Preliminary shear velocity model from inversion of phase velocity
dispersion measurements from ambient noise cross correlations (440 s)
and twoplane wave analysis of teleseismic earthquakes (20100
s, courtesy of Hersh Gilbert). The SNEP dataset has provided great results in comparison to
others I have analyzed. This is the only dataset where the input
starting model does not have a priori constraints on crustal thickness,
yet upon inversion a Moho gradient is evident that is very sharp on the
east side and less sharp on the west. This is largely due to the
increased resolving power associated with the dense interstation
spacing. PDF files for all images available below. Figure to left is a regional map showing stations and cross section locations. PDF 2.1MB

Crustal thickness map from
velocity gradient analysis. Crustal thickness beneath the Great
Valley is probably selected incorrectly (see leftmost velocity profile
above) so image is clipped at 28 km which is why the Great Valley is
all red. Velocity gradient cross sections obtained here: EW cross sections (PDF, 200Kb) NS cross section (PDF, 200Kb) 
Example of dispersion curve (a) and resulting velocity model after 6 iterations (b). Red circles in (a) show overlapping phase velocity observations from ambient noise and twoplane wave. 
Although the Lcurve analysis of general inverse problems is a heuristic, it provides a quantitative approach to the tradeoffs. As this is an iterated leastsquares problem, the bottom plot below shows that with a few iterations the L2 norm of the residuals decreases rapidly and the solution converges. The upper plot shows the characteristic Lcurve between the L2 norm of the residuals and the L2 norm of model (model energy) for different damping parameters (colorcoded) after 6 iterations for grid nodes in the central Sierras. Two particular damping parameters are noted (0.05 and 0.25). The model with damping of 0.05 is preferred because the resulting model reveals velocity structures and gradients more consistent with prior knowledge, in particular the negative velocity gradients found at about 80 km depth in the Frassetto Pds work and the recent Abt et al. work with Sdp. Also, the mid crustal low velocity region under the north Owens Valley/Long Valley volcanic field is evident. 