"Shear Wave Velocity Profiling" was the third in a series of Research to Practice Webinars co-produced by the Network for Earthquake Engineering (NEES) and the Earthquake Engineering Research Institute (EERI). The webinar occurred on Wednesday, December 14, 2011 11:30 AM - 1 PM PDT (2:30 PM - 4 PM ET).
It has been increasingly recognized that the shear-wave velocity structure beneath a site is critical in assessing potential site effects on earthquake ground motions. U.S building codes have used the parameter Vs30, the average shear-wave velocity in the top 30 m, for several decades to classify building sites based on the NEHRP site classification system. For more important and critical facilities, shear-wave velocity profiles are needed for site-specific response and hazard analyses. Generally, these Vs profiles are not restricted to the top 30 m but deeper depths are required. Ground motion prediction models such as the Next Generation of Attenuation models are increasingly using Vs30 as an input parameter. Large-scale surveys have also been undertaken to measure the shear-wave velocity profiles at strong motion stations and for developing a range of maps including NEHRP site class maps, site amplification maps, and ground motion hazard maps. Shear-wave velocity can also be used as a means of evaluating liquefaction susceptibility especially for hard-to-sample and border-line soils.
Shear-wave profiling can be performed using a range of techniques including borehole methods such as downhole, suspension and crosshole. Surface-wave methods have become increasingly used because they are nonintrusive, economic and require the least field time. SASW (spectral-analysis-of-surface-waves) and MASW (multi-channel-analysis-of-surface-waves) methods are the two most popular. Ambient-noise methods are also becoming widely used.
In this presentation, Professor Ken Stokoe, University of Texas, Austin and Ivan G. Wong, Principal Seismologist, URS Corporation will discuss the importance of shear-wave velocity profiling in seismic design, its uses, misuses and uncertainties. Case histories will be used to illustrate shear-wave profiling with the SASW method and to show uses of Vs data in a range of seismic design applications.
Credits and References
Professor Ken Stokoe, University of Texas, Austin Ivan G. Wong, Principal Seismologist, URS Corporation
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