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Muographic mapping of the subsurface density structures in Miura, Boso and Izu peninsulas, Japan.

Tanaka HK - Sci Rep (2015)

Bottom Line: While the benefits of determining the bulk density distribution of a landmass are evident, established experimental techniques reliant on gravity measurements cannot uniquely determine the underground density distribution.We also observed a significant reduction in density along fault lines and interpreted that as due to the presence of multiple cracks caused by mechanical stress during recurrent seismic events.We show that this new type of muography technique can be applied to estimate the terrain density and porosity distribution, thus determining more precise Bouguer reduction densities.

View Article: PubMed Central - PubMed

Affiliation: Earthquake Research Institute, The University of Tokyo, 113-0032 Tokyo.

ABSTRACT
While the benefits of determining the bulk density distribution of a landmass are evident, established experimental techniques reliant on gravity measurements cannot uniquely determine the underground density distribution. We address this problem by taking advantage of traffic tunnels densely distributed throughout the country. Cosmic ray muon flux is measured in the tunnels to determine the average density of each rock overburden. After analyzing the data collected from 146 observation points in Miura, South-Boso and South-Izu Peninsula, Japan as an example, we mapped out the shallow density distribution of an area of 1340 km(2). We find a good agreement between muographically determined density distribution and geologic features as described in existing geological studies. The average shallow density distribution below each peninsula was determined with a great accuracy (less than ±0.8%). We also observed a significant reduction in density along fault lines and interpreted that as due to the presence of multiple cracks caused by mechanical stress during recurrent seismic events. We show that this new type of muography technique can be applied to estimate the terrain density and porosity distribution, thus determining more precise Bouguer reduction densities.

No MeSH data available.


Related in: MedlinePlus

Muographic density mapping of Miura Peninsula.(a), location of the observation points in Miura Peninsula. The observation points are grouped according to the different geological features: A, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); B, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago); C, Kinugasa active fault segment; D, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); and E, Kitatake active fault segment; F, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago). Gray dashed lines indicate geological boundaries, and blue bold lines are active fault lines (the data were taken from The AIST (National Institute of Advanced Industrial Science and Technologies) Geological Map). The numbers indicate the observation point ID number (#1-#43). Actual point resolution of the measurements (that ranges between 20–100 m) is much smaller than the size of the circles on the map. Density observed at each observation point is shown with different colors ranging from low-density (blue) to high density (red). The enlarged maps show detailed views of the observation points (b) #27 and #28, (c) #30 and #33, and (d) #31, #34, #37 and #40. The plot of observed densities with error bars (1σ) as a function of the observation point ID number is shown in (e). Capital letters shown in this plot correspond to the Miura Peninsula map (a). H.K.M.T. drew the map and holds the copyright. The dotted lines show the region used for plotting Fig. 10.
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f5: Muographic density mapping of Miura Peninsula.(a), location of the observation points in Miura Peninsula. The observation points are grouped according to the different geological features: A, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); B, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago); C, Kinugasa active fault segment; D, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); and E, Kitatake active fault segment; F, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago). Gray dashed lines indicate geological boundaries, and blue bold lines are active fault lines (the data were taken from The AIST (National Institute of Advanced Industrial Science and Technologies) Geological Map). The numbers indicate the observation point ID number (#1-#43). Actual point resolution of the measurements (that ranges between 20–100 m) is much smaller than the size of the circles on the map. Density observed at each observation point is shown with different colors ranging from low-density (blue) to high density (red). The enlarged maps show detailed views of the observation points (b) #27 and #28, (c) #30 and #33, and (d) #31, #34, #37 and #40. The plot of observed densities with error bars (1σ) as a function of the observation point ID number is shown in (e). Capital letters shown in this plot correspond to the Miura Peninsula map (a). H.K.M.T. drew the map and holds the copyright. The dotted lines show the region used for plotting Fig. 10.

Mentions: Figs. 5, 6 and 7 show muon-deduced maps of above-tunnels density distributions in Miura, South-Boso and South-Izu peninsulas, respectively. These plots are overlaid with indications of active faults212226, geological boundary lines20 (Fig. 8), and old fault lines (considered nearly or completely inactive) drawn for reference. Insets of each figure show plots of derived density with 1σ error bars as a function of the tunnel identification (ID) number and the magnified maps for a greated detail. Specific results from each peninsula will be more extensively discussed in the following subsections.


Muographic mapping of the subsurface density structures in Miura, Boso and Izu peninsulas, Japan.

Tanaka HK - Sci Rep (2015)

Muographic density mapping of Miura Peninsula.(a), location of the observation points in Miura Peninsula. The observation points are grouped according to the different geological features: A, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); B, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago); C, Kinugasa active fault segment; D, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); and E, Kitatake active fault segment; F, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago). Gray dashed lines indicate geological boundaries, and blue bold lines are active fault lines (the data were taken from The AIST (National Institute of Advanced Industrial Science and Technologies) Geological Map). The numbers indicate the observation point ID number (#1-#43). Actual point resolution of the measurements (that ranges between 20–100 m) is much smaller than the size of the circles on the map. Density observed at each observation point is shown with different colors ranging from low-density (blue) to high density (red). The enlarged maps show detailed views of the observation points (b) #27 and #28, (c) #30 and #33, and (d) #31, #34, #37 and #40. The plot of observed densities with error bars (1σ) as a function of the observation point ID number is shown in (e). Capital letters shown in this plot correspond to the Miura Peninsula map (a). H.K.M.T. drew the map and holds the copyright. The dotted lines show the region used for plotting Fig. 10.
© Copyright Policy - open-access
Related In: Results  -  Collection

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f5: Muographic density mapping of Miura Peninsula.(a), location of the observation points in Miura Peninsula. The observation points are grouped according to the different geological features: A, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); B, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago); C, Kinugasa active fault segment; D, middle or late Miocene marine or non-marine sediments (formed between 15 and 7 million years ago); and E, Kitatake active fault segment; F, late Eocene or early Miocene accretionary complex (formed between 40 and 22 million years ago). Gray dashed lines indicate geological boundaries, and blue bold lines are active fault lines (the data were taken from The AIST (National Institute of Advanced Industrial Science and Technologies) Geological Map). The numbers indicate the observation point ID number (#1-#43). Actual point resolution of the measurements (that ranges between 20–100 m) is much smaller than the size of the circles on the map. Density observed at each observation point is shown with different colors ranging from low-density (blue) to high density (red). The enlarged maps show detailed views of the observation points (b) #27 and #28, (c) #30 and #33, and (d) #31, #34, #37 and #40. The plot of observed densities with error bars (1σ) as a function of the observation point ID number is shown in (e). Capital letters shown in this plot correspond to the Miura Peninsula map (a). H.K.M.T. drew the map and holds the copyright. The dotted lines show the region used for plotting Fig. 10.
Mentions: Figs. 5, 6 and 7 show muon-deduced maps of above-tunnels density distributions in Miura, South-Boso and South-Izu peninsulas, respectively. These plots are overlaid with indications of active faults212226, geological boundary lines20 (Fig. 8), and old fault lines (considered nearly or completely inactive) drawn for reference. Insets of each figure show plots of derived density with 1σ error bars as a function of the tunnel identification (ID) number and the magnified maps for a greated detail. Specific results from each peninsula will be more extensively discussed in the following subsections.

Bottom Line: While the benefits of determining the bulk density distribution of a landmass are evident, established experimental techniques reliant on gravity measurements cannot uniquely determine the underground density distribution.We also observed a significant reduction in density along fault lines and interpreted that as due to the presence of multiple cracks caused by mechanical stress during recurrent seismic events.We show that this new type of muography technique can be applied to estimate the terrain density and porosity distribution, thus determining more precise Bouguer reduction densities.

View Article: PubMed Central - PubMed

Affiliation: Earthquake Research Institute, The University of Tokyo, 113-0032 Tokyo.

ABSTRACT
While the benefits of determining the bulk density distribution of a landmass are evident, established experimental techniques reliant on gravity measurements cannot uniquely determine the underground density distribution. We address this problem by taking advantage of traffic tunnels densely distributed throughout the country. Cosmic ray muon flux is measured in the tunnels to determine the average density of each rock overburden. After analyzing the data collected from 146 observation points in Miura, South-Boso and South-Izu Peninsula, Japan as an example, we mapped out the shallow density distribution of an area of 1340 km(2). We find a good agreement between muographically determined density distribution and geologic features as described in existing geological studies. The average shallow density distribution below each peninsula was determined with a great accuracy (less than ±0.8%). We also observed a significant reduction in density along fault lines and interpreted that as due to the presence of multiple cracks caused by mechanical stress during recurrent seismic events. We show that this new type of muography technique can be applied to estimate the terrain density and porosity distribution, thus determining more precise Bouguer reduction densities.

No MeSH data available.


Related in: MedlinePlus