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.

Δt (h)

Required number in h. Hours before the larger event.

Δr (km)

Required number in km. Distance to the larger event.

ΔM

Required number. Larger minus smaller magnitude.

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

Classify a smaller event as probable foreshock based on its proximity in time and distance to a larger successor. Inputs are interpreted exactly in the displayed units and the calculation returns the following fields without presentation rounding.

Foreshock?

Returned boolean. Whether the event qualifies as a probable foreshock.

Basis

Returned string. Classification 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.
• Δt must be at least 0.
• Δr must be at least 0.
• ΔM 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.

• Swarm Vs Mainshock Aftershock Sequence Classifier

  Classify a sequence as swarm or mainshock-aftershock from the largest-event dominance and duration.

• Nearest Neighbor Space Time Linkage Distance

  Normalized nearest-neighbor distance for each event against all others.

• Bath Law Largest Aftershock Gap Note Lookup

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