Borehole Muography 1 Purpose p Atmosphere Extension to

Borehole Muography 1

Purpose p Atmosphere Extension to the underground of MUOGRAPHY Target : Fault zone structure　　　　　　 　－position, strike, dip , width, and density μ →Prediction on seismic intensity Typical surface detector cannot measure underground structures because muons only come from the sky How do we measure underground structure? →Put a detector into underground Fault μ Detector There are boreholes near the fault BOREHOLE MUOGRAPHY 2

Development of a new method ＆ detector 1 m Scintillator PMT Zenith Z Muon 1 m ～ 10 cm Only 2 coupled scintillators are used Y X Borehole • Traditional detector 1 m× 1 m →CANNOT be put into the borehole good angular resolution ~ 1° We count when muons come common section ・　New detector 4 cm× 70 cm Angular resolution ~30° Need scanning in boreholes (rotation and up-down) 3 3

Sensitivity of the detector Zenith angle 　　Two factors of sensitivity ・Shape of detector Most sensitive from perpendicular to the detector’s section ・Angular distribution of muons Most of muons come from vertical directions Horizontal muons are absorbed by the ground Muons Borehole Detector Azimuth angle Perpendicular to the section Detector Change angle Change depth Perpendicular to the section Using this detector as a probe, we count muons 4 as a function of depth and azimuthal angle 4

Test observation at Yayoi well (borehole) Does the detector have an ability to measure the density deficit of the low density area(Cavity) ? Well 20 cm ～ 70 m in depth C A D B Yayoi well, located in U Tokyo, was dug by Earthquake Research Institute in 1897. 5

Observation D Period ： March～April, 2013 Points ： Depth=10 m～ 60 m at 10 m intervals 4 directions at 45°intervals 4 directions A C B Time ： about 24 h at each point Rods for directional control 200 cm Interval : 10 m Wire 6 Detector 12 cm 6

Result Does detector know the existence of cavity? Cavity exists in the direction A from well Counting rate A　＞　Counting rate B A B Cavity 0. 3 g/cc Cavity is detected！ Layer 2. 0 g/cc 7

Analysis Result：Density 50 m Estimating density of layers and cavity simultaneously 60° Cavity Layer 2 3. 0 Layer 1 Layer 3 10 m 10 m Layers 2. 5 2. 0 300° 360° 1. 5 360° 1. 0 0. 5 Cavity(60°) 0 0 10 20 30 40 50 60 Using all 24 data points 8

Summary • We developed a new method and a detector to measure the seismic fault zone from boreholes • Test observation at Yayoi well – We measured density deficit • Existence of cavity • Density of cavity and layers 9

Treatment of observation data Data got by observation: Muon＋noise counting rate(/s) → True muon’s counting rate (/s) 　　　　 Process 1　　　　　　Process 2 　 Cut noise by energy loss in the detector revise detection efficiency in 100％ Muon Counts Noise 100％ Pulse height 10

Existence of cavity　→　Density of cavity Layer-Cavity Model ・ ・ 11