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.

a_max (m/s²)

Required number in m/s². Peak acceleration.

D_eff (s)

Required number in s. Effective strong-motion duration.

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

Arias intensity proxy I_a ≈ (π/2g)·∫a² dt approximated by PGA² times effective duration. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

I_a (m/s)

Returned number in m/s. Arias intensity.

• 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.
• a_max must be at least 0.
• D_eff 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.

• Directivity Narrowband Pulse Period Calculator

  First-order rupture-duration proxy for directivity pulse period: T_p ≈ L/v_r.

• Housner Spectral Intensity Calculator

  SI(Housner) = integral of PSV over 0.1–2.5 s approximated by trapezoid over supplied spectral velocities.

• Intensity PGA Wald 1999 Table Lookup

  Wald et al. (1999) MMI-to-PGA bounds used in ShakeMap ground-motion to intensity conversion.