Audio frequency magneto-telluric survey of Norikura Volcano in central Japan     

Kiyoshi Fuji-ta  Yasuo Ogawa  Masahiro Ichiki  Satoru Yamaguchi  Yutaka Makino 《Journal of Volcanology and Geothermal Research》1999,90(3-4)

Norikura Volcano has not been active during the last 10,000 years in spite of the activity of the surrounding volcanic mountains. To study past volcanic activities, geological studies were carried out extensively. However, quite a few geophysical investigations were conducted to contribute to volcanology. Our objective is to detect the present subsurface structure of Norikura Volcano and to define volcanic stratifications. In the vicinity of Norikura Volcano, geothermal fields are still active. Subsurface volcanic rocks in this area have been exposed to geothermal activity and altered. To comprehend volcanic stratifications of Norikura and geothermal activity, we conducted audio frequency magneto-telluric (AMT) surveys around Norikura Volcano. AMT survey is useful in clearly defining the resistivity structure related to volcanic regions. The AMT data were acquired over a frequency range 10 Hz–10 kHz. Decomposition analysis was applied to the tensor impedance data. Subsequently, apparent resistivity and phase data were inverted using a two-dimensional magneto-telluric (MT) inversion and a model of Norikura was derived. The final model manifests that the surface resistors are in agreement with andesite lava or dacite lava. As for the deeper structure, a horizontal conductor is situated above resistive basements. The alteration of the conductor was weak, while basement rocks were strongly altered and/or heated through the thermal activity. The existence of these layers seems to indicate the degree of thermal activity of Norikura Volcano.  相似文献   

Positioning fisheries in a changing world   总被引：1，自引：1，他引：0  

R. Quentin Grafton  Ray Hilborn  Lori Ridgeway  Dale Squires  Meryl Williams  Serge Garcia  Theodore Groves  James Joseph  Kieran Kelleher  Tom Kompas  Gary Libecap  Carl Gustaf Lundin  Mitsutaku Makino  Thorolfur Matthiasson  Richard McLoughlin  Ana Parma  Gustavo San Martin  Ben Satia  Carl-Christian Schmidt  Maree Tait  Lin Xiu Zhang 《Marine Policy》2008,32(4):630-634

Marine capture fisheries face major and complex challenges: habitat degradation, poor economic returns, social hardships from depleted stocks, illegal fishing, and climate change, among others. The key factors that prevent the transition to sustainable fisheries are information failures, transition costs, use and non-use conflicts and capacity constraints. Using the experiences of fisheries successes and failures it is argued only through better governance and institutional change that encompasses the public good of the oceans (biodiversity, ecosystem integrity, sustainability) and societal values (existence, aesthetic and amenity) will fisheries be made sustainable.  相似文献   

Relational places of ethnic Burman women migrants in the borderland town of Tachilek, Myanmar     

Kyoko Kusakabe  Zin Mar Oo 《Singapore journal of tropical geography》2007,28(3):300-313

This paper presents an investigation based on the testimonies of ethnic Bamar or Burman women migrant workers in the ethnically diverse 'borderland' town of Tachilek, Myanmar and interviews with their relatives in the home village in the central Burman heartlands. We examine how the concept of relational places, here involving a village in the central Mandalay Division and a town in the Myanmar–Thailand borderland, is related to differential power relations affecting the women migrants. We focus on the ways that gender identity and social position are limited by the relational places of community elders and the migrant women themselves, and suggest that the relational places of migrants in Myanmar are constructed through the nexus of varied forms of state control in both the central Burman heartlands and the multiethnic borderlands of the country.  相似文献   

Seismic study on oceanic core complexes in the Parece Vela back-arc basin   总被引：1，自引：0，他引：1  

Yasuhiko  Ohara  Kyoko  Okino  Junzo  Kasahara 《Island Arc》2007,16(3):348-360

Abstract   In the present study the seismic structure of oceanic core complexes (OCC) in the Parece Vela Basin, Philippine Sea have been imaged. Together with recent work on the Atlantis Massif OCC on the Mid-Atlantic Ridge, including deep drilling, this work provides an unprecedented opportunity to advance our understanding of OCC internal structure. A continuous, strong and relatively smooth reflection that was ca 0.15 s (two way time) below the sea floor of an OCC in the Chaotic Terrain of the Parece Vela Basin was identified. This reflection, termed the D-reflector, is similar to that observed beneath Atlantis Massif. A faster P-wave velocity (>6 km/s) is observed very shallow beneath the Chaotic Terrain OCC, suggesting that the core of these OCC is dominantly gabbroic. The D-reflector might be common beneath OCC, owing to localized alteration along fractured zones within gabbro. We further observed a series of three detachment events in the Chaotic Terrain. The first and second detachments exhumed shallow basaltic crust to deeper gabbroic core, whereas the last one only exhumed shallow basaltic crust.  相似文献   

Time variations of hard X-rays from Sco X-1     

M. Matsuoka  M. Fujii  S. Miyamoto  J. Nishimura  M. Oda  Y. Ogawara  S. Hayakawa  I. Kasahara  F. Makino  Y. Tanaka  P. C. Agrawal  B. V. Sreekantan 《Astrophysics and Space Science》1972,18(2):472-490

Simultaneous hard X-ray and optical observations of Sco X-1 were carried out on 1971 May 1 at Hyderabad, India, when Sco X-1 was optically bright. The X-ray intensity observed by balloon-borne counter telescopes increased in coincidence with optical enhancements, while the plasma temperature derived by fitting the X-ray spectrum in the energy range 20–40 keV to the thermal bremsstrahlung spectrum did not appreciably change over the whole period of observation.  相似文献   

Rocket observation of energy spectrum of diffuse hard X-rays     

Y. Fukada  S. Hayakawa  M. Ikeda  I. Kasahara  F. Makino  Y. Tanaka 《Astrophysics and Space Science》1975,32(1):L1-L5

The energy spectrum of diffuse hard X-rays measured in the range 10–40 keV shows a rather sharp change of slope. The logarithmic derivative of the spectrum changes around 20–30 keV by the increment significantly greater than 0.5 within an interval smaller than 50 keV.  相似文献   

Observation of cosmic soft X-rays     

S. Hayakawa  T. Kato  F. Makino  H. Ogawa  Y. Tanaka  K. Yamashita  M. Matsuoka  S. Miyamoto  M. Oda  Y. Ogawara 《Astrophysics and Space Science》1971,12(1):104-117

Cosmic soft X-rays in the energy range between 0.14 and 7 keV were observed with thin polypropylene window proportional counters on board a sounding rocket. The field of view crossed the galactic plane in the Cygnus-Cassiopeia region at a large angle and reached the galactic latitudes of –55° and +30°. Referring also to the result with Be window counters, we obtained the energy spectrum of Cyg XR-2, the flux from the Cas A region and the distribution of the intensity of diffuse X-rays over the scanned region. The turn-over of the Cyg XR-2 spectrum at about 1 keV indicates that the distance of the Cyg XR-2 source lies between 600 and 800 pc, if the turn-over is due entirely to interstellar absorption. The flux from the Cas A region is obtained as 0.23±0.05 photons cm^–2 sec^–1 in the energy range between 1.1 and 4.1 keV. The intensity of diffuse soft X-rays depends on the galactic latitude more weakly than expected from the interstellar absorption of extragalactic X-rays and shows asymmetry with respect to the galactic equator, thus suggesting a contribution of galactic X-rays. The spectrum of extragalactic X-rays is approximately represented by a power lawE ^–1.8.  相似文献   

Alteration processes recorded by back-arc mantle peridotites from oceanic core complexes,Shikoku Basin,Philippine Sea     

Ken-ichi Hirauchi  Izumi Segawa  Yui Kouketsu  Yumiko Harigane  Yasuhiko Ohara  Jonathan Snow  Atlanta Sen  Masakazu Fujii  Kyoko Okino 《Island Arc》2021,30(1):e12419

We determined the mineralogical and petrological characteristics of ultramafic rocks dredged from two oceanic core complexes: the Mado Megamullion and 23°30′N non-transform offset massif, which are located within the Shikoku back-arc basin in the Philippine Sea. The ultramafic rocks are strongly serpentinized, but can be classified as harzburgite/lherzolite or dunite, based on relict primary minerals and their pseudomorphs. Strongly elongated pyroxene porphyroclasts with undulatory extinction indicate high-temperature (≥700 °C) strain localization on a detachment fault within the upper mantle at depths below the brittle–viscous transition. During exhumation, the peridotites underwent impregnation by magmatic or hydrothermal fluids, lizardite/chrysotile serpentinization at ≤300 °C, antigorite crystallization, and silica metasomatism that formed talc. These features indicate that the detachment fault zones formed a fluid pathway and facilitated a range of fluid–peridotite interactions.  相似文献   

Mobile livelihoods among ethnic minorities in China: Insights from Yunnan     

Yunxian Wang  Kyoko Kusakabe  Ragnhild Lund  Smita Mishra Panda  Qun Zhao 《Norsk geografisk tidsskrift. Norwegian journal of geography》2013,67(4):187-199

Ethnic minority populations in Yunnan have had diverse mobility patterns since the advent of globalized production and developmental programmes. The article presents insights into the various mobility patterns and their effects in Yunnan and contributes to an understanding of the present economic and social processes of mobilities and changes in China as a whole. The analysis is based on an empirical study conducted in the years 2010–2011 by the authors together with local researchers in Yunnan. The results revealed that the mobilities practised among members of the ethnic minority groups in Yunnan included not only outmigration but also cross-border cultivation of plantations, daily and circular mobility, inflows of labour and investors, and involuntary relocation. Although some mobilities may have been conducive to livelihoods and capabilities due to the income-earning and profit-making opportunities arising from the acquisition and appropriation of land and capital, they have also resulted in differentiation processes that confirm the counter-geographies of production, survival, and profit-making. The authors conclude that mobilities do not just concern physical location, but as a social process, mobilities have reconstituted relational references and networks in terms of ethnic and cultural identity, gender relations, labour division, and locality and community integration.  相似文献   

Eocene volcanism during the incipient stage of Izu–Ogasawara Arc: Geology and petrology of the Mukojima Island Group,the Ogasawara Islands     

Kyoko Kanayama  Susumu Umino  Osamu Ishizuka 《Island Arc》2012,21(4):288-316

The Ogasawara Islands mainly comprise Eocene volcanic strata formed when the Izu–Ogasawara–Mariana Arc began. We present the first detailed volcanic geology, petrography and geochemistry of the Mukojima Island Group, northernmost of the Ogasawara Islands, and show that the volcanic stratigraphy consists of arc tholeiitic rocks, ultra‐depleted boninite‐series rocks, and less‐depleted boninitic andesites, which are correlatable to the Maruberiwan, Asahiyama and Mikazukiyama Formations on the Chichijima Island Group to the south. On Chichijima, a short hiatus is identified between the Maruberiwan (boninite, bronzite andesite, and dacite) and Asahiyama Formation (quartz dacite and rhyolite). In contrast, these lithologies are interbedded on Nakodojima of the Mukojima Island Group. The stratigraphically lower portion of Mukojima is mainly composed of pillow lava, which is overlain by reworked volcaniclastic rocks in the middle, whereas the upper portion is dominated by pyroclastic rocks. This suggests that volcanic activity now preserved in the Mukojima Island Group records growth of one or more volcanoes, beginning with quiet extrusion of lava under relatively deep water followed by volcaniclastic deposition. These then changed into moderately explosive eruptions that took place in shallow water or above sea level. This is consistent with the uplift of the entire Ogasawara Ridge during the Eocene. Boninites from the Mukojima Island Group are divided into three types on the basis of geochemistry. Type 1 boninites have high SiO₂ (>57.0 wt.%) and Zr/Ti (>0.022) and are the most abundant type in both Mukojima and Chichijima Island Groups. Type 2 boninites have low SiO₂ (<57.1 wt.%) and Zr/Ti (<0.014). Type 3 boninites have 57.6–60.7 wt.% SiO₂ and are characterized by high CaO/Al₂O₃ (0.9–1.1). Both type 2 and 3 boninites are common on Mukojima but are rare in the Chichijima Island Group.  相似文献