the basin. Besides, its current speed is small compared to that in winter.  相似文献   

Stability of genetic diversity in an intertidal goby population after exposure to tsunami disturbance          下载免费PDF全文

Shotaro Hirase  Minoru Ikeda  Shun Hayasaka  Wataru Iwasaki  Akihiro Kijima 《Marine Ecology》2016,37(5):1161-1167

Massive tsunami disturbances have potentially detrimental effects on genetic diversity and effective population size of coastal marine species, and evaluating these effects can be useful for devising conservation strategies for coastal marine environments. Local populations of the intertidal goby Chaenogobius annularis, which are distributed on scattered rocky beaches of the Japanese Archipelago, show demographic independence without overlapping generations, making this an ideal species with which to study the effects of tsunami disturbance on genetic diversity. Some of these populations were affected by the tsunami of the 2011 off the Pacific coast of Tohoku Earthquake. Here, we investigated the change in genetic diversity of a local population of this species, which was located close to the epicenter of the earthquake, across the cohorts before and after the tsunami and evaluated the impact of the tsunami disturbance. Genetic diversity was maintained after the tsunami, and no change in the effective population size was observed. Our results suggest that the tsunami disturbance has had no marked impact on the genetic diversity of C. annularis.  相似文献   

Waves and mean flows,by Oliver Bühler     

Toshiki Iwasaki 《地球物理与天体物理流体动力学》2013,107(4):451-452

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The last deglacial history of Lützow‐Holm Bay,East Antarctica     

Masako Yamane  Yusuke Yokoyama  Hideki Miura  Hideaki Maemoku  Shogo Iwasaki  Hiroyuki Matsuzaki 《第四纪科学杂志》2011,26(1):3-6

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Extinction curves expected in young galaxies     

Hiroyuki Hirashita †‡  Takaya Nozawa  Takashi Kozasa  Takako T. Ishii †  Tsutomu T. Takeuchi § 《Monthly notices of the Royal Astronomical Society》2005,357(3):1077-1087

We investigate the extinction curves of young galaxies in which dust is supplied from Type II supernovae (SNe II) and/or pair instability supernovae (PISNe). We adopt Nozawa et al. (2003) for compositions and size distribution of grains formed in SNe II and PISNe. We find that the extinction curve is quite sensitive to internal metal mixing in supernovae (SNe). The extinction curves predicted from the mixed SNe are dominated by SiO₂ and are characterized by a steep rise from infrared to ultraviolet (UV). The dust from unmixed SNe shows a shallower extinction curve, because of the contribution from large-sized (∼0.1 μm) Si grains. However, the progenitor mass is important in unmixed SNe II: if the progenitor mass is smaller than  ∼20 M_⊙  , the extinction curve is flat in UV; otherwise, the extinction curve rises towards the short wavelength. The extinction curve observed in a high-redshift quasar  ( z = 6.2)  favours the dust production by unmixed SNe II. We also provide some useful observational quantities, so that our model might be compared with future high- z extinction curves.  相似文献