PQC: A novel approach for robust automatic near-surface analysis in low-relief geology

Abstract

A novel approach, named pQC, was developed to automatically derive near-surface velocities and statics by applying surface-consistent analysis to refraction data, where the data consist of first-break (FB) traveltimes and early-arrival waveforms. This approach is facilitated by the introduction of a new sorting domain in which FB traveltimes and traces are organized in a multidimensional space consisting of a common-midpoint (CMP) location, offset, and azimuth, called the XYOA domain. The FB traveltime data sorted in this domain can be analyzed efficiently with statistical methods to obtain localized average depth domain velocity trends for calculation of long-wavelength statics. Short-wavelength (residual) refraction statics are then calculated based on the cross correlation of early-arrival waveforms in the XYOA gathers over multiple offset classes and inverted for surface-consistent source and receiver corrections. The application of the combined statics solution to the traces enhances the continuity and power of the stacked reflected events without the need to perform tomography. Surface-consistent analysis of refraction data in the XYOA domain is fully automatic, provides robust solutions for noisy data, and enhances subsequent reflection residual statics calculations. This method can also be exploited for quality-control analysis of FB picks and for automating, in an iterative procedure, the picking of large 3D seismic data sets. The method is demonstrated on a 3D land survey over complex geology where the novel refraction surface-consistent solution enhances the imaging results and employs a fraction of the time needed by a typical tomographic workflow.