HR: 0800h
AN: H21E-1052    [Abstracts]
TI: Partial Derivative Modeling of Shallow Seismic Refraction Tomography Data, Fort Wainwright, Fairbanks, Alaska
AU: * Snyder, C
EM: csnyder@opaliaenv.com
AF: Opalia Environmental, 25 Monroe Place #11F, Brooklyn, NY 11201 United States
AU: Baker, D S
EM: gbaker@geology.buffalo.edu
AF: Department of Geology University at Buffalo, 876 Natural Sciences Complex , Buffalo, NY 14260-3050 United States
AU: Pack, S
EM: skip@dgi.com
AF: Dynamic Graphics, Inc. , 1015 Atlantic Avenue , Alameda, CA 94501-11 United States
AU: Kopczynski, S
EM: Sarah.E.Kopczynski@erdc.usace.army.mil
AF: USA CRREL, 72 Lyme Road, Hanover, NH 03755 United States
AU: Sturtevant, K
EM: ks58@buffalo.edu
AF: Department of Geology University at Buffalo, 876 Natural Sciences Complex , Buffalo, NY 14260-3050 United States
AB: Site characterization studies performed at Fort Wainwright in Fairbanks AK, suggest that contaminant migration in the area is controlled by fracture flow. Shallow seismic refraction tomography surveys were undertaken at this site to further characterize the nature of the bedrock aquifer and to identify structural features that may contribute to groundwater flow and contaminant migration. Two individual surveys were completed; the original survey was conducted in 2002 and during the following field season (2003) a second survey was carried out to address the remaining data gaps. The 2002 and 2003 profiles show the same trends in velocity in areas where they overlap. The similarity of the 2002 and 2003 profiles demonstrates the soundness of both data sets. In addition, several of the prominent seismic features were defined by profiles collected at different orientations (multiple directions) providing further confirmation of data quality. The 2002 and 2003 seismic surveys have different geometries. In 2002, the profiles were 180 meters in length, and, in 2003, they were 300 meters in length. Because of the varying profile lengths and the subsequent change in the number of seismic shots per profile, these data sets have different resolutions. In order to use these data sets together it was necessary to normalize the data. Therefore, partial derivatives (rate of change in velocity per unit of distance) were calculated. The resulting partial derivative profiles highlight differences in the seismic velocity profiles but are not dependent on specific velocity values. These differences are geologic in nature and interpreted to be structural. Differences are referred to as contrast zones and/or lineations. Dynamic Graphic's software EarthVision was used for the partial derivative modeling. Discrete bedrock zones were delineated by the relative contrast in the seismic profiles. Both high and low contrast zones were identified at Birch Hill. The high contrast bedrock zones are defined by several lineations with varying orientation throughout the vertical extent of the profile. The lineations in the high contrast zones were interpreted to be geologic structures, such as fractures and shear zones, which may influence contaminant behavior at the site. Low contrast profiles typically have a single pronounced lateral reflector with minimal variation below and suggest more competent bedrock. The partial derivative models confirm properties suggested by the non-normalized data and allow quantification of the structures.
DE: 8010 Fractures and faults
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting