ASA 125th Meeting Ottawa 1993 May

1aAO8. High-resolution shallow water 3-D survey and inversion for geophysical parameters.

Mrinal K. Sen

Paul L. Stoffa

James A. Austin, Jr.

Inst. for Geophys., Univ. of Texas at Austin, 8701 N. MoPac Expwy., Austin, TX 78759

In the shallow water environment even in subsurface depths less than 30 m, 3-D structures can affect wave propagation. A high-resolution (500--3500 Hz) 3-D survey (53 lines; 5-km length, 10-m line spacing, 5-m shot spacing) using a Huntec deep-towed boomer source and STARFIX navigation was carried out offshore New Jersey in 1989. Additional 3-D acquisition along with vibra coring will be conducted in the same region in the summer of 1993. Processing and 3-D interpretation of the data record geologic features hundreds of meters across but only several meters in total depth, i.e., glacial meltwater channels prior to the most recent Wisconsin glaciation. Reducing spatial sampling even to 100-m line spacing results in severe spatial aliasing of these features, making geologic interpretation erroneous. In addition to 3-D structure, local subsurface elastic properties need to be estimated quantitatively by inverse methods. The global optimization methods can be employed to derive earth models and their uncertainties. A major challenge is to combine 3-D acquisition, imaging, interpretation, and core data with the requirements of material property estimation such that a complete understanding of propagation in shallow water environment can be achieved.