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.

V_u (m/s)

Required number in m/s. Updip apparent velocity.

V_d (m/s)

Required number in m/s. Downdip apparent velocity.

α (°)

Optional number in °. Refractor dip.

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

True refractor velocity from updip/downdip apparent velocities: V₂ = 2V_uV_d·cosα/(V_u+V_d). Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

V₂ (m/s)

Returned number in m/s. True refractor velocity.

Δ% (%)

Returned number in %. Magnitude of the dip correction.

• 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.
• V_u must be at least 0.
• V_d must be at least 0.
• α must be at least 0.
• α must be no greater than 89.999999.
• 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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