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.