Shallow-to-deep shear wave velocity profiling by surface waves in complex ground for enhanced seismic microzonation of Las Vegas, Nevada

Shear-wave velocity (VS) profiles were developed using the spectral analysis of Rayleigh-type surface waves (SASW) method for 12 sites in the Las Vegas Valley, Nevada, an urban area that is situated on a deep alluvium-filled basin. The objective of the study was to develop VS profiles to depths of 100 m or deeper to support earthquake site response analyses. To that end, a “minivib” Vibroseis was used in conjunction with an instrumented hammer source, allowing development of deep VS profiles, while also maintaining resolution at shallow depths. The results from optimization by linearized inversion compared well with those from simulated annealing followed by linearized inversion. Data from one site known to have a shallow, high-velocity inclusion were analyzed with the benefit of this independent information, which permitted the depth of the inclusion to be estimated closely. Overall, the VS profiles obtained are consistent with an existing earthquake microzonation of the Valley.

► A “minivib” Vibroseis was used with an instrumented hammer to develop detailed shear wave velocity profiles to approximately 100 m depth. ► The new profiles nearly double the number of such detailed and deep VS profiles for Las Vegas Valley, Nevada. ► Optimization was conducted using simulated annealing to create an informed starting model. ► An explicit search for a high velocity layer using simulated annealing successfully resolved its approximate location in the profile. ► New VS profiles are consistent with an existing earthquake microzonation for Las Vegas.