Processing and inversion of refraction and wide‐angle reflection data from the 1986 Nevada Passcal Experiment

We derive averaged, one‐dimensional velocity models for the crust beneath the Basin and Range in western Nevada by inverting τ(p) composites extracted from slant stacks of refraction and wide‐angle reflection data. A combination of high‐cut filtering in the frequency domain with coherency filtering in the (p,τ) domain has proved effective in smoothing severe static shifts due to lateral heterogeneities and suppressing artifacts due to spatial aliasing. We supplement the low‐frequency information provided by the refraction records with higher‐frequency arrivals picked from the normal incidence and wide‐angle reflection sections. Generalized least squares inversion of data from eight shots for P and S wave velocity structure beneath two perpendicular profiles yields consistent estimates for total crustal thickness (P wave: 30–31 km; S wave: 30–32 km) and average crustal velocity (6.2 km/s; 3.4–3.5 km/s). Average Poisson's ratio beneath the N‐S profile is 0.27–0.28. P wave velocities near the base of the crust (7.4±0.3 km/s) are estimated by inverting precritical reflections from the Moho. Standard errors in depth for these models range from 1 to 3 km; extremal depth bounds, in general, are about twice as large. Uncertainties in velocity, estimated from resolving kernels, range from 0.1 to 0.3 km/s. Estimates of Poisson1s ratio as a function of depth are characterized by large standard errors, reflecting the poor resolution of shear wave velocities. The combination of low average P and S wave velocities with a high average Poisson's ratio in the upper half of the crust, however, is consistent with the presence of fluid‐filled cracks. These results highlight the need for three‐component recording to better resolve shear wave velocity structure.