Coherence-weighted Wavepath Migration for Teleseismic Data Coherence-weighted Wavepath Migration for Teleseismic Data J. Sheng, G. T. Schuster, K. L. Pankow, J. C. Pechmann, and R. L. Nowack University of Utah Feb. 5, 2004
Motivation Given: Teleseismic data Goal: Local crustal structure Solution I: Receiver function (RF)
Principle of RF (Langston, 1977, 1979) P P PS Moho Vertical Comp. Radial Source history Green’s fun. Instrument
Problems Other phases generate artifacts Other phases generate artifacts Moho pPs pSs pPp
Motivation Given: teleseismic data Goal: local crustal structure Solution I: Receiver function (RF) Solution II: Xcorrelogram mig. (Xmig)
Principle of Xmig GhostP-wave DirectP-wave
Problems Incident angle usually > 30 deg. Incident angle usually > 30 deg. Irregular spacing Irregular spacing Low frequency and long source Low frequency and long source history history
Motivation Given: teleseismic data Goal: local crustal structure Solution I: Receiver function (RF) Solution II: Xcorrelogram mig. (Xmig) Solution III: Coherence-weighted WM
Coherence-weighted WM Outline Synthetic Test Earthquake Data Summary
Coherence-weighted WM Step 1: Calculate radial and vertical RF a. zero-phase traces b. source wavelet c. deconvolution
Coherence-weighted WM Step 2: Migrate RF and obtain ps, pPs, and pPp images Step 1: Calculate radial and vertical RF
Wavepath Migration Plane wave M ps (x)=RRF(T S -T P ) R X’ X X’ X X’ X P S M pPs (x)=RRF(T S +T P ) M pPp (x)=VRF(2T P )
Coherence-weighted WM Step 2: Migrate RF and obtain ps, pPs, and pPp images Step 1: Calculate radial and vertical RF Step 3: Coherence weight
Coherence-weighted WM M CW =W*Mps Depth (km) Distances (km) ps pPs pPp Depth (km) 0220 Distances (km)
Coherence-weighted WM Outline Synthetic Test Earthquake Data Summary
Depth (km) Distances (km) Synthetic Model
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
0 70 Synthetic Seismogram Traveltime (sec.) VerticalRadial
0 20 Radial RF (Synthetic)
0 20 Traveltime (sec.) Vertical RF (Synthetic)
ps Image (Synthetic) Depth (km) Distances (km)
pPs Image (Synthetic) Depth (km) Distances (km)
pPp Image (Synthetic) Depth (km) Distances (km)
CW Image (Synthetic) Depth (km) Distances (km)
Coherence-weighted WM Outline Synthetic Test Earthquake Data Summary
Great Salt Lake Latitude (deg.) Longitude (deg.) Station Map
Processing Parameters Processing Parameters Time (sec.) 50 sec. Passband: 0.2~0.6 Hz Water-level:0.001
Radial RF Time (sec.) Distances (km)
Time (sec.) Distances (km) Vertical RF
Depth (km) Distances (km) ps Image
Depth (km) Distances (km) pPs Image
Depth (km) Distances (km) pPp Image
Depth (km) Distances (km) CW Image
Coherence-weighted WM Outline Synthetic Test Earthquake Data Summary
Summary 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.
Acknowledgment I thank the sponsors of the 2003 UTAM Consortium for their financial support.