HR: 1330h
AN: OS52A-0891    [PDF]
TI: Modeling the Impact of Flood Sedimentation on the Acoustic Response of the Seabed
AU: * Pratson, L
EM: lincoln.pratson@duke.edu
AF: EOS, Duke University, 103 Old Chemistry, Durham, NC 27708 United States
AU: Hutton, E
EM: Eric.Hutton@Colorado.edu
AF: INSTAAR, University of Colorado, 1560 30th St., Boulder, CO 80303 United States
AU: Syvitkski, J
EM: James.Syvitski@Colorado.edu
AF: INSTAAR, University of Colorado, 1560 30th St., Boulder, CO 80303 United States
AU: Kettner, A
EM: Kettner@Colorado.edu
AF: INSTAAR, University of Colorado, 1560 30th St., Boulder, CO 80303 United States
AB: While seldom resolved in seismic reflection data, flood deposits have the potential to modify the seismic response of the seabed offshore of rivers by altering the physical properties of the surface such as grain size distribution, bulk density and porosity. We are assessing the acoustic significance of such changes by simulating the evolution of flood-derived strata offshore of the Po and Pescara Rivers, and the variation in the seabed reflectivity and attenuation of these strata over time. The simulations are being carried out by coupling the sediment discharge model HYDROTREND with the sedimentary-process/stratigraphic model SEDFLUX2D, and the acoustic velocity and attenuation models of Biot and Buckingham. At this writing, only the flood-sedimentation simulations have been completed. Two one-hundred year long simulations have been generated for each river. The Po simulations, which are for the last glacial maximum (LGM) versus the present environment, examine the impact of varying drainage basin area on flood sedimentation (in this case due to differences in sea level). The Pescara simulations are for the pre- and post-emplacement of dams on the river, and address the impact of flow regulation on sedimentation offshore of such rivers. As expected, the simulations for both rivers predict thicker, coarser-grained flood deposits that extend farther offshore of the rivers as their sediment discharge increases. Flood deposits offshore of the Po are predicted to be more substantial during the LGM when lowered sea level increased the drainage basin area of the river to roughly twice its present size. The Pescara simulations suggest that dam emplacement has significantly reduced the coarseness and total amount of sediment being deposited offshore of the river, and that the change is marked by an abrupt upwards transition from coarser, more heterogeneous pre-dam strata to finer, homogeneous post-dam strata. The impacts of these sedimentologic changes on the acoustic character of the seabed are now being modeled.
DE: 3022 Marine sediments--processes and transport
DE: 3025 Marine seismics (0935)
SC: Ocean Sciences [OS]
MN: 2003 Fall Meeting