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.

k

Required number. Productivity constant at t=0.

t (d)

Required number in d. Time since the mainshock.

c (d)

Optional number in d. Omori c offset.

p

Optional number. Decay exponent.

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

Modified Omori law daily aftershock rate n(t) = k/(t+c)^p. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

n(t) (1/d)

Returned number in 1/d. Aftershock rate per day.

N(t,t+1)

Returned number. Expected events over the following day.

• 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.
• k must be at least 0.
• t 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.

• Bath Law Largest Aftershock Gap Note Lookup

  Båth's law: the largest aftershock sits about 1.2 magnitude units below its mainshock.

• ETAS Aftershock Productivity Alpha Calculator

  Relative ETAS-style aftershock productivity 10^[α(M−Mc)]. It omits the fitted productivity constant and Omori time integral, so it is a relative factor rather than an expected event count.

• Aftershock Zone Length Utsu Scaling Calculator

  Utsu aftershock-zone scaling: log₁₀L(km) = 0.5·M − 1.8, with equivalent area.