Coherence-weighted Wavepath Migration for Teleseismic Data Coherence-weighted Wavepath Migration for...

Coherence-weighted Wavepath Coherence-weighted Wavepath Migration for Teleseismic Data Migration for Teleseismic Data

J. Sheng, G. T. Schuster, K. L. Pankow, J. Sheng, G. T. Schuster, K. L. Pankow, J. C. Pechmann, and R. L. Nowack J. C. Pechmann, and R. L. Nowack

University of UtahUniversity of Utah

Feb. 5, 2004Feb. 5, 2004

MotivationMotivation

Given: Teleseismic dataGiven: Teleseismic dataGoal: Local crustal structureGoal: Local crustal structure

Solution I: Receiver function (RF)Solution I: Receiver function (RF)

Principle of RFPrinciple of RF

(Langston, 1977, 1979)(Langston, 1977, 1979)

PP

PPPSPS

MohoMoho

P

Ps

Ps

P

G

G

V

R

iGsR

iGsV

Vertical Comp.Vertical Comp.

RadialRadial

Source historySource historyGreen’s fun.Green’s fun.

InstrumentInstrument

ProblemsProblems

• Other phases generate artifactsOther phases generate artifacts

MohoMoho

pPspPs pSspSs pPppPp

MotivationMotivation

Given: teleseismic dataGiven: teleseismic dataGoal: local crustal structureGoal: local crustal structure

Solution I: Receiver function (RF)Solution I: Receiver function (RF)

Solution II: Xcorrelogram mig. (Xmig)Solution II: Xcorrelogram mig. (Xmig)

Principle of XmigPrinciple of Xmig

GhostGhostP-waveP-wave

Direct Direct P-waveP-wave

ProblemsProblems

• Incident angle usually > 30 deg.Incident angle usually > 30 deg.• Irregular spacing Irregular spacing • Low frequency and long source Low frequency and long source historyhistory

MotivationMotivation

Given: teleseismic dataGiven: teleseismic dataGoal: local crustal structureGoal: local crustal structure

Solution I: Receiver function (RF)Solution I: Receiver function (RF)

Solution II: Xcorrelogram mig. (Xmig)Solution II: Xcorrelogram mig. (Xmig)

Solution III: Coherence-weighted WM Solution III: Coherence-weighted WM

Coherence-weighted WMCoherence-weighted WM

OutlineOutline

Synthetic TestSynthetic Test

Earthquake DataEarthquake Data

SummarySummary

Coherence-weighted WM Coherence-weighted WM

Step 1:Step 1: Calculate radial and vertical RFCalculate radial and vertical RF

a.a. zero-phase traces zero-phase traces vvv *

b. source wavelet b. source wavelet vN

s1

c. deconvolution c. deconvolution s

v'

Coherence-weighted WM Coherence-weighted WM

Step 2:Step 2: Migrate RF and obtain Migrate RF and obtain ps, pPs, and pPp imagesps, pPs, and pPp images

Step 1:Step 1: Calculate radial and vertical RFCalculate radial and vertical RF

Wavepath MigrationWavepath Migration

Plane wavePlane wave

MMpsps(x)=RRF(T(x)=RRF(TSS-T-TPP))

RR

X’X’XX

X’X’XX

X’X’XX

PP

SS

MMpPspPs(x)=RRF(T(x)=RRF(TSS+T+TPP))

MMpPppPp(x)=VRF(2T(x)=VRF(2TPP))

Coherence-weighted WM Coherence-weighted WM

Step 2:Step 2: Migrate RF and obtain Migrate RF and obtain ps, pPs, and pPp imagesps, pPs, and pPp images

Step 1:Step 1: Calculate radial and vertical RFCalculate radial and vertical RF

Step 3:Step 3: Coherence weight Coherence weight

Coherence-weighted WM Coherence-weighted WM

MMCWCW=W*Mps=W*Mps

00

606000 220220

Dep

th (

km)

Dep

th (

km)

Distances (km)Distances (km)

psps pPspPs pPppPp

00 220220Distances (km)Distances (km)00 220220Distances (km)Distances (km)

00

6060

Dep

th (

km)

Dep

th (

km)

00 220220Distances (km)Distances (km)

Coherence-weighted WMCoherence-weighted WM

OutlineOutline

Synthetic TestSynthetic Test

Earthquake DataEarthquake Data

SummarySummary

00

606000 220220

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

Synthetic ModelSynthetic Model

Parameters (Synthetic)Parameters (Synthetic)

• Plane P-wave incident at 40 deg.Plane P-wave incident at 40 deg.• 221 Stations with 1km spacing 221 Stations with 1km spacing • Source peak frequency 0.6 Hz Source peak frequency 0.6 Hz

00

7070

Synthetic SeismogramSynthetic SeismogramT

rave

ltim

e (s

ec.)

Tra

velt

ime

(sec

.)

VerticalVertical RadialRadial

00

2020

Tra

velt

ime

(sec

.)T

rave

ltim

e (s

ec.)

Radial RF (Synthetic)Radial RF (Synthetic)

00

2020

Tra

velt

ime

(sec

.)T

rave

ltim

e (s

ec.)

Vertical RF (Synthetic)Vertical RF (Synthetic)

ps Image (Synthetic)ps Image (Synthetic)

00

606000 220220

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

pPs Image (Synthetic)pPs Image (Synthetic)

00

606000 220220

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

pPp Image (Synthetic)pPp Image (Synthetic)

00

606000 220220

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

CW Image (Synthetic)CW Image (Synthetic)

00

606000 220220

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

Coherence-weighted WMCoherence-weighted WM

OutlineOutline

Synthetic TestSynthetic Test

Earthquake DataEarthquake Data

SummarySummary

Earthquake Data Earthquake Data

Great Salt Lake

Great Salt Lake

41.841.8

39.839.8

-113.5-113.5 -110.5-110.5

Lat

itu

de

(deg

.)L

atit

ud

e (d

eg.)

Longitude (deg.)Longitude (deg.)

Station MapStation Map

Processing ParametersProcessing Parameters

120120

5050

270270

200200Tim

e (s

ec.)

Tim

e (s

ec.)

50 sec.50 sec.

50 sec.50 sec.

Passband:Passband:0.2~0.6 Hz0.2~0.6 Hz

Water-level:Water-level:0.0010.001

Radial RF Radial RF

00

202000 200200

Tim

e (s

ec.)

Tim

e (s

ec.)

Distances (km)Distances (km)

00

202000 200200

Tim

e (s

ec.)

Tim

e (s

ec.)

Distances (km)Distances (km)

Vertical RF Vertical RF

00

606000 200200

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

ps Image ps Image

00

606000 200200

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

pPs Image pPs Image

00

606000 200200

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

pPp Image pPp Image

00

606000 200200

Dep

th (

km

)D

epth

(k

m)

Distances (km)Distances (km)

CW Image CW Image

Coherence-weighted WMCoherence-weighted WM

OutlineOutline

Synthetic TestSynthetic Test

Earthquake DataEarthquake Data

SummarySummary

SummarySummary

• ps, pPs, and pPp arrivals in RF can be migrated ps, pPs, and pPp arrivals in RF can be migrated to provide a different perspective. to provide a different perspective.

• CWWM can combine three images to correctly CWWM can combine three images to correctly image the reflector with attenuated artifacts. image the reflector with attenuated artifacts.

• This method can image the Moho at the depth This method can image the Moho at the depth consistent with previous studies. consistent with previous studies.

AcknowledgmentAcknowledgment

I thank the sponsors of the 2003 UTAM I thank the sponsors of the 2003 UTAM Consortium for their financial support . Consortium for their financial support .