HR: 14:25h
AN: NS33A-04    [Abstracts]
TI: Estimation of Site-Scale Temporal Variations in Seismic Response as a Function of Geophone Placement
AU: Baker, G S
EM: gbaker@utk.edu
AF: Department of Earth and Planetary Sciences, University of Tennessee, 1412 Circle Drive, Knoxville, TN 37996, United States
AU: * Gaines, D P
EM: dgaines1@utk.edu
AF: Department of Earth and Planetary Sciences, University of Tennessee, 1412 Circle Drive, Knoxville, TN 37996, United States
AB: The use of high-resolution geophysical investigations in conjunction with environmental remediation (e.g., separating climate-driven variations from subsurface variations due to anthropogenic manipulations; characterization of infiltration; characterization of subsurface flow and contaminant transport) typically requires temporal resolution not commonly associated with near-surface seismic techniques. Additionally, the estimation of variations in physical and hydraulic properties (i.e., water content; porosity; permeability) using, for example, seismic refraction p-wave velocity tomograms, is controlled by the spatial resolution and signal-to-noise (S/N) of the measured waveform. We therefore investigate the frequency, amplitude, and natural variability of geophone response over time using multiple strategies in geophone placement (e.g., re-coupled on multiple time-scales; buried at varying depths in cylindrical boreholes) in unsaturated unconsolidated fluvial sediments to better define and constrain standard operating procedures for future time-lapse 2D and time-lapse 3D (i.e., 4D) near-surface seismic surveys. In order to delineate natural source variation from subsurface variation, a separate control transect (i.e., geophones were removed and replaced each acquisition period) offset from the static experimental line by 1 meter was acquired simultaneously. Under the assumption the unconsolidated fluvial medium is isotropic at the meter scale, source-receiver positioning is considered identical by locating shots along the median plane of the experimental and control lines. The parallel transects were re-acquired on day, week, and month time-scales coupled with daily climate measurements (i.e., maximum and minimum temperature, precipitation). Of particular interest are periods immediately preceding and following both major and minor climate events that indicate both the rate and effect of climate-driven subsurface recharge.
DE: 1835 Hydrogeophysics
DE: 1895 Instruments and techniques: monitoring
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting