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.

τ (s)

Required number in s. Signal duration to coda end.

Δ (km)

Required number in km. Epicentral distance.

a

Optional number. Intercept coefficient.

b

Optional number. Log-duration slope.

c

Optional number. Distance term.

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

Nuttli-style coda-duration magnitude M_d = a + b·log₁₀(τ) + c·Δ with regional coefficients. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

M_d

Returned number. Coda duration magnitude.

• 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.
• τ must be at least 0.
• Δ 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.

• B Value Standard Error Shi Bolt Formula

  Shi & Bolt (1982) b-value uncertainty, simplified for unit-variance magnitude residuals: σ_b = 2.30·b²/√(N−1); supply magnitude residuals for the full Σ(Mᵢ−M̄)² form.

• Felt Radius Heuristic Log Scaling Calculator

  User-parameterized log-linear felt-radius screen R = R₀·10^(kM). The default R₀=0.1 km and k=0.5 are illustrative and must be calibrated for regional attenuation, depth, and reporting conditions.

• Liquefaction Feature Magnitude Bound Lookup

  Ambraseys-style minimum magnitude bound for liquefaction at a given epicentral distance.