A unified method for 2-D and 3-D refraction statics

Abstract

Most of the seismic data processing procedures are divided into 2-D, 2.5-D, crooked lines or 3-D versions dictated by the differences in the shot and receiver configurations. In this paper, we introduce a tomographic approach that overcomes these geometrical difficulties and provides stable statics solutions from picked first-break times. We also show that the first-break picks contain both the short and the long wavelength surface statics. The solutions are obtained by solving a set of generalized surface-consistent delay-time equations using the method of weighted least squares and conjugate gradient. While iterating, each first-break pick is evaluated to ensure its consistency with the least-squares solution. Based on consistency, we weight the traveltime picks and use them in the next iteration. These weights also serve as an indicator of anomalous picks to the user.We show that long wavelength solutions leave large residual errors in the least-squares solutions. We also use the expected length of the Fresnel zone to differentiate between short and long wavelength static solutions. After removing the influence of long wavelength statics, we apply short wavelength statics to reduce the residual errors further.We demonstrate the validity of our unified method by applying it to actual data examples. The removal of both long and short wavelength statics improves the initial data set that produces a more consistent set of velocities and leaves only the short wavelength residual reflection statics, which are generally less than quarter wavelet period delays. This removes the most probable cause of the leg jump contamination and poor velocity estimates from the residual statics computations, especially from the 3-D data.

Joint interpretation of magnetotelluric, seismic, and well-log data in Hontomín (Spain)

“…weathering layer, loose sediments or volcanic stockworks) often produce velocity variations that can affect the arrival time of the energy to the recording geophones, especially in onshore data (Taner et al, 1998;Tryggvason et al, 2009). These areas are usually heterogeneously distributed and commonly feature low propagation velocities.…”

Seismic Reflection Processing for Characterization of a Hazardous Waste Site

“…The refraction statics is computed tomographically (Taner, 1994) with the FOCUS (Cogniseis) software. There are four steps: (1) Pick first arrival times from shot gathers; (2) Assign refractors; (3) Solve for refraction statics; (4) Apply refraction statics correction to data.…”

Shallow velocity–depth model using first arrival traveltime inversion at the CO2SINK site, Ketzin, Germany

“…Therefore, joint interpretation of refraction and reflection seismic data from the near-surface can have many benefits. Numerous sophisticated interpretation techniques of refraction seismic data and tomographic inversion schemes on how to better image the near-surface have been extensively discussed in the geophysical literature (e.g., Hampson and Russell, 1984;Lines and Treitel, 1984;Marsden, 1993;Macrides and Dennis, 1994;Belfer and Landa, 1996;Lanz et al, 1998;Taner et al, 1998;Marti et al, 2002;Bergman et al, 2004). In this study, traveltime inversion techniques based on the generalized linear inversion (GLI) method proposed by Hampson and Russell (1984) have been used.…”