HR: 15:45h
AN: NS33A-07    [Abstracts]
TI: Mapping Near Surface Heterogeneities for Geotechnical and Environmental Applications Using Seismic Surface-Waves
AU: * Calderon-Macias, C
EM: cxcalder@hotmail.com
AF: GX Technology, 2101 CityWest Boulevard, Building III, Suite 900, Houston, TX 77042, United States
AU: Luke, B
EM: barbara.luke@unlv.edu
AF: Department of Civil and Environmental Engineering, University of Nevada, Las Vegas, 4505 Maryland Parkway, Las Vegas, NV 89154-4015, United States
AB: Surface wave processing and inversion is a non-destructive method often preferred in near surface studies for estimating shear-wave velocities as a function of depth. In processing, changes in phase as a function of frequency are used to compose single or multi-modal dispersion curves for subsequent interpretation. In multi- channel processing, frequency-wave-number (f-k) or frequency-ray-parameter (f-p) transformations followed by interpretation produces these curves. In single channel-processing, a single dispersion curve is generated by cross-correlating data from receiver pairs at several receiver separations. In either case, phase velocities are inverted through iterative minimization to produce shear-wave velocities as a function of depth. A straightforward extension of the analysis for predicting lateral variations of velocity consists in application of 1D inversion at several locations within some area of interest followed by interpolation in multiple dimensions. Of course this procedure would neglect or treat as noise any wave interaction resulting from lateral heterogeneities due to changes in the elastic properties occurring in the near surface. The scales of the heterogeneities would need to be comparable to those of the recorded wavelengths in order for the data to be sensitive to lateral changes. A possible means to detect the heterogeneities would consist in matching synthetic seismograms computed from a detailed subsurface model with recorded seismic data through waveform inversion. Such a hypothetical inversion would require narrowly constrained parameters at every cell point of a discretized target region as well as a forward modeling method capable of reproducing complex wave propagation phenomena. This procedure is not viable if there is inadequate a priori information to constrain the inversion, and it would be too costly in terms of computation time. An alternative is an interpretative approach that relies on mapping phase and amplitudes from surface wave data to a smooth velocity background model superimposed with local perturbations. The work presented here summarizes inversion of surface wave data in 1D and then discusses the benefits of a staged interpretation procedure for mapping lateral near surface heterogeneities. The proposed methodology has important applications for geotechnical and environmental engineering investigations.
DE: 0560 Numerical solutions (4255)
DE: 0902 Computational methods: seismic
DE: 0910 Data processing
DE: 0935 Seismic methods (3025, 7294)
DE: 3285 Wave propagation (0689, 2487, 4275, 4455, 6934)
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly