Frankfort, Kansas

Hubbard, Nebraska

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Ceresco, Nebraska

Milford, Nebraska

Shear Wave Reflection Data

High-resolution shear wave reflection data are collected to provide a detailed image of the subsurface geology between boreholes. Shear wave reflection data are collected rather than the conventional compressional wave data because of the greater resolving power of shear waves. Generally, seismic data can resolve interfaces separated vertically by more than one-quarter wavelength. Because shear waves travel at significantly lower speeds than compressional waves in unconsolidated sediments, the wavelengths are correspondingly shorter for a given signal frequency. 

For a typical survey, a high frequency vibrator sweeping to 200 Hz is used and data are collected on 2 feet group spacing. Often as many as 144 channels are recorded simultaneously resulting in 72 CDP fold data. Shear wave interval velocities in the sediments are 500-1100 ft/s, which results in vertical resolution of less than 2 feet. These data are integrated with VSP, cores, cone penetrometer data, hydrologic models, and chemical analyses to complete the interpretation.

Quick Site^SM:

QuickSite^SM is a methodology to do expedited environmental site characterization in an efficient and cost effective manner. Professionals from various disciplines are brought together to evaluate and conduct research at a site as a team. A component of QuickSite^SM is use of multiple complementary characterization methods and on-site decision making. ESRI's contribution to the QuickSite^SM process is the ability to do in-the-field data processing and interpretation of multifold CDP seismic data. 

The seismic data acquisition is performed by Bay Geophysical Associates, renowned experts in shallow shear wave acquisition. At a field site geologists, geophysicists and geochemists are in the field doing contemporaneous surveys and measurements. As the seismic field crew collects data it is processed and interpreted on powerful laptop computers. Typically, only a half days lag exists between acquisition and production of a brute stack. ANL's cone penetrometer (CPT) truck is in the field with the seismic crew. The CPT has the ability to collect shear wave VSP data to tie borehole measurements to the surface seismic and time-to-depth conversion. Thus, as features are discovered with the seismic data, they are tested with the CPT. All these data are loaded into laptop computers and preliminary interpretations are made in the field.