HR: 0830h
AN: S41B-08    [Abstracts]
TI: Suppression of Statics and Migration Velocity Errors by Reduced Time Migration of Surface Seismic Data
AU: * Zhou, M
EM: mzhou@mines.utah.edu
AF: Dept. of Geology & Geophysics, University of Utah, WBB717, 135 South 1460 East, Salt Lake City, UT 84112 United States
AU: Yu, J
AF: Dept. of Geology & Geophysics, University of Utah, WBB717, 135 South 1460 East, Salt Lake City, UT 84112 United States
AU: Jiang, Z
AF: Dept. of Geology & Geophysics, University of Utah, WBB717, 135 South 1460 East, Salt Lake City, UT 84112 United States
AU: Schuster, G T
EM: schuster@mines.utah.edu
AF: Dept. of Geology & Geophysics, University of Utah, WBB717, 135 South 1460 East, Salt Lake City, UT 84112 United States
AB: One of the difficulties in seeing beneath salt is that the migration velocity in the salt and above is not well known. This can lead to reduced quality of migration images beneath the salt. There are two ways to remove the kinematic effects caused by the errors in the overburden velocity model: reduced-time migration and interferometric migration. Interferometric migration is very expensive because it extrapolates data from the surface to the reference layer, followed by migration of the extrapolated data to below the reference interface. In comparison, reduced-time migration is as inexpensive as standard Kirchhoff migration because it does not extrapolate the data but rather shifts the data with a time difference between the calculated and natural arrival times of a reference reflection, τ_sg^ref and ~ τ_sg^ref, where s and g denote the source and receiver locations on the surface and τ_sg^ref is calculated by raytracing through the estimated overburden velocity model. This has the effect of removing the error in computing traveltimes in an uncertain overburden model and the statics associated with the shot and receiver. Since the calculated reference reflection times depend on both the overburden velocity model and the depth of the reference layer, a rough estimation of the reference layer depth is usually needed in RTM migration. The reduce-time migration can be implemented in three steps: 1) Pick the natural arrival times ~ τ_sg^ref; 2) shift the data by ~τ_sg^ref; and 3) migrate the shifted data and apply the calculated static shift τ_sg^ref during migration. Test results on synthetic data show the effectiveness of RTM in removing both source/receiver static errors and the timing errors due to an uncertain overburden model above the reference layer. Results with the marine field data show RTM can mitigate the timing error effects associated with the shallow gassy muds.
DE: 0900 EXPLORATION GEOPHYSICS
SC: Seismology [S]
MN: 2005 Joint Assembly