Seismic Surface-Wave Tomography of Waste Sites Project ID 55218 Grant # DE- FG07-96ER14706

4/23/00


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Seismic Surface-Wave Tomography of Waste Sites Project ID 55218 Grant # DE- FG07-96ER14706

Leland Timothy Long Georgia Institute of Technology School of Earth and Atmospheric Sciences Atlanta, GA 30332-0340 (404) 894-2860 tim.long@eas.gatech.edu

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Waste dumped on the surface or buried in shallow trenches can contaminate the surrounding rock and soil. The shear-wave velocity is sensitive to changes in soil properties and can be used to map structures that affect containment of the waste. A three dimensional mapping of shear-wave velocity can assist in evaluations of contaminated sites, in addition to locating buried trenches. The sensitivity of shear-wave velocity to fluid content makes it useful for identification of zones of saturated waste fluids and for tracking fluid movement with time. This research demonstrates that it is possible to generate images of shallow shear-wave structure from measurements of surface-wave group-velocity tomography. Images at test sites confirm the presence of anomalous structures.

Why Use Surface Waves

Comparison With Other Methods

Spectral Analysis of Surface Waves (gives depth structure between sensors)

Refraction line. This synthetic example shows the small signal level of P-waves relative to surface waves.

Why Group Velocity

What is Group Velocity

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Why Use Tomography

Ray Geometry and Hit Density

Typical Shot Record

Calculating Group Velocity

Examples of Filtered Traces

Correction for group delays

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Optional Inter-Station Constraint

Tomographic Inversion

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An average dispersion curve and an average structure are found.

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Velocity Structure

Conclusions

Author: Tim Long