Reference : A history of mass transport complexes related to earthquake shaking: the case of Lake...
Scientific congresses and symposiums : Poster
Physical, chemical, mathematical & earth Sciences : Earth sciences & physical geography
A history of mass transport complexes related to earthquake shaking: the case of Lake Motosu (Japan).
Lamair, Laura mailto [Université de Liège > Département de géographie > Géomorphologie et Géologie du Quaternaire >]
Hubert, Aurelia mailto [Université de Liège > Département de géographie > Géomorphologie et Géologie du Quaternaire >]
Boes, Evelien [Ghent University > > > >]
Yamamoto, Shinya []
Garrett, Ed [Geological Survey of Belgium > > > >]
Heyvaert, Vanessa [Geological Survey of Belgium > > > >]
Nakamura, Atsunori [6National Institute of Advanced Industrial Science and Technology (AIST) > > > >]
Miyairi, Yosuke [University of Tokyo > Atmosphere and Ocean Research Institute > > >]
Yokoyama, Yusuke [University of Tokyo > Atmosphere and Ocean Research Institute > > >]
De Batist, Marc [Ghent University > > > >]
The 5th International Geologica Belgica Meeting
du 26 au 29 janvier 2017
[en] The QuakeRecNankai project focuses on geological records of paleoearthquakes along the Nankai-Suruga subduction zone, south central Japan. In the framework of the project, we investigated the Fuji Five Lakes, located at the eastern end of the Nankai-Suruga Trough. Here, we present results from Lake Motosu, the deepest of the Fuji Five Lakes (max. depth 122 m), including seismic reflection profiles and gravity cores. We identify mass transport deposits and turbidites possibly triggered by earthquakes. We study the lake sedimentary architecture and the Holocene sedimentation with a very high resolution GEOPULSE pinger system. A seismic grid with total length of 39 km covered the lake. We identify a specific seismic horizon that may be related to the Aokigaraharamarubi lava flow (864 A.D.). Strong reflectors may also correlate with tephra layers from Oniwa-Okuniwa eruptions (620-790 A.D). In the western part of the lake, the seismic reflection profile reveals a change after the proposed Oniwa-Okuniwa eruptions in terms of volume and length of mass transport deposits. Large mass-transport deposits occurring before the eruptions are characterized by chaotic seismic facies. After the eruptions, the mass-transport deposits are much smaller than previously and characterized by transparent seismic facies attributed to a turbiditic flow. Six gravity cores (max. 90cm) provide samples of the lake bottom sediments. In these cores, turbidites were identified based on facies analyses, combined with X-ray scanning, geophysical properties, grain-size analysis, mineralogy and XRF. An age-depth model was established based on radionuclide dating. We compare the timing of sedimentary events in Lake Motosu with a historical catalogue of natural hazards in the Fuji Five Lakes area, including historical records of megathrust earthquakes rupturing the Nankai subduction zone, the Sagami Trough and other earthquakes occurring along inland faults. Several analyses were performed to understand why we have a change in type of mass transport deposit after the eruptions and to define the minimum shaking intensity required to destabilize the slope. To assess slope stability, we investigated the clay content and the clay mineralogy of the slope. Spatial statistics was also performed in order to evaluate the degree of the slope and the accumulation of sediment. We suggest that the presence of a scoria layer might have contributed to slope destabilization.

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