Vibroseis deployment in practice

A vibroseis crew is a choreography of trucks, each a 40-tonne shaker, each carrying a steel baseplate lowered hydraulically onto the ground for the duration of a sweep. Multiple trucks work as a group at each VP (Vibrator Point) to boost radiated energy and to randomise phase errors. Productivity is measured in VPs per day, and crew rates range from about 2,000 VPs/day on a small project to 8,000–12,000 VPs/day for a big desert survey with slip-sweep.

The VP cycle

A single VP cycle has five phases: move in (position the trucks at the next VP, ~20–30 s total for the array), deploy (lower baseplates, ~10 s), sweep (synchronised linear sweep 8–16 s, industry sweet spot 12 s), listen (wait for the earth to stop ringing, 2–4 s), and lift (retract baseplates, ~10 s). Classical (non-overlapping) shooting runs end-to-end. With a 12 s sweep, 4 s listen, and 30 s move-up (deploy + drive + lift) the cycle is ≈46 s per VP → ≈78 VPs/hour, or ≈780 VPs per 10-hour day per sail line. Real crews run 2–4 sail lines in parallel — so a 3-line crew reaches ≈2,300 VPs/day classical.

Slip-sweep

Slip-sweep overlaps cycles: the next array begins its sweep while the previous array is still in listen + move-up. Effective cycle per VP becomes max(sweep + listen, move + slip-gap) — whichever phase is the slow one gates the crew. With a 12 s sweep + 4 s listen and a 30 s move-up, classical cycle 46 s collapses to ≈34 s, a ≈26% reduction. With a shorter 20 s move-up the cycle drops to 16 s, ≈65% reduction. Productivity rises from ≈780 VPs/day/line to ≈1,050–2,250 VPs/day/line; a 3-line crew can hit 6,000–9,000 VPs/day on good terrain.

GPS timing and baseplate coupling

Two hardware issues dominate vibroseis data quality. First, the sweep’s time-zero must be known to better than 1 ms at every truck — usually via PPS-disciplined GPS receivers. A 1 ms jitter between trucks means they no longer constructively interfere, wiping ~3 dB off the ground-force output. Second, the baseplate must couple cleanly to the ground. On hard rock or frozen ground the plate may slip, producing harmonic distortion in the radiated signal; on soft alluvium the plate may sink, so that the actual ground force deviates from the pilot sweep by tens of percent. Modern vibroseis electronics (Sercel GPR300, INOVA Aries-II) measure ground force in real time and adjust drive to compensate.

Productivity knobs

At a crew level, a project manager has four knobs: crew size (more trucks → parallel lines), sweep length (longer → better SNR but slower), slip-sweep on/off, and VP spacing. The 2026 standard is 4-truck arrays with 12 s sweeps, slip-sweep on, 50 m VP spacing — about 8,000 VPs/day on open terrain.

References

• Crawford, J. M., Doty, W. E. N., Lee, M. R. (1960). Continuous signal seismograph. Geophysics, 25(1), 95–105.
• Sallas, J. J., Weber, R. M. (1982). Comments on the digital-filter equivalent of a vibrator. Geophysics, 47(11), 1577–1582.
• Pritchett, W. C. (1990). Acquiring Better Seismic Data. Chapman & Hall.
• Cordsen, A., Galbraith, M., Peirce, J. (2000). Planning Land 3-D Seismic Surveys. SEG Geophysical Developments 9.