Figure 5

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 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. 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, =[], into up-going *P*- and
*S*-wavefield sections, =[], 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.

7/8/2003