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

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 km2. 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.

Instant snapshot of the internal structure of Unzen lava dome, Japan with airborne muography

“…This technique has been applied to explore the internal structures of volcanoes9101112131415, faults1617, caves181920, carbon capture and storage (CCS)2122, industrial plants23, and historic architecture24. The flux of open-sky vertical muons is ~70 m −2 s −1 sr −1 (ref.…”

Muography

“…Since high-energy muons have a stronger penetration power than X-rays, this technique can create projection images of hectometric to kilometric sized objects. Although there are limitations to the targetable size of the objects that can be imaged by muography, researchers have applied this technique to various scientific targets that include volcanoes [such as Asama, Japan [1][2][3], Satsuma-Iwojima, Japan [4,5], Showa-shinzan, Japan [6], Usu, Japan [7], Unzen, Japan [8], La Sourfiere, France [9,10], Puy de Dome, France [11], Stromboli, Italy [12] and Etna, Italy [13,14]], seismic faults in Japan [15,16], ancient architecture [such as the Egyptian pyramids [17][18][19], and Mt. Echia, Italy [20]], and industrial plants [including electric furnaces [21] and nuclear reactors [22]].…”

Cosmic ray topography

“…3 Cosmic rays have been used for determining the amount of rock overburden on tunnels, imaging of volcanoes, and searching for hidden chambers inside pyramids. [4][5][6][7] In this study, we mapped the topography of the mountain above the Rays Hill tunnel by measuring the cosmic ray flux inside the tunnel. Rays Hill is one of three original Pennsylvania Turnpike tunnels that were abandoned 8 in 1968.…”