passive seismic reflection imaging, on the earth and on the moon kees wapenaar delft university of...
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Passive seismic reflection imaging,
on the earth and on the moon
Kees WapenaarDelft University of Technology
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Structural trends in the subsurface of the Netherlands,with recent sources of seismicity (white circles) and contours of constant depth of the Mohorovic discontinuity (Beekman and Stephenson).
25% of antennas in central core
High speed data transport
Antenna cluster (Station)
Central processor
X
Lofar / Persimmon(Permanent Seismic Imaging and Monitoring Network)
Test-site Exloo
Test-site Exloo
Experiments for Experiments for
optimaloptimalreceiverreceiver
responsesresponses
Zoomed-in dynamite Zoomed-in dynamite
recordings at :recordings at :- 12.5 m (left)12.5 m (left)- 6.25m (middle)6.25m (middle)- surface (right)surface (right)
Lofar / Persimmon(Permanent Seismic Imaging and Monitoring Network)
Partners:• Delft University of Technology• Free University of Amsterdam• Utrecht University• TNO-NITG• KNMI• NAM• Shell• MIT
Lofar / Persimmon(Permanent Seismic Imaging and Monitoring Network)
• Delft University of Technology Seismic Interferometric Imaging
Ax Bx
Ax Bx
Cross-correlation
Bx
Ax Bx
ABt
Ax Bx
ABt
ABt
Cross-correlation
Ax Bx
ABtCross-correlation result is equal to impulsive reflection response
Cross-correlation
Bx
Ax Bx
ABt
Ax Bx
ABt
ABt
Simplifying assumptions:
• Direct arrival at xA correlated with primary at xB
• Single diffractor• Primaries only• xA is the specular reflection point
Ax Bx
Ax Bx
ix
( , , ) A iT t x x ( , , ) B iT t x x
Ax Bx
ix
( , , ) ( , , ) ( ) ( )B A B A B AR t R t t x x x x x x
( , , ) ( , , ) A i B ii
T t T t x x x x
( , , )B AR t x x( , , ) A iT t x x ( , , ) B iT t x x
Ax Bx
( , , ) ( , ) ( , )B A obs A obs BR t T t T t x x x x
0 :t
( , , )B AR t x x
1500 m/s
2000 m/s
Ax
( , )obs AT t x
Ax
( , , ) ( , , ) ( , , )B A obs A obs BR t T t T t x x x x x x
AxB Bx x B Bx xAxB Bx x B Bx x
( , )obs BT t x
• Cross-correlation > one virtual source• Repeat for all receivers > many virtual sources• Imaging
Applications
• Persimmon • Basin analysis• Global seismology• Lunar seismology ?
Artist impression of reflection imaging of global seismology data
receiver array
traveltime tomography
Cross-correlation oftransmission responses
source array
reflection imaging
Artist impression of reflection imaging of global seismology data
Applications
• Persimmon • Basin analysis• Global seismology• Lunar seismology ?
Here is a bit of background on the seismology of Moonquakes. The info comes from the book "EARTHQUAKES" by G.A. EIBY the retired superintendant of the New Zealand Seismological Observatory in Wellington city.
Three causes of lunar seismicity:• Impacts• Shallow: 0-60 km (crustal stresses)• Deep : 600 – 900 km (tidal forces)
Features:• ‘High’ frequency (0.1 – 1.0 Hz)• Small amplitudes (0.5 – 1.3 Richter) • Low damping• Long reverberations (~ 60 minutes)
VectorSeis® Digital Sensor
- No tilt limitations
Frequency ResponseGeophone & VectorSeis® simultaneously shaken, table motion measured by Laser
Vibrometer, Geophone and VectorSeis outputs normalized to Vibrometer
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0
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1 10 100
Frequency (Hz)
Am
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esp
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1 10 100Frequency (Hz)
Am
plit
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se in
dB
VectorSeis sensor maintains dynamic range at extreme low frequencies
LaserVibrometer
Geophone
VectorSeis
Applications
• Persimmon • Basin analysis• Global seismology• Lunar seismology ?
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