Correlation and Scaling of P and S Anomalies in D" Beneath Central America and Pacific
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Transcript of Correlation and Scaling of P and S Anomalies in D" Beneath Central America and Pacific
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
Rs/p=d(lnVs)/d(lnVp)
Rp/s=d(lnVp)/d(lnVs)
Elastic parameters of MgSiO3 ppv (Wentzcovitch et al. PNAS 2006)
Mineral physics diagram with seismic parameters (Karato and Karki JGR 2001)
Rpho/s
Karason and van der Hilst 200
Tkalcic et al. 2002
Grand 2002
Lay et al. 1998
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)
PKP ray paths
Example seismograms
Sun, Song, Zheng, and Helmberger, PNAS 2007
Sensitivity of PKP differential AB-DF differential times to mantle heterogeneities
Observed PKP residuals plottted at CMB (with Grand’s model)
Azimuthal variation
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
Correlation between observed residuals and predictions
AB-DF vs DF, whole mantle
AB-DF vs AB, whole mantle
AB-DF source side vs station side
Distributions of predicted residauls
P-velocity model of this study
P model at D” and observed residuals
P perturbations along 3 profiles across the Cocos Boundary
along 3 profiles
along latitude
Map of cross-correlation coefficients
PKP data sampling the Pacific from S. America earthquakes to Chinese stations
Zheng, Sun, and Song, Chinese J Geophys 2007
Data and Grand’s predictions
Slope=0.359 +/- 0.040
Grand’s data: ScS residuals plotted at CMB bounce points (distance > 45 deg).
Grand’s ScS-S data and model predictions
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.
Vk2(dVk/Vk)=(Vp
2/R-4/3*Vs2)(dVs/Vs),
where R=Rs/p=(dVs/Vs)/(dVp/Vp)
If R> Vp2/(4/3*Vs
2) or about 2.6 to 2.7 in D”, bulk sound perturbation is anti-correlated with shear wave perturbation.
Work in progress …
ScS-S
SKS-S PKP (AB-DF)