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.

φ (°)

Required number in °. Strike azimuth clockwise from north.

δ (°)

Required number in °. Dip from horizontal.

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

Unit normal of a plane from strike/dip in ENU axes: n = (cosφ·sinδ, −sinφ·sinδ, cosδ). Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

n_E

Returned number. East component.

n_N

Returned number. North component.

n_U

Returned number. Up component.

• 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.
• φ must be at least 0.
• φ must be no greater than 360.
• δ must be at least 0.
• δ must be no greater than 90.
• 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.

• Apparent Dip Along Section Line Calculator

  Apparent dip on a section making angle α with the strike: tan(δ_app) = tan(δ)·|sin α|.

• Dipping Refractor True Velocity UpDown Dip Calculator

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

• Double Couple P T Axis Plunge Style Shortcut

  Shortcut P/T axis plunges for ideal focal styles (strike-slip, normal, reverse).