Detailed Refraction Statics with the GRM & RCS

Abstract

Statics are the corrections to seismic reflection data for the weathered layer and variable topography. Traditional statics routines estimate an initial model of the weathering and then iteratively refine it with NMO velocity analyses and residual statics routines. However, this approach can often be inefficient, especially with the very large volumes of data characteristic of single sensor data, and it has not proven to be especially efficacious with shear wave statics where the low seismic velocities result in quite large traveltimes. By contrast, a new GRM-RCS approach obtains an accurate time model of the weathering which does not require substantial improvement with residual statics. Accuracies of ±1 millisecond can be routinely achieved with good quality data. As a result, the new GRM-RCS approach can improve the efficiency of normal data processing through eliminating at least one iteration of velocity analyses and residual statics. Furthermore, the improved accuracy is necessary where higher frequencies are recorded with single sensor data, if the field statics are to be within half a cycle of the higher dominant frequencies for residual statics routines to be most effective. There can be up to five stages with the GRM-RCS approach. Starting with a new 1D QC algorithm, each stage provides greater resolution of the time model than that obtained in the previous stage. In the final stage, the surface consistent time delays in the surface soil layers are separated from the non-surface consistent time delays originating at the base of the weathering. Because the GRM algorithms are exact and do not require optimization or tomography for accuracy, they can be readily modified to accommodate field data of varying quality, such as with data in which cycle skipping occurs. Furthermore, they can be readily extended to full trace processing with the RCS.