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Synthetic model and data

The idealized lithospheric suture model, shown in Figures [*]a and [*]b, is defined on a 300$\times$120 km$\rm^{2}$ section and consists of three materials with differing elastic properties.

 
Figure4
Figure4
Figure 5
Idealized, three material collisional suture model and representative finite difference data. a) P-velocity model (Velocities and densities of each material are given in Table 2); b) S-velocity model; c) Sample processed synthetic section from model in a) and b) rotated into P wave vector; d) As in c) but rotated SV wavefield.
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A low-velocity crustal layer (white) overlies a faster upper mantle (gray). (See Table 2 in the Appendix A for model velocities and densities). At the location of the suture, crustal material from the lithospheric block to the left bifurcates, with the lower segment descending into the mantle. At a depth of $\sim$40 km, this relict (black) converts to velocities and density higher then the surrounding mantle (note the proportionally greater increase in S-velocity) and thereafter folds and thins to the right of the model.

Several sets of two-component seismograms were computed through the lithospheric model using a 2-D, elastic pseudo-spectral code Kosloff et al. (1990). The seismograms comprise a suite of plane P-wave sources interacting with the model over a range of incident horizontal slowness, p = [0.05, -0.05, 0.06, -0.06, 0.07, -0.07] s km$\rm^{-1}$. The output seismogram sections consist of 120 traces computed at 3km intervals at the free surface.

One preprocessing requirement is that a reasonable zero time mark is computed for all traces. The method employed here consists of transforming raw data sections, $\bf U$=[$U_{\rm 1},U_{\rm 3}$], into up-going P- and S-wavefield sections, $\bf w$=[${\it P,SV}$], via the free-surface transfer matrix Kennett (1991). Multi-channel cross-correlation VanDecar and Crosson (1990) it then applied to a window about the direct P-arrival to allow optimal alignment of wavefield sections. A representative set of synthetics seismograms is presented in Figures [*]c and [*]d. Generally, the two sections are characterized by a combination of spectral sub-planar reflectors, and diffractions from the higher (spatial frequency) wavenumber model structure.


next up previous print clean
Next: Experiments Up: Shragge: Teleseismic PSM Previous: Velocities
Stanford Exploration Project
7/8/2003