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)