Use this seismology calculation to reproduce a stated convention, screen observations, or compare scenarios whose units, coordinate conventions, catalog selection, and model assumptions are known.

t_p

Required number. P arrival time (epoch seconds).

t_s

Required number. S arrival time (epoch seconds).

R

Required number. Vp/Vs.

The cited overview of Seismometer supplies background for the terminology and domain context used by this tool.^[1]

Origin-time estimate from one station using the Wadati ratio: t₀ = (R·t_p − t_s)/(R − 1). Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

t₀ (s)

Returned number in s. Estimated origin time.

Δt (s)

Returned number in s. S−P interval used.

• Earth structure, source geometry, path effects, site response, instrument response, catalog completeness, uncertainty, and the fitted range can dominate the accuracy of simplified seismic calculations.
• R must be at least 0.
• Use finite inputs in the displayed units, preserve source measurements and assumptions, and independently verify consequential decisions.

For analysis or hazard decisions, retain uncertainty and provenance and compare the result with waveform processing, calibrated regional models, and guidance from qualified seismologists or the responsible agency.

• Spectral Ratio Two Station Q Estimate Calculator

  Two-station coda Q from the log spectral-ratio slope: ln(A₁/A₂) = −π f Δt / Q.

• Characteristic Earthquake Magnitude Window Lookup

  Estimate characteristic magnitude from a fault length using the Wells & Coppersmith strike-slip relation.

• Coda Normalization Lapse Time Amplitude Correction

  Correct coda amplitudes to a reference lapse time using the spreading law A ∝ t^−α.