Orthogonal, brick, zigzag, slanted geometries

A land 3D survey is defined by its template: the rule by which shot and receiver lines are laid out relative to each other. Four classical templates cover 90% of modern jobs. Each is a different compromise among three objectives: uniform fold across the image area, uniform azimuth coverage, and crew-roll efficiency.

Orthogonal

Shot lines perpendicular to receiver lines. Simplest to plan; crew-efficient because shot trucks and receiver crews move in orthogonal directions and never interfere. Dominant template since the 1980s. Drawbacks: at small offsets, azimuths cluster around the shot-line and receiver-line directions (0° and 90°) with thin coverage in between; fold is uneven within a template and drops sharply near patch edges. CoV (coefficient of variation in fold across the survey) typically 20–30%.

Brick

Alternate shot rows are shifted by half a shot-line-interval, so shots sit in each other’s fold gaps. The resulting fold map is much flatter (CoV 10–20%), and azimuth distribution improves because neighbouring shot rows no longer fire into the same receivers at the same offsets. Small extra planning cost; same crew productivity as orthogonal. Brick is the default modern land template where neither zigzag efficiency nor slanted azimuth symmetry is critical.

Zigzag

Shot lines meander diagonally between receiver lines, so the shot truck drives a continuous zigzag path rather than stop-start-down-a-straight-line. Designed for continuous vibroseis: the truck never fully stops, sweep cycles overlap with truck movement via slip-sweep, and productivity is the highest of any template (up to 10,000–12,000 VPs/day). Azimuths are broader than orthogonal but fold is less predictable. Used on big desert / open-grassland 3D when crew productivity dominates the economics.

Slanted 45°

Shot lines at 45° to receiver lines. Gives the broadest and most symmetric azimuth distribution of the four — every bin sees a wide rose. Drawback: shot-access roads and receiver-access roads run in different directions, so crew logistics become more involved. Chosen for complex sub-surface where azimuth symmetry is essential (fractured reservoirs, complex faulted overburden).

How to choose

Start with brick as the default. Switch to zigzag if productivity is the dominant cost (big open terrain, long schedule). Switch to slanted if the imaging target has strong dip variability or known azimuthal anisotropy. Stay orthogonal only for small surveys where planning simplicity matters and subtle fold holes are acceptable.

References

• Vermeer, G. J. O. (2002). 3-D Seismic Survey Design. SEG Geophysical References 12.
• Cordsen, A., Galbraith, M., Peirce, J. (2000). Planning Land 3-D Seismic Surveys. SEG Geophysical Developments 9.
• Vermeer, G. J. O. (2012). 3D Seismic Survey Design (2nd ed.). SEG.
• Stone, D. G. (1994). Designing Seismic Surveys in Two and Three Dimensions. SEG Geophysical References 5.