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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 thickness distribution of the investigated rock overburdens.66% of the investigated tunnels have overburdens thicker than 30 m.
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f2: Average thickness distribution of the investigated rock overburdens.66% of the investigated tunnels have overburdens thicker than 30 m.

Mentions: We chose Miura, South-Boso and South-Izu peninsula as the areas to be imaged through with muons (Fig. 1). Miura peninsula mainly consists of an accreted sediment complex generated 15–20 million years ago on the sea floor of Pacific Ocean20. This complex lifted ~500 thousand years ago and eventually formed what are now Miura and Boso peninsulas. It is known that four active fault segments21 (Kinugasa, Kitatake, Takeyama, and Minami-Shitaura) and two active fault segments (North-Kamogawa and South-Kamogawa) cut Miura and South-Boso peninsulas, respectively22. Izu peninsula, on the other hand, was produced by the collision of submarine volcanoes with Honshu Island one million years ago. These submarine volcanoes were located on the Philippine Sea Plate that was drifting in the direction of Honshu Island. After this collision, these volcanoes uplifted and formed the present shape of the peninsula. Therefore, the Izu peninsula is mainly formed of volcanic rocks20. The sizes of the surveyed areas are 150 km2, 1100 km2, and 90 km2, and the number of observation points are 43, 81, and 22 for Miura, South-Boso and South-Izu peninsula, respectively. Therefore, the average size of the area per observation point is 3.5 km2/point (Miura), 13.6 km2/point (South-Boso), 4.1 km2/point (South-Izu). However, there is a different tunnel distribution in the various sites. The thickness of the surveyed tunnel overburdens ranges from 15 m to 100 m (Fig. 2), depending on the tunnels and the observation altitude is near sea level.


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

Tanaka HK - Sci Rep (2015)

Average thickness distribution of the investigated rock overburdens.66% of the investigated tunnels have overburdens thicker than 30 m.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f2: Average thickness distribution of the investigated rock overburdens.66% of the investigated tunnels have overburdens thicker than 30 m.
Mentions: We chose Miura, South-Boso and South-Izu peninsula as the areas to be imaged through with muons (Fig. 1). Miura peninsula mainly consists of an accreted sediment complex generated 15–20 million years ago on the sea floor of Pacific Ocean20. This complex lifted ~500 thousand years ago and eventually formed what are now Miura and Boso peninsulas. It is known that four active fault segments21 (Kinugasa, Kitatake, Takeyama, and Minami-Shitaura) and two active fault segments (North-Kamogawa and South-Kamogawa) cut Miura and South-Boso peninsulas, respectively22. Izu peninsula, on the other hand, was produced by the collision of submarine volcanoes with Honshu Island one million years ago. These submarine volcanoes were located on the Philippine Sea Plate that was drifting in the direction of Honshu Island. After this collision, these volcanoes uplifted and formed the present shape of the peninsula. Therefore, the Izu peninsula is mainly formed of volcanic rocks20. The sizes of the surveyed areas are 150 km2, 1100 km2, and 90 km2, and the number of observation points are 43, 81, and 22 for Miura, South-Boso and South-Izu peninsula, respectively. Therefore, the average size of the area per observation point is 3.5 km2/point (Miura), 13.6 km2/point (South-Boso), 4.1 km2/point (South-Izu). However, there is a different tunnel distribution in the various sites. The thickness of the surveyed tunnel overburdens ranges from 15 m to 100 m (Fig. 2), depending on the tunnels and the observation altitude is near sea level.

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.