Earth Science (Chikyu Kagaku)

Bottom Topography of the East Pacific Rise(Photo)

Akira SUGIYAMA

Article type: Article
2006 Volume 60 Issue 6 Pages 451-452
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_451

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Introduction to the special issue on the Damage and geological setting of The Mid Niigata Prefecture Earthquake 2004(<Special issue>Damage and geological setting of The Mid Niigata Prefecture Earthquake 2004)

Committee of special issue of the Mid Niigata Prefecture Earthquake

Article type: Article
2006 Volume 60 Issue 6 Pages 453-454
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_453

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Factors of earthquake damage in terrace and alluvial lowland areas of the Mid Niigata Prefecture Earthquake 2004 in the Yukyuzan area, Nagaoka city -Damage control by valley-shaped low grounds and ditches- (<Special issue>Damage and geological setting of The Mid Niigata Prefecture Earthquake 2004)

Yoshihiro KUBOTA, Kosuke YAMAZAKI, Kensho IIKAWA, Masakatsu YOSHIKOSHI

Article type: Article
2006 Volume 60 Issue 6 Pages 455-464
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_455

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The Mid Niigata Prefecture Earthquake on 23 Oct. in 2004 caused the extensive damage to houses and the ground. The results of the extra survey on the relationship between the earthquake damage and geologic setting in the Yukyuzan area, Nagaoka city, are as follows: (1) Why did house damages concentrate within a zone on a terrace surface which is generally assumed to be stable?; Valley-shaped low grounds are confirmed on the Lower terraces where residential areas are in the studied area. The damage was concentrated along the embankment areas of bottom and slope in the valley-shaped low grounds. Geologic factors of the damage were inferred that alluvial muddy deposits and embankment displaced to the lower slope. (2) Why did the damage of the new town occurred sporadically on the ground of embankment in alluvial lowland? The damage distributed in the zone controlled by the ditch beside houses. The ditch was the old irrigation channel. The ground of residential areas inclines toward the northwest by the down slope of 0.7/100. The damage was concentrated in the downstream area of thick embankment and deep ditches, around one meter. The deformed or broken ditches beside damaged houses did not have a cover. The over earth pressure by the seismic vibration in the inclined residential grounds caused that the embankment was displaced with houses and pushed the wall of open ditches. Thereby the houses were seriously damaged by the seismic shock. Housing-land development will increasingly go toward the alluvial lowland in the future. It is important to take precautions against the ground displacement due to the seismic vibration, for example, enhancement of the breast wall of embankment and the sidewall of ditches, and installation of a steel or concrete cover on ditches, to resist against a seismic shock.

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The Collapse Basin on the Latest Pleistocene -Tamugiyama Collapse Basin in the northern part of Uonuma Hills, central Japan- (<Special issue>Damage and geological setting of The Mid Niigata Prefecture Earthquake 2004)

Neotectonics Research Group of the Niigata Shinano River Region

Article type: Article
2006 Volume 60 Issue 6 Pages 465-479
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_465

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This paper shows that the Tamugiyama Basin was formed during the Latest Pleistocene by repeated uplift and collapse fault activities. The Tamugiyama Collapse Basin is the youngest one, has ever been reported collapse basins in the Japanese Islands. The Tamugiyama Collapse Basin is located in the northern part of Uonuma Hills, and is attacked by the 2004 Niigata Chuetsu earthquake. The lozenge-shaped basin, about one to two kilometers wide, is surrounded by hills composed of the Pliocene basement. The Tamugiya Formation within this collapse basin is in high-angle abut unconformity contact with Pliocene basement. Talus deposits are recognized on the unconformities. The deposits are resulted from fault scarp and its ancient slope failures. The Tamugiyama Formation is composed of irregularly alternating beds of gravels, sands and silts, intercalated with the Aira Tn tephra bed (AT) about 26,000〜29,000 years ago. The formation contains peat layers, which characterize static slack-water environments. The Kowakita Formation, underlying the Tamugiyama Formation, consists of fluvial gravels carried by the Uono River, therefore it suggests that there was once the ancient Uono River running through this area. The rapid change in sedimentary environments, from the Kowakita formation to the Tamugiyama Formation, results from uplift, faulting and collapse caused by tectonic block movements in this area. The Uono River had changed its course by fault activity and uplift just before the Tamugiyama Collapse Basin was formed, not by subsidence of the present Uono River course. The Yamamotoyama tectonic block including this study area has been the most active uplift block in the Shinano Valley since the Late Pleistocene. The 2004 Niigata Chuetsu earthquake occurred in areas characterized by the same geological setting.

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Relationship between damages by the 2004 mid-Niigata Prefecture Earthquake and thickness of fan deposits in Tamugiyama area, Kawaguchi Town, Niigata Prefecture, central Japan(<Special issue>Damage and geological setting of The Mid Niigata Prefecture Earthquake 2004)

Yoshinori MIYACHI, Taku KOMATSUBARA, Tsutomu NAKAZAWA, Rei NAKASHIMA, ...

Article type: Article
2006 Volume 60 Issue 6 Pages 481-487
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_481

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The Tamugiyama district in Kawaguchi Town, Niigata Prefecture is one of the most affected areas by the 2004 mid-Niigata prefecture Earthquake. However, the damage distribution shows regional difference within the Tamugiyama district. The worst-hit colony is located on the alluvial fan underlain by thick (ca.20m) muddy deposits. The fan deposits are soft with the N values from 5 to 20 and the low S wave velocity (<200m/sec.). On the other hand, the basement rocks and the terrace deposits are hard with the N values over 50 and the high S wave velocity (>600m/sec.). The peculiar cycle of the fan deposits is calculated at about 0.5 seconds. This is mostly same as that of wooden houses. The serious damages, therefore, seem to have caused by this peculiar cycle. It is generally thought that there is little amplification of the seismic motion on alluvial fans because deposits beneath most alluvial fan consist of gravels. However, Chuetsu area including the Tamugiyama district, the peculiar fan deposits composed mainly of soft muddy deposits much amplified seismic motion of the earthquake.

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Geologic condition of the occurrence of the Mid-Niigata Prefecture Earthquake in 2004(<Special issue>Damage and geological setting of The Mid Niigata Prefecture Earthquake 2004)

Yasumoto SUZUKI, Ikuo HARADA

Article type: Article
2006 Volume 60 Issue 6 Pages 489-500
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_489

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The Mid-Niigata Prefecture Earthquake (M6.8) occurred along Higashiyama anticline on October 23, 2004, accompanying anticlinal deformation attaining maximum upheaval of 60cm or more (Fig2). Isoseismals based on the scale of JMA (Japan Meteorological Agency) were shown in Fig. 1, and the damaged areas were observed in several places in the south part of Northeast Honshu. The seismicity in the area had been activated since the North-Miyagi Earthquake (M6.4) occurred on July 26, 2003 (Fig5 and 6) and shallow earthquakes including the Mid-Niigata Prefecture earthquake took place on the environs of the backbone range, where intermediate earthquakes occurred, suggesting vertical deep faults surrounding the backbone range. Seismicity has been also active in Kanto Plain and the sea off those areas. Historical record from the 1800's to 1950 showed the simultaneous and intermittent activity in the south part of Northeast Honshu for some tens to 20 years or so. The strain analysis deduced from displacements of triangulation stations indicates the areas of large maximum shear greater than 10_-5 in which not only shallow destructive earthquakes but intermediate ones have occurred, so the sheared areas must spread vertically their roots down to the areas where the intermediate earthquakes take place. Judging from those data, the earthquake prediction must be based on the measurement of crustal deformation and the observation of seismicity in those wide area.

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New and significant outcrop of the Aoba Eastern Fault cutting the lower terrace gravel, Aobayama Hill, Sendai, northeast Japan

Soichi OSOZAWA, Osamu SASAKI, Satoshi KANISAWA

Article type: Article
2006 Volume 60 Issue 6 Pages 501-505
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_501

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The reverse fault, corresponding to the contractional bend of the sinistral Aoba Eastern Fault, cuts the lower taracce gravel at the new outcrop of the Tohoku Institute of Technology Aobayama playground. Another old outcrop shows that the reverse faults, also a part of the Aoba Eastern Fault, crosscut the Aobayama terrace deposit and the Adachi-Medeshima pumice deposit. The Aoba Eastern Fault at the Aobayama Hill is confirmed to be an active fault.

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An occurrence of the Nanaura Unconformity from Plio : Pleistocene in Sasagami Hills, the eastern margin of Echigo Plain, central Japan

Mitsuru INABA, Nobuyuki TAKAHAMA, Satoshi YASUI, Fumio AKIBA, Shinichi ...

Article type: Article
2006 Volume 60 Issue 6 Pages 507-512
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_507

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A new outcrop of unconformity was found in the Pliocene Annogawa Formation at the Sasagami Hills located to the east of the Niigata Plain. This unconformity is named the Nanaura Unconformity. The Annogawa Formation is divided into two formations, namely the Sasagami-Dainichi and Sasagami-Nanaura Formations in ascending order. These formations consist of marine muddy sediments. The Sasagami-Dainichi Formation ranges from late Miocene to late Pliocene in age according to diatom biostratigraphy. Though maker diatom fossils were not yet obtained in the Sasagami-Nanaura Formation, its geological age is probably in Pleistocene, judging from the occurrence of some planctonic foraminiferal maker beds in several wells around the Sasagami Hills, The Nanaura Unconformity indicates a local upheaval movement had occurred in the Niigata sedimentary basin during Plio-Pleistocene age. It proposes new point of view for exploration of oil and natural gas in the subsurface strata of Echigo Plain.

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Hayasaka Ichiro : A pioneer of Actuo-Paleontologie in Japan(Geoscientist)

Toshiaki OSADA

Article type: Article
2006 Volume 60 Issue 6 Pages 513-516
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_513

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Introduction to the International Geological-Geophysical Atlas of the Pacific Ocean (3) East Pacific Rise (Introduction)

Akira SUGIYAMA

Article type: Article
2006 Volume 60 Issue 6 Pages 517-522
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_517

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Unidirectional Solidification Texture

Yasushi WATANABE

Article type: Article
2006 Volume 60 Issue 6 Pages 523-524
Published: November 25, 2006
Released on J-STAGE: July 14, 2017

DOIhttps://doi.org/10.15080/agcjchikyukagaku.60.6_523

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