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.

R (km)

Required number in km. Distance from epicenter to the alert site.

V_p (km/s)

Optional number in km/s. P-wave speed.

V_s (km/s)

Optional number in km/s. S-wave speed.

τ_proc (s)

Optional number in s. Detection/processing latency.

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

EEW lead time at a target site: S arrival minus detection epoch (P travel plus processing latency). Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Δt_alert (s)

Returned number in s. Warning time before S-wave shaking.

Late

Returned boolean. Whether shaking precedes the alert.

• 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.
• τ_proc 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.

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