HR: 1340h
AN: S33A-1093    [Abstracts]
TI: Adapting Industry Multiple Attenuation Techniques to Crustal-Scale Marine Seismic Surveys
AU: * Gunther, R H
EM: rgunther@lgc.com
AF: Landmark Graphics Corporation, 1805 Shea Center Dr, Ste 400, Highlands Ranch, CO 80129
AU: Levin, S A
EM: salevin@lgc.com
AF: Landmark Graphics Corporation, 1805 Shea Center Dr, Ste 400, Highlands Ranch, CO 80129
AU: Taylor, B L
EM: btaylor@lgc.com
AF: Landmark Graphics Corporation, 1805 Shea Center Dr, Ste 400, Highlands Ranch, CO 80129
AU: Klemperer, S L
EM: sklemp@stanford.edu
AF: Dept. Geophysics, Stanford University, Mitchell, Room 360, 397 Panama Mall, Stanford, CA 94305
AU: Goodliffe, A M
EM: amg@ua.edu
AF: Geological Sciences, University of Alabama, 202 Bevill Building, Tuscaloosa, AL 35487
AU: Oakley, A J
EM: aoakley@hawaii.edu
AF: SOEST, University of Hawaii, 1680 East-West Road, POST 802, Honolulu, HI 96822
AU: Taylor, B
EM: taylorb@hawaii.edu
AF: SOEST, University of Hawaii, 1680 East-West Road, POST 802, Honolulu, HI 96822
AB: Academic marine seismic surveys often focus on crustal targets situated in areas with deep water and rough topography. Thinly-sedimented seafloor creates strong and late-arriving water-column reverberations, often termed multiples, that can completely obscure deeper primary reflections. In a 2002 survey of the Mariana back-arc, arc, and fore-arc regions, large topographic variations produced strong multiples which were not significantly attenuated by stacking or migration. Using swath bathymetry, collected by the onboard multi-beam sonar system, we adapt industry multiple attenuation tools to extract useable data from below the water-bottom multiple. Standard approaches to multiple removal either take advantage of differences in move-out velocities between primary and multiple arrivals in order to filter out multiples or attempt to model multiples so that they can be adaptively subtracted from the data. Until recently, most modeling tools were restricted to 2D but still performed effectively against the well-behaved multiples often encountered in commercially important areas. But these algorithms have limited effectiveness against multiples generated from 3D structures such as salt domes, so the petroleum industry has recently made a strong push for 3D algorithms. In academic surveys, out-of-plane effects are all-too-often too large for successful application of 2D models, but due to the large regions of interest and budget constraints, 3D surveys are typically out of reach. Surface-Related Multiple Elimination (SRME) is a powerful approach that predicts multiples that reflect at least once off the free surface and can model any multiples that bounce off the surface along the source-receiver line. Developed from 1D theory laid down in the late `70s at Stanford University and extended to 2D in the `80s by Delft University, it has become widely used in commercial hydrocarbon exploration. The version of SRME we adapt to the Marianas survey convolves field shot gathers with synthetics constructed from picked horizons. For us, its advantage over pure SRME is that there is more control over which multiples should be predicted and how they are modeled. In particular, the approach allows us extra flexibility to model out-of-plane multiples. To help adapt this process to the rough topography of the Mariana subduction zone, we use swath bathymetry to allow the hybrid SRME to construct synthetic shot records with out-of-plane as well as in-plane reflections. We also model multiples of the seafloor reflection itself directly using Kirchhoff summation over all possible ray-paths. This latter tool only predicts first-order multiples from the seafloor, but unlike SRME, is not inherently limited by the source-receiver data recording geometry. Finally, we use the relationship between the predicted and actual multiple arrivals to extract information about cross-dips, i.e. out-of-plane, effects.
DE: 3025 Marine seismics (0935)
DE: 0900 EXPLORATION GEOPHYSICS
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting