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

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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

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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

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( , , ) A iT t x x ( , , ) B iT t x x

Ax Bx

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( , , ) ( , , ) ( ) ( )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

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( , )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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VectorSeis sensor maintains dynamic range at extreme low frequencies

LaserVibrometer

Geophone

VectorSeis

Applications

• Persimmon • Basin analysis• Global seismology• Lunar seismology ?