11
Borehole Muography 1 Earthquake Research Institute, the University of Tokyo, Japan 2 National Research Institute for Earth Science and Disaster Prevention, Japan 1

Borehole Muography

  • Upload
    gaius

  • View
    52

  • Download
    0

Embed Size (px)

DESCRIPTION

Borehole Muography. 1 Earthquake Research Institute, the University of Tokyo, Japan 2 National Research Institute for Earth Science and Disaster Prevention, Japan. p. Purpose. Atmosphere. μ. μ. Fault. Typical surface detector cannot measure underground structures - PowerPoint PPT Presentation

Citation preview

Page 1: Borehole  Muography

Borehole Muography

1Earthquake Research Institute, the University of Tokyo, Japan2National Research Institute for Earth Science and Disaster Prevention, Japan

1

Page 2: Borehole  Muography

Extension to the underground of MUOGRAPHY

Target : Fault zone structure            

 -position, strike, dip ,width, and density→Prediction on seismic intensity

BOREHOLE MUOGRAPHY

Purpose

2

There are boreholes near the fault

Fault

Detector

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

Atmosphere

p

μμ

Page 3: Borehole  Muography

Development of a new method & detector

• Traditional detector1m×1m×1m→CANNOT be put into the borehole good angular resolution ~ 1°

MuonScintillator

3

1m

1m

~ 10 cm

Borehole

・  New detector4cm×7cm×70cmAngular resolution ~30°Need scanning in boreholes (rotation and up-down)

Zenith Z

X

Y

PMT

Only 2 coupled scintillators are used

7𝑐𝑚We count when muons come common section

3

70𝑐𝑚

4𝑐𝑚

Page 4: Borehole  Muography

Sensitivity of the detector

Detector

4

Zenith angle

Using this detector as a probe, we count muons as a function of depth and azimuthal angle

   Two factors of sensitivity・ Shape of detectorMost sensitive from perpendicular to the detector’s section・ Angular distribution of muonsMost of muons come from vertical directionsHorizontal muons are absorbed by the ground

Perpendicular to the section

36 °

𝒁

𝑿

𝒀

𝒁

𝑿

𝑿

𝒀

Azimuth angle

Detector

4

Muons

Perpendicular to the section

Borehole

Change depth

Change angle

Page 5: Borehole  Muography

Test observation at Yayoi well (borehole)

5

A B

C

D

Does the detector have an ability to measure the density deficit of the low density area(Cavity) ?

20cm

Yayoi well, located in U Tokyo, was dug by Earthquake Research Institute in 1897.

~ 70m in depth

Well

Page 6: Borehole  Muography

Observation

6

Interval : 10m

4 directions

Detector

Period : March ~ April, 2013Points : Depth=10m ~ 60m at 10m intervals4 directions at 45°intervals Time : about 24h at each point

Rods for directional control

Wire

C

AD

B

200cm

12cm6

Page 7: Borehole  Muography

ResultDoes detector know the existence of cavity?

Cavity exists in the direction A from well

Counting rate A  >  Counting rate B

7

Layer2.0g/cc

Cavity0.3g/cc

A

B Cavity is detected!

Depth

Ratio

Page 8: Borehole  Muography

Depth

3.0

2.5

2.0

1.5

1.0

0.5

0

Analysis Result : DensityEstimating density of layers and cavity simultaneously

8

10m

10m

10m

50m

60°

Layers

Cavity(60°)

Cavity

0 10 20 30 40 50 60

Dens

ity )

Layer 2

𝜒2 (𝝆 )=∑𝑖

(𝑁 𝑖❑

𝑐𝑎𝑙 (𝝆 )−𝑁 𝑖❑𝑜𝑏𝑠

√𝑁 𝑖❑𝑜𝑏𝑠

)2

300° 360° 360° 360° 360° 360°

Layer 1

Layer 3

Using all 24 data points

Page 9: Borehole  Muography

Summary

• We developed a new method and a detectorto 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

Page 10: Borehole  Muography

Treatment of observation data

Data got by observation: Muon + noise counting rate(/s)

→ True muon’s counting rate (/s)    

 Process1             Process2 Cut noise by energy loss revise detection efficiency in 100 %in the detector

10

MuonNoise

Coun

ts

Muo

n Ev

ents

)

Depth Pulse height

100%

Page 11: Borehole  Muography

Existence of cavity  →  Density of cavity

11

𝜌𝑐𝑎𝑣𝑖𝑡𝑦

Layer-Cavity Model

𝜒2 (𝝆 )=∑𝑖

(𝑁 𝑖❑

𝑐𝑎𝑙 (𝝆 )−𝑁 𝑖❑𝑜𝑏𝑠

√𝑁 𝑖❑𝑜𝑏𝑠

)2

Observation point according to depth and directionCounting rate (Simulation) in the point under the density model : Counting rate (Observation) in the point

is optimum solution

ρ𝑙𝑎𝑦𝑒𝑟 1ρ𝑙𝑎𝑦𝑒𝑟 2ρ𝑙𝑎𝑦𝑒𝑟 3

・・・