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.

δ (°)

Required number in °. True dip.

α (°)

Required number in °. Angle between section line and strike.

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

Apparent dip on a section making angle α with the strike: tan(δ_app) = tan(δ)·|sin α|. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

δ_app (°)

Returned number in °. Apparent dip seen on the section.

factor

Returned number. Ratio of apparent to true tan-dip.

• 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.
• δ must be at least 0.
• δ must be no greater than 90.
• α must be at least 0.
• α must be no greater than 180.
• 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.

• Strike Dip Plane Normal Vector Converter

  Unit normal of a plane from strike/dip in ENU axes: n = (cosφ·sinδ, −sinφ·sinδ, cosδ).

• Apparent Stress Energy Ratio Calculator

  Apparent stress σ_app = μ · Es / M₀ in megapascals.

• Dipping Refractor True Velocity UpDown Dip Calculator

  True refractor velocity from updip/downdip apparent velocities: V₂ = 2V_uV_d·cosα/(V_u+V_d).