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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.


Average density determined for different rock types.Capital letters indicate rock types: A: accretionary complex formed between 40 and 22 million years ago; B: marine and non-marine sediments formed between 15 and 1.7 million years ago; C: marine and non-marine sediments formed between 1.7 and 0.7 million years ago; D: basaltic and andesitic rock formed between 7 and 1.7 million years ago.
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f9: Average density determined for different rock types.Capital letters indicate rock types: A: accretionary complex formed between 40 and 22 million years ago; B: marine and non-marine sediments formed between 15 and 1.7 million years ago; C: marine and non-marine sediments formed between 1.7 and 0.7 million years ago; D: basaltic and andesitic rock formed between 7 and 1.7 million years ago.

Mentions: Fig. 9 compares the average densities determined by using data points in different geological domains as indicated with dashed lines in Figs. 4, 5, and 6: (A) accretionary complex formed between 40 and 20 million years ago (2.79 ± 0.05 g/cm3); (B) marine and non-marine sediments formed between 15 and 1.7 million years ago (2.57 ± 0.03 g/cm3); (C) marine and non-marine sediments formed between 1.7 and 0.7 million years ago (2.43 ± 0.05 g/cm3); and (D) basaltic and andesitic rock formed between 7 and 1.7 million years ago (2.51 ± 0.05 g/cm3). The data collected from different regions with identical rock types were merged and averaged to attain better statistics. We can see that as a general trend, the density tends to be higher for older rock, and these values are consistent with gravimetrically determined density values reported by Nawa et al. (1997)3: 2.63 ± 0.09 g/cm3, 2.54 ± 0.15 g/cm3, and 2.58 ± 0.2 g/cm3 respectively for Mesozoic, Tertiary, and Quaternary sedimentary rocks and 2.53 ± 0.15 g/cm3 for Tertiary volcanic rock. As described in the following subsections, the data points located on the fault line were excluded in this plot. Overall, higher density rocks are detected in older geological domains. A closer inspection of Figure 7 reveals an interesting density gap between tertiary and quaternary sediments. Volcanic rocks seem to have almost the same density as sedimentary rocks of the same age.


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

Tanaka HK - Sci Rep (2015)

Average density determined for different rock types.Capital letters indicate rock types: A: accretionary complex formed between 40 and 22 million years ago; B: marine and non-marine sediments formed between 15 and 1.7 million years ago; C: marine and non-marine sediments formed between 1.7 and 0.7 million years ago; D: basaltic and andesitic rock formed between 7 and 1.7 million years ago.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4321185&req=5

f9: Average density determined for different rock types.Capital letters indicate rock types: A: accretionary complex formed between 40 and 22 million years ago; B: marine and non-marine sediments formed between 15 and 1.7 million years ago; C: marine and non-marine sediments formed between 1.7 and 0.7 million years ago; D: basaltic and andesitic rock formed between 7 and 1.7 million years ago.
Mentions: Fig. 9 compares the average densities determined by using data points in different geological domains as indicated with dashed lines in Figs. 4, 5, and 6: (A) accretionary complex formed between 40 and 20 million years ago (2.79 ± 0.05 g/cm3); (B) marine and non-marine sediments formed between 15 and 1.7 million years ago (2.57 ± 0.03 g/cm3); (C) marine and non-marine sediments formed between 1.7 and 0.7 million years ago (2.43 ± 0.05 g/cm3); and (D) basaltic and andesitic rock formed between 7 and 1.7 million years ago (2.51 ± 0.05 g/cm3). The data collected from different regions with identical rock types were merged and averaged to attain better statistics. We can see that as a general trend, the density tends to be higher for older rock, and these values are consistent with gravimetrically determined density values reported by Nawa et al. (1997)3: 2.63 ± 0.09 g/cm3, 2.54 ± 0.15 g/cm3, and 2.58 ± 0.2 g/cm3 respectively for Mesozoic, Tertiary, and Quaternary sedimentary rocks and 2.53 ± 0.15 g/cm3 for Tertiary volcanic rock. As described in the following subsections, the data points located on the fault line were excluded in this plot. Overall, higher density rocks are detected in older geological domains. A closer inspection of Figure 7 reveals an interesting density gap between tertiary and quaternary sediments. Volcanic rocks seem to have almost the same density as sedimentary rocks of the same age.

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.