Seismic Travel Time Calculator

Formula used

• Direct (straight ray): t = x / V
• Direct with takeoff angle (from vertical): L = x / sin(i), then t = L / V
• Reflection to a flat interface (symmetric): t = 2 * sqrt(h^2 + (x/2)^2) / V1
• Two-layer head wave (critical refraction): sin(ic) = V1 / V2, t0 = 2 h cos(ic) / V1, t = t0 + x / V2

Assumptions: horizontal layers, constant velocities in each layer, and a single planar interface.

How to use this calculator

1. Pick a computation mode that matches your experiment.
2. Enter the source-receiver distance and select its units.
3. Provide the upper-layer velocity V1 in your chosen units.
4. For reflection or two-layer cases, enter interface depth h.
5. For two-layer refraction, also enter V2 where V2 exceeds V1.
6. Optionally enable takeoff angle to adjust direct-ray path.
7. Press Calculate to display times above the form.
8. Download CSV or PDF to archive the computed values.

Professional notes

In refraction surveys, the refracted arrival can become first at larger offsets. Compare direct and refracted times to estimate crossovers, then validate with observed picks.

For near-surface work, use realistic S-wave velocities (often 150–800 m/s) and consider strong heterogeneity. This tool intentionally keeps the physics transparent for quick checks.

Accurate travel times improve picks, inversions, and interpretations greatly.