The Last Interglacial deposits at Iwanuma City in the Miyagino Coastal Plain, northeast Honshu, Japan.

Kanisawa, Satoshi; Takeuti, Sadako

doi:10.5575/geosoc.103.402

Cited by 3 publications

(5 citation statements)

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“…The broken line denotes the border between Yamagata and Fukushima prefectures. The black line denotes the rim of the Ohtoge caldera [ Kanisawa et al , ]. (a) Map view.…”

Section: Introductionmentioning

confidence: 99%

“…Terakawa et al [] suggested that this swarm occurred in response to the increase in pore pressure due to the upwelling fluids facilitated by the EW extension associated with the Tohoku‐Oki earthquake. The source area of this swarm is located just beneath the late Miocene Ohtoge caldera and related volcanic structures [ Kanisawa et al , ], which is believed to include shallow igneous bodies with hydrothermal fluids immediately below [ Yoshida et al , ]. In addition, hypocenters in this swarm activity exhibit a distinct migration behavior.…”

Section: Introductionmentioning

confidence: 99%

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Temporal variation of frictional strength in an earthquake swarm in NE Japan caused by fluid migration

2016

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Temporal variations of the fault frictional strength was investigated based on the diversity of focal mechanisms in the source area of the Yamagata‐Fukushima border earthquake swarm, a significant earthquake swarm that occurred in central Tohoku, NE Japan, which started just after the 2011 M9.0 Tohoku‐Oki earthquake. The focal mechanisms of events in this swarm activity were determined using P wave polarity data as well as short‐period (1.5–2.5 Hz) waveform data from the direct P wave. The stress field in the source area of this swarm was estimated by applying stress tensor inversions to these focal mechanism data. Based on the estimated stress field, and under the assumption of uniform stress, we calculated relative frictional strengths for individual focal mechanisms. The calculated relative frictional strengths vary over a wide range, but their average value exhibits a characteristic temporal variation, which is at first small, but steadily increases with time for 100 to 150 days, and then becomes approximately constant. We confirmed this characteristic temporal variation of the average relative frictional strength by assuming the stress to be nonuniform. Similar temporal variations of the average relative frictional strength are obtained for even these cases, confirming the variation. The most likely cause for the observed temporal variation of the average relative frictional strength is the temporal variation of the pore fluid pressure in the source area of the swarm, facilitated by the Tohoku‐Oki earthquake and the subsequent fluid diffusion.

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“…The broken line denotes the border between Yamagata and Fukushima prefectures. The black line denotes the rim of the Ohtoge caldera [ Kanisawa et al , ]. (a) Map view.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Temporal variation of frictional strength in an earthquake swarm in NE Japan caused by fluid migration

2016

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“…Additionally, Pleistocene shallow marine deposits related to the Ac-Md Pumice have been identified in the Iwanuma Oshiwake core (Figs. 3 , 5 J), with the MIS 5e (or MIS 5c) transgression recorded below the alluvium 43 . In this particular case, the strandline may have subsided and formed a buried terrace (Fig.…”

Section: Rapid Emergence and Intermittent Uplift Of Terracesmentioning

confidence: 96%

“…The basement underlying the Sendai Plain is predominantly composed of Pliocene strata, with the exception of specific areas such as the Nagamachi pool core where Pleistocene deposits are present above the Pliocene basement. Another exception is the Iwanuma Oshiwake core 43 (Fig. 3 ), where fragmented Ac-Md pumice is found between the Pliocene basement and the Holocene shallow marine deposits (with the basal gravels of the Holocene being absent) (Fig.…”

Section: Stratigraphy Of Late Quaternary Terraces Hilly Area and Fluv...mentioning

confidence: 99%

The Sendai river terraces monitored the co-seismic mega-thrusting

Osozawa,

Ito

2023

Sci Rep

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We conducted a detailed geological survey of the Sendai region, covering an area of 100 × 50 km. Our survey focused on accurately mapping river terraces, identifying the source volcanoes responsible for intercalated tephras, and locating the Nagamachi-Rifu fault and associated faults. The river terraces were observed and categorized based on their elevation relative to the present river channels. These terraces are predominantly found on the hanging wall of major reverse faults. Each terrace comprises fluvial gravels at the lower levels and eolian loam intercalated with local and regional tephras at higher levels, with the contact age corresponding to the time of emergence. To determine the ages of the terrace gravels, we employed a combination of zircon U–Pb dating, sedimentation rate calculations, and extrapolation techniques. This allowed us to establish the abandonment or emergent dates of the terraces. The formation of these terraces coincided with periods of fault activity, including hanging wall uplift, footwall subsidence, and fault vertical displacement, effectively monitoring the co-seismicity of the Nagamachi-Rifu fault. While we cannot predict the exact timing of future events, it is crucial to remain vigilant regarding the potential occurrence of a significant earthquake triggered by these fault activities.

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“…period, fossiled fauna and microfossils in the sediments on land, as well as on coastal and shallow-water area in the Japanese Islands, have been examined (Igarashi, 1994;Kanisawa and Takeuti, 1997;Kitamura et al, 1997). Nara (1995Nara ( , 1997Nara ( , 1998 have analyzed that the Rosselia socialis-crowded beds in the middle Pleistocene Ichinono alternating beds of sand and mud, Kongochi Formation in the Boso Peninsula were formed in a transgressive systems tract of a high-frequency depositional sequence.…”

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confidence: 99%

A Study of Quaternary Paleoenvironments and Paleobiology in Japan.

Koizumi

1999

Daiyonki-kenkyu

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This article presents that our investigations based on Paleobiology have good progress in understanding how environmental conditions changed and fluctuated during Quaternary, of fossils themselves as well, for these ten years. Major results are as follows: (1) Sedimentary facies and molluscan fossil contents of Quaternary sediments were originated from glacio-eustacy with the period of orbital precession and/or obliquity by the Milankovitch cycles. (2) Four stages in warm molluscan and diatom assemblages were recognized during the Holocene in Hokkaido. They can be correlated with the periods of strong northward inflow of the warm Tsushima were recognized at the Hyperthermal and Last Interglacial age. (4) Tsunami deposits, which consist of sand and sandy gravel with mixed environmental molluscan shells and wood fragments, generated by earthquakes were found along the Boso and Miura peninsulas. (5) A cold-seep chemosynthetic community, which is composed of the articulated bivalves Conchocela bisecta and Lucinoma spectabilis, were found in the lower Pleistocene Koshiba Formation, Yokohama City. (6) Living fossils were observed in seafloor caves, in deep water, or in singular area around spouting thermal spring on the ocean floor.

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The Last Interglacial deposits at Iwanuma City in the Miyagino Coastal Plain, northeast Honshu, Japan.

Cited by 3 publications

References 0 publications

Temporal variation of frictional strength in an earthquake swarm in NE Japan caused by fluid migration

Temporal variation of frictional strength in an earthquake swarm in NE Japan caused by fluid migration

The Sendai river terraces monitored the co-seismic mega-thrusting

A Study of Quaternary Paleoenvironments and Paleobiology in Japan.

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