Correlation and Scaling of P and S Anomalies in D" Beneath Central America and Pacific

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Correlation and Scaling of P and S Anomalies in
D" Beneath Central America and Pacific

• Xiaodong Song
• Department of Geology
• University of Illinois at Urbana-Champaign
• August 7, 2007
• 2nd VLAB Workshop
• University of Minnesota

Collaborators Xinlei Sun, Sihua Zheng, Don
Helmberger, and Steve Grand
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Rs/pd(lnVs)/d(lnVp) Rp/sd(lnVp)/d(lnVs)
Rpho/s
Elastic parameters of MgSiO3 ppv (Wentzcovitch et
al. PNAS 2006)
Mineral physics diagram with seismic parameters
(Karato and Karki JGR 2001)
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Grand 2002
Karason and van der Hilst 200
Tkalcic et al. 2002
Lay et al. 1998
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Direct comparison of P and S tomographic models
is difficult

• Sampling, resolution, and damping are quite
  different.
• S resolution is considerably better. PcP is a
  poor reference phase. PdP is rare.
• P and S correlation becomes poor in lowermost
  mantle (Robertson and Woodhouse 1996 Kennett
  1998 Masters et al. 2000)

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PKP ray paths
Example seismograms
Sun, Song, Zheng, and Helmberger, PNAS 2007
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Sensitivity of PKP differential AB-DF
differential times to mantle heterogeneities
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Observed PKP residuals plottted at CMB (with
Grands model)
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Azimuthal variation
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Event 1 Mar. 15, 2001, 32.32oS, 71.49oW, 37 km,
mb 5.6 Event 2 Sept. 24, 2002, 31.52oS,
69.20oW, 119 km, mb 6.2
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Correlation between observed residuals and
predictions
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Distributions of predicted residauls
AB-DF vs DF, whole mantle
AB-DF vs AB, whole mantle
AB-DF source side vs station side
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P-velocity model of this study
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P model at D and observed residuals
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P perturbations along 3 profiles across the Cocos
Boundary
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along 3 profiles
along latitude
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Map of cross-correlation coefficients
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PKP data sampling the Pacific from S. America
earthquakes to Chinese stations
Zheng, Sun, and Song, Chinese J Geophys 2007
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Slope0.359 /- 0.040
Data and Grands predictions
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Grands data ScS residuals plotted at CMB bounce
points (distance gt 45 deg).
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Grands ScS-S data and model predictions
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Summary Contrary to some previous studies, P and
S perturbations correlate well beneath Central
America and parts of Central Pacific. R values
are significantly different for the two regions.
It is estimated about 1.95 /- 0.09 for Central
America and about 3.30/-0.36 for Central Pacific.
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Vk2(dVk/Vk)(Vp2/R-4/3Vs2)(dVs/Vs), where
RRs/p(dVs/Vs)/(dVp/Vp) If Rgt Vp2/(4/3Vs2) or
about 2.6 to 2.7 in D, bulk sound perturbation
is anti-correlated with shear wave perturbation.
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Work in progress
ScS-S
SKS-S
PKP (AB-DF)