- journal_title：Geophysics
- Contributor：John H. Bradford ; Dale S. Sawyer ; Colin A. Zelt ; John S. Oldow
- Publisher：Society of Exploration Geophysicists
- Date：1998-
- Format：text/html
- Language：en
- Identifier：10.1190/1.1444426
- journal_abbrev：Geophysics
- issn：0016-8033
- volume：63
- issue：4
- firstpage：1248
- section：Articles
We acquired a seismic reflection profile to image a shallow (<100 m) aquifer system on a small island in Puget Sound, north of Seattle, Washington. The aquifer system is comprised of temperate glacial sedimentary strata, with the primary aquifer lying approximately 45 m below the surface. We chose the site because there are water-well boring descriptions available and a sea cliff parallels the profile location, providing stratigraphic control. A 20-lb (9-kg) weight drop was used as an energy source to acquire a 30-fold common-midpoint (CMP) reflection profile along a 400-m line. Analysis of the recorded wavefield was not straightforward because of complex stratigraphy and the presence of a laterally variable thin bed ( approximately 5-15 m) of high-impedance lodgement till within a few meters of the surface. We used finite difference modeling to determine that conventional CMP processing would provide a reasonable approximation for imaging strata in the primary target zone, roughly 20 m below the high velocity till. For CMP processing, we analyzed the velocity structure using iterative dip moveout (DMO) velocity analysis. Use of this method results in a velocity field that dramatically improves the poststack depth-migrated section.