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.

V₁ (m/s)

Required number in m/s. Upper medium velocity.

V₂ (m/s)

Required number in m/s. Lower medium velocity.

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

Critical angle i_c = arcsin(V₁/V₂); no head wave exists when V₁ ≥ V₂. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

i_c (°)

Returned number in °. Critical angle from vertical.

Possible

Returned boolean. Whether a head wave can be generated.

• 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.
• V₁ must be at least 0.
• V₂ 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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