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.

ΔM12

Required number. Magnitude gap between the two largest events.

T (d)

Required number in d. Sequence duration.

N

Required integer. Total events.

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

Classify a sequence as swarm or mainshock-aftershock from the largest-event dominance and duration. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Type

Returned string. swarm or mainshock-aftershock.

Basis

Returned string. Decision basis.

• 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.
• T must be at least 0.
• N must be at least 1.
• 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.

• Foreshock Mainshock Probable Classifier

  Classify a smaller event as probable foreshock based on its proximity in time and distance to a larger successor.

• 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.