Refine your search:     
Report No.
 - 
Search Results: Records 1-14 displayed on this page of 14
  • 1

Presentation/Publication Type

Initialising ...

Refine

Journal/Book Title

Initialising ...

Meeting title

Initialising ...

First Author

Initialising ...

Keyword

Initialising ...

Language

Initialising ...

Publication Year

Initialising ...

Held year of conference

Initialising ...

Save select records

Journal Articles

Electrical resistivity structure and helium isotopes around Naruko Volcano, northeastern Japan and its implication for the distribution of crustal magma

Asamori, Koichi; Umeda, Koji; Ogawa, Yasuo*; Oikawa, Teruki*

International Journal of Geophysics, 2010, 7 Pages, 2010/10

The two-dimensional electrical resistivity structure beneath Naruko Volcano was determined using magnetotelluric soundings. The resulting model shows that a prominent conductor exists in the crust beneath the volcano. The location of the conductor agrees closely with a seismic low-velocity zone. Hypocenters of low-frequency micro-earthquakes are located adjacent to the conductor. The cut-off depth of shallow micro-earthquakes becomes shallow toward the west side of the volcanic center and it is coincident with the upper boundary of the conductor. Furthermore, new helium isotope data from hot springs around the volcano were obtained. The high $$^{3}$$He/$$^{4}$$He ratios are obtained near the volcano. The maximum $$^{3}$$He/$$^{4}$$He ratio is located in proximity to this peak and decrease toward away from the volcanic center. This supports the likelihood of mantle-derived materials supplying beneath the volcano. These results indicate that the conductor beneath the volcano is due to high-temperature fluids consisting of magma and related aqueous fluids.

Journal Articles

Re-$$^{14}$$C dating of wood fossils from the gravel beds at Sebadani, the upper reaches of Azusa River, central Japan

Oikawa, Teruki*; Sasao, Eiji; Hoshino, Yasuharu*

Dai Yonki Kenkyu, 47(6), p.425 - 431, 2008/12

The depositional age of gravel beds at the Sebadani, in the upper reaches of Azusa River at the Hida Mountain Range has been determined by AMS $$^{14}$$C dating. We measured the four new AMS $$^{14}$$C dating of wood fossils in the gravel beds of Sebadani. The previous study estimated that the formation age of this gravel beds is 70,000-50,000 yr BP which corresponds to marine isotope stage (MIS) 4. However, the new obtained ages were ${it ca}$. 48 ka BP from the wood fossils in the gravel beds.

Journal Articles

Multiple lines of evidence for crustal magma storage beneath the Mesozoic crystalline Iide Mountains, Northeast Japan

Umeda, Koji; Asamori, Koichi; Ninomiya, Atsushi; Kanazawa, Sunao; Oikawa, Teruki

Journal of Geophysical Research, 112(B5), p.B05207_1 - B05207_9, 2007/05

It has been recognized that the Iide Mountains in Northeast Japan are unique because of their occurrence in a non-volcanic region yet hot springs have anomalously high heat discharge values similar to the heart discharge from hot springs in volcanic regions. In order to attempt to constrain the heat source of hydrothermal activity in the region, new helium isotopic data from hot springs surrounding the Iide Mountains was obtained. The $$^{3}$$He/$$^{4}$$He ratios of the hot spring gases sampled range from 0.22 to 7.9 RA, and the highest ratio is similar to MORB-type helium (8 $$pm$$ 1 RA), indicating a significant contribution of primordial mantle-derived helium. Estimation of post-intrusive radiogenic ingrowth of $$^{4}$$He by decay of U and Th suggests that the heat source beneath the Iide Mountains is not likely ancient magma intruded in the Middle Miocene but newly ascending magma derived from mantle material. The geographical distribution of $$^{3}$$He/$$^{4}$$He ratios of hot spring gases reveals that crustal magma storage exists beneath the Kitamata-dake, one of the peaks of the Iide Mountains. This can be used to interpret the geophysical anomalies in this region such as crustal seismicity and results of magnetotelluric imaging.

Journal Articles

Temporal-spatial variations of Plio-Pleistocene volcanic activity in the Ryohaku Mountains, cental Japan; Evidences from K-Ar ages

Tanase, Atsushi*; Oikawa, Teruki*; Ninomiya, Atsushi; Hayashi, Shintaro*; Umeda, Koji

Kazan, 52(1), p.39 - 61, 2007/02

Temporal and spatial variations on Plio-Pleistocene volcanism in the Ryohaku Mountains, central Japan, have been investigated by newly obtained K-Ar ages on 38 groundmass samples separated from volcanic rocks. The volcanoes in the Ryohaku Mountains form two volcanic rows of the Kuzuryu and hakusan Volcanic Chains which have ESE-WNW and N-S alignments, respectively. Early volcanic activity occurred intermittently from 3.6 Ma to 1.5 Ma, and the volcanoes near the junction of the two volcanic chains were active. The volcanic activity in the ESE-WNW trending Kuzuryu Volcanic Chain was restricted in the age range from 1.2 Ma to 0.7 Ma with migration from Eboshi-Washigatake Volcano (ESE end) to Hoonji Volcano (WNW end). The N-S trending Hakusan Volcanic Chain was active from 0.4 Ma to the present.

Journal Articles

Variations in the $$^{3}$$He/$$^{4}$$He ratios of hot springs on Shikoku Island, Southwest Japan

Umeda, Koji; Kanazawa, Sunao; Kakuta, Chifumi*; Asamori, Koichi; Oikawa, Teruki

Geochemistry, Geophysics, Geosystems (Internet), 7(4), p.Q04009_1 - Q04009_11, 2006/04

New helium isotopic data from hot springs on Shikoku Island with much denser sampling than previous studies were obtained, in order to elucidate the geographical distribution of $$^{3}$$He/$$^{4}$$He ratios in the fore-arc regions of Southwest Japan. Systematic, regional variations in $$^{3}$$He/$$^{4}$$He ratios were observed on both Sikoku Island and the Kii Peninsula. Most of the hot springs having $$^{3}$$He/$$^{4}$$He ratios in the range 1.0 RA to 2.0 RA were determined throughout Shikoku Island. On the other hand, the majority of hot springs in the Kii Peninsula have $$^{3}$$He/$$^{4}$$He ratios higher than 2.0 RA. It has been suggested by some authors that the anomalously high $$^{3}$$He/$$^{4}$$He ratios in the fore-arc region of Southwest Japan are related to the migration of mantle-derived helium with aqueous fluids generated by dehydration of the subducting PHS and mixing with terrestrial waters [e.g., Matsumoto et al., 2003]. According to recent seismological observations of crustal microearthquakes and their focal mechanisms, the geotectonic environment beneath Shikoku Island is subject to a stress field without normal faulting and the extremely low crustal seismicity, which does not favor migration of aqueous fluids from the subcrustal lithosphere, resulting in a relatively small influence of MORB-type helium at surface. As a consequence, the regional variation in $$^{3}$$He/$$^{4}$$He ratios of hot springs on Shikoku Island are interpreted as a three-component mixture of mantle-derived helium associated with magmatism of Middle Miocene of age ($$<$$ 3.4 RA), crustal, radiogenic helium and atmospheric helium.

Journal Articles

Unusual cooling of the Middle Miocene Ichifusayama Granodiorite, Kyushu, Japan

Oikawa, Teruki; Umeda, Koji; Kanazawa, Sunao; Matsuzaki, Tatsuji*

Journal of Mineralogical and Petrological Sciences, 101(1), p.23 - 28, 2006/02

 Times Cited Count:2 Percentile:4.3(Mineralogy)

The authors report biotite K-Ar, zircon FT, and apatite FT ages from four sites in the Ichifusayama Granodiorite in the Outer Zone acidic rocks of Southwest Japan, Southern Kyushu. All the K-Ar ages and FT ages are concentrated on 13-10Ma. The difference in the apatite FT ages was caused by an influence of paleotopography such as a deep valley. The rapid cooling of the granodiorite in ca. 13 Ma occurred by uplift throughout the Outer Zone of Southwest Japan in Kyushu. It is considered that obduction to the Philippine Sea Plate of the Outer Zone of Kyushu also occurred in ca. 13 Ma. It is considered that obduction to the Philippine Sea Plate of the Outer Zone of Kyushu also occurred in ca. 13 Ma.

Journal Articles

Aqueous fluids derived from a subducting slab: Observed high $$^{3}$$He emanation and conductive anomaly in a non-volcanic region, Kii Peninsula, southwest Japan

Umeda, Koji; Ogawa, Yasuo*; Asamori, koichi; Oikawa, Teruki

Journal of Volcanology and Geothermal Research, 149(1-2), p.47 - 61, 2006/01

 Times Cited Count:41 Percentile:70.99(Geosciences, Multidisciplinary)

Aqueous fluids derived from the subducting slab: observed high $$^{3}$$He emanation and cinductive anomaly in a non-volcanic region, Kii Peninsula, southwest Japan

Journal Articles

K-Ar ages of the Lavas from Kirigamine Volcano, Central Japan

Oikawa, Teruki; Nishiki, Kuniaki*

Kazan, 50(2), p.143 - 148, 2005/05

The authors will report two K-Ar ages of volcanic rocks from the Kirigamine Volcano, which composes the uppermost part of the Enrei Formation. Based on the newly obtained ages, previously reported radiometric ages, and volcanostratigraphic data, we identify activity periods of 1.3 to 0.75Ma for Kirigamine Volcano. And, we estimate that the Oiwake Volcanic Graben field by Kirigamine Volcano formed rapidly at ca 0.85Ma. Judging from the previous studies and this study, the duration of the activity of the Enrei Formation is mainly ca.1.5 to 0.75 Ma.

Journal Articles

Rapid uplifting of the northern part of Hida Mountain Range at 1 Ma, based on lithofacies and petrography in the Iyari Formation

Oikawa, Teruki; Wada, Hajime*

Chishitsugaku Zasshi, 110(9), p.528 - 535, 2004/09

None

Journal Articles

Geotectonic environment of the geothermal area in the non-volcanic region, southwest Japan

Umeda, Koji; Asamori, Koichi; Oikawa, Teruki; Kakuta, Chifumi; Zhao, N.*; Kamaya, Noriko*

Gekkan Chikyu, 26(6), p.407 - 413, 2004/06

None

Oral presentation

Cooling history of granitic rocks in Kashiwazima district, western Shikoku

Oikawa, Teruki; Umeda, Koji; Matsuzaki, Tatsuji*

no journal, , 

K-Ar and FT analyses were carried out on biotite, zircon and apatite from the granitic rocks in Kashiwazima district, western Shikoku in order to reveal the cooling history. These ages suggest rapid cooling of the granitic rocks in the temperature range to 100$$^{circ}$$C from 300$$^{circ}$$C in 14-13Ma.

Oral presentation

A Study on the volcanic scenario adapting the FEP analysis; Application to the eruption of Izu-Oshima volcano

Murakami, Makoto*; Kawamura, Makoto; Sasaki, Hisashi*; Makino, Hitoshi; Seo, Toshihiro; Nishimura, Takuya*; Umeda, Koji; Oi, Takao; Geshi, Nobuo*; Oikawa, Teruki*

no journal, , 

The volcanic scenario has mainly been conventionally examined from a viewpoint of empiricism based on the understanding of physics and/or scientific mechanism of volcanic activity. However, when a volcanic scenario is examined only based on the empiricism of a volcano, there is a possibility that the phenomena which the volcano had not experienced in the past may fall out from the scenario. Therefore, it is necessary to follow up omission by collecting information from various volcanoes. The purpose of this research is to develop the scenario analysis technique which can perform prediction of progress of volcanic activity by applying the FEP analysis technique examined by High level radioactive waste geological disposal. As a result, a volcanic scenario can be built by applying the FEP analysis technique. It was understood that the FEP analysis technique developed by geological isolation can apply also to the field of other technology. We will collect information further and apply this technique to other volcanoes. We consider improvement of the FEP analysis technique based on the result of this study.

Oral presentation

A Study on a methodology of volcanic scenario analysis applying FEP analysis

Murakami, Makoto*; Kawamura, Makoto; Makino, Hitoshi; Geshi, Nobuo*; Oikawa, Teruki*; Sasaki, Hisashi*; Seo, Toshihiro; Nishimura, Takuya*; Umeda, Koji; Oi, Takao

no journal, , 

no abstracts in English

Oral presentation

A Study on a methodology of volcanic scenario analysis applying FEP analysis; A Case study

Murakami, Makoto*; Kawamura, Makoto*; Makino, Hitoshi; Geshi, Nobuo*; Oikawa, Teruki*; Nishimura, Takuya*; Umeda, Koji; Sasaki, Hisashi*; Seo, Toshihiro; Oi, Takao*

no journal, , 

The prediction technique of the volcanism is requested from the viewpoint of disaster prevention now. The prediction method using the volcanic scenario has been paid to attention. The purpose of this study is to develop the methodology of the volcanic scenario construction that the progress of the volcanic activity is predictable by progressively applying the FEP analysis methodology in the research of HLW geological disposal to the volcanic activity. A basic concept is as follows. We resolve the phenomena to compose the volcanic activity to the single-process referring to past volcanic eruptions. The single-process is arranged to the logical function theory. And, the development of volcanic scenarios is expressed as a chain of the functions. As a result, we developed adaptable volcano scenarios to the purpose. Moreover, it could be expected that the observations are made more effective by feeding back this methodology to the field survey.

14 (Records 1-14 displayed on this page)
  • 1