Kansas Geological Survey, Open-file Report 2007-21
by
Richard D. Miller, Brett C. Bennett, Julian Ivanov, Jianghai Xia, Brett A. Wedel, Anthony R. Wedel, and Justin C. Schwarzer
KGS Open-file Report 2007-21
for
Jason McKenna
U.S. Army Engineer Research & Development Center
Geotechnical and Structures Laboratory
Vicksburg, MS 39180
July 2007
Seismic wave propagation at the Yuma Proving Ground (YPG) in Arizona was the focus of a study undertaken with a controlled high frequency vibrator, accelerated impact source, and full wavefield imaging system. The objective of the KGS researchers was to develop an accurate and detailed velocity model in association with an extensive series of sensor tests in an undisturbed portion of the YPG.
During past KGS research activities at YPG, five material-properties (Vp, Vs, Qp, Qs, and density) were estimated based on wavefield measurements and then used to populate cells at subsurface sample points. Properties were assigned throughout the 3-D volume by interpolating 2-D seismic measurements made along survey lines (i.e., subsurface sample points). Surface wave and refraction acquisition methods with customized sources were used to acquire most raw data on previous YPG studies. Data reduction included standard reflection and refraction data analysis procedures as well as turning ray tomography and surface wave analysis methods developed by the KGS for this very unique application at YPG. A variety of seismic energy sources (including vibroseis, accelerated weight drop, and high frequency impulses from projectile and explosive shots) and recording array configurations were evaluated for optimizing the quality of each analysis and in building from those results more focused experiments.
As part of these previous research studies at YPG, inversion of specific portions of the seismic wavefield proved key to the success of the characterization effort. Tomographic inversion produced P-wave velocity matrices with the greatest resolution and finest sampling without the need for assumptions about layer properties. Standard refraction analysis was used to confirm the tomographically defined P-wave velocities and to map prominent layers. Inversion of surface-wave dispersion curves from multichannel data resulted in optimal estimates of the S-wave velocity field. Prior to this study, no numerically rigorous methods had been documented for estimating Q for near-surface materials. Geophysical properties at the site appear to be anisotropic, reflecting local trends in near-surface geology. These studies led to the development of improved signal control systems providing more efficient and focused propagation characteristics.
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Kansas Geological Survey, Geophysics
Placed online May 6, 2008
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