Calculator
Formula used
This calculator uses a constant-velocity travel approximation:
- Travel time:
t = d / v - Distance:
d = v × t - Velocity:
v = d / t
Here, d is path length, v is wave speed, and t is travel time. Real Earth travel times vary with depth, temperature, and ray bending.
How to use this calculator
- Select the calculation mode that matches your known values.
- Enter distance and/or travel time with the correct units.
- Choose a preset wave phase or enter a custom velocity.
- Optional: set an origin time to compute an arrival timestamp.
- Press Calculate to show results above the form.
- Use the CSV or PDF buttons to export your results.
Example data table
| Distance (km) | P-wave (6.0 km/s) time (s) | S-wave (3.5 km/s) time (s) | Surface (3.0 km/s) time (s) |
|---|---|---|---|
| 60 | 10.000 | 17.143 | 20.000 |
| 120 | 20.000 | 34.286 | 40.000 |
| 250 | 41.667 | 71.429 | 83.333 |
Values use the same constant-velocity approximation as the calculator.
Seismic wave travel guide
Seismic wave travel time in context
Seismic travel time is the interval between an earthquake source and a measured arrival at a station. It depends on path length and wave speed through the medium. This calculator estimates that interval for simple scenarios and helps you compare common phases when you need quick, transparent timing for planning.
P, S, and surface waves with typical velocities
Body waves usually arrive first because they move faster through rock. A common classroom starting point is about 6.0 km/s for P-waves and 3.5 km/s for S-waves, while many surface waves cluster near 3.0 km/s. These values can shift with lithology, porosity, temperature, and saturation.
Distance selection and geometry choices
Distance in this tool represents the travel path you want to approximate. For local events, epicentral distance on a map is a practical input. For controlled-source surveys, use shot-to-geophone separation. If you are modeling a straight profile, choose kilometers or meters consistently and document how you measured it.
Model used and what it simplifies
The calculation uses a constant-velocity relation, t = d / v. It treats velocity as uniform along the entire path and ignores ray bending, scattering, and multipathing. That simplification is useful for fast estimates, but real travel-time curves in Earth models vary with depth and lateral structure.
Preset speeds versus custom inputs
Presets are helpful when you need a baseline estimate or a classroom demonstration. Custom velocity is better when you have measured site conditions, such as downhole logging, refraction picks, or laboratory core tests. If you enter km/h or mph, the calculator converts to meters per second internally before solving.
Arrival timestamps using origin time
For travel-time mode, you can optionally provide an origin time to generate an arrival timestamp. This is useful for drills, alerting workflows, or timing comparisons during field exercises. The tool adds the computed travel time to the origin time, rounding to the nearest second for a clean report.
Reading the phase comparison table
When enabled, the comparison table shows how different phase speeds change arrival time for the same distance. Use it to bracket likely arrivals: the P-wave estimate is typically earliest, followed by S and then surface waves. The S–P time gap often grows with distance and can guide quick distance checks.
Practical uses and quick uncertainty checks
Typical uses include estimating first arrival windows, designing sampling buffers for sensors, and sanity-checking picks during processing. To gauge sensitivity, adjust velocity by ±10% and observe how the travel time changes. Record your distance method and velocity source so your results remain interpretable later.
FAQs
1) Which wave preset should I choose?
Choose P for first-arrival estimates in solid rock, S for shear-wave timing, and Surface for near-surface propagation. If you have a site-specific velocity from tomography or lab tests, use the custom option.
2) What distance should I enter?
Use the best path-length approximation you have: epicentral distance, profile length, or instrument separation. Convert map distances carefully and keep units consistent across distance, time, and velocity inputs.
3) Why are P-wave times shorter than S-wave times?
P-waves travel faster because they are compressional waves supported by both solids and fluids. S-waves are shear waves and move more slowly in solids, and they do not propagate through fluids.
4) Does this include refraction through Earth layers?
No. The calculator assumes a constant velocity along a straight path. For layered Earth refraction, curved rays, and phase conversions, use dedicated travel-time tables or full ray-tracing software.
5) Can I compute velocity from observed arrivals?
Yes. Select the velocity mode, enter the distance and the measured travel time, and the tool returns the implied average velocity. Treat it as a path-average value, not a detailed layered profile.
6) How does the origin time field work?
Origin time is optional and only affects travel-time mode. If provided, the calculator adds the computed travel time to that timestamp to produce an estimated arrival time at the station.
7) How do I export results?
After calculating, use the Download CSV or Download PDF buttons in the Results box. Exports include the key outputs, and the PDF also includes the phase comparison table when it is visible.