Title

Determination of Hydraulic Conductivity from SH-Waves

Publication Date

7-2007

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Geophysics

Department

Geosciences

Major Advisor

Paul Michaels

Abstract

A new approach to calculating hydraulic conductivity within an aquifer via inversion of vertical seismic profile (VSP) data is tested in the field and compared to results from standard pumping tests. This approach is accomplished through the mathematical mapping of the damping ratio from the traditional Kelvin-Voigt (KV) model (one spring, mass, and dash pot ) describing soil response, to the Kelvin-Voigt-Maxwell-Biot (KVMB) model (one spring, two masses, and a dashpot positioned between the two masses). The KVMB dashpot describes the viscous damping associated with the relative motion of the sediment or grains in the aquifer (hereafter referred to as frame) and fluid masses. The case with which fluid is able to move independently from the frame, when subjected to seismic waves, is dependent on the permeability of the aquifer, and thus, the hydraulic conductivity.

Seismic data from 18 wells at the Boise Hydrogeophysical Research Site (an unconsolidated fluvial aquifer) are processed and analyzed. A low-velocity layer is identified with focusing of wave energy seen toward the bottom of this layer, producing anomalous damping and damping ratio values. Further processing for determination of hydraulic conductivity must begin in the region below this boundary, where inelastic decay dominates. Hydraulic conductivity values determined with this method range from 0.285 to 1.9 cm/s, with a mean value between all wells of 1.06 cm/s. These values are about one order of magnitude larger than the nonunique solutions determined from the pumping tests. Contour maps are generated from this study, as well as from pumping tests, for comparison of results. Error analysis for the seismic results is performed for a 95% confidence interval.

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