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TitleEvaluation of shear-wave velocity profiles from ambient vibration array recordings in SW British Columbia, Canada
AuthorMolnar, S; Ventura, C E; Finn, W D L; Taiebat, M; Dosso, S E; Cassidy, J F
SourceProceedings of the 15th World Conference on Earthquake Engineering; 2012 p. 1-10
Alt SeriesEarth Sciences Sector, Contribution Series 20120123
Meeting15th World Conference on Earthquake Engineering; Lisbon; PT; September 24-28, 2012
ProvinceBritish Columbia
AreaFraser River Delta
Lat/Long WENS-123.5000 -123.0000 49.2500 49.0000
Subjectsgeophysics; seismic velocities; velocity surveys; earthquakes; earthquake mechanisms; earthquake studies; strong motion seismology
Illustrationslocation maps; graphs; plots
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
Current practice to predict amplification of earthquake motion due to the 1D sedimentary layering at a site is based primarily on the shear-wave velocity (VS)-depth profile. Hence, cost-effective urban field techniques to measure and/or estimate VS of the subsurface are of great interest to the earthquake engineering community. The microtremor array method involves recording ambient vibrations with an array of seismic sensors to extract phase velocity surface wave dispersion data which can be inverted for the VS structure at a site. A variety of sediment sites in SW British Columbia, Canada, collocated with invasive VS measurements (downhole and seismic cone penetration) and/or locations of earthquake recordings, have been chosen to assess performance of this passive-source seismic method in providing VS profiles applicable for site response characterization. This paper presents the process of determining and evaluating acceptable VS models at a site. A best-fit VS profile is determined from inversion of ambient vibration array recordings, for a given model parameterization, using a hybrid optimization scheme. The most appropriate model parameterization is determined using the Bayesian information criterion, which provides the simplest model consistent with the resolving power of the data. Parameterizations considered vary in the number of layers, and include layers with constant, linear and power-law gradients. The best-fit VS profiles are assessed for reliability by direct comparison with collocated invasive VS measurements. Overall, fair to excellent agreement is obtained between invasive VS measurements and the best-fit VS profile for the three sites investigated here. These results provide confidence that sufficient detail of the VS profile is derived via inversion of microtremor dispersion data for site response characterization.