Deep Shear Wave Velocity Profiling of Poorly Characterized Soils Using the NEES Low-Frequency Vibrator

Surface wave velocity measurements have recently been performed in the Salt Lake Valley region in northern Utah and the Mississippi Embayment region of the Central United States using equipment from the Network for Earthquake Engineering Simulation (NEES) program. A unique, low-frequency servo-hydraulic vibrator (termed Liquidator), developed at the University of Texas at Austin as part of the NEES program, was used to excite the requisite low-frequency energy for these studies. These measurements are the first application of this unique equipment for deep (200 m and greater) shear wave velocity (V_S) profiling of soil sites. This profiling depth was achieved because of the field performance of Liquidator in the 1- to 4-Hz frequency range. Profiles from these studies have contributed to a better understanding of the V_S structure and variability of the deep sediments in these seismically vulnerable regions. The field performance of Liquidator, the shear wave velocity structures, and the importance of such profiles in developing community velocity models for use in earthquake engineering are discussed.