If two or more earthquakes occur in the same location and the same source, they will have highly similar waveforms. These "repeating" earthquakes are a common occurrence in glacial, tectonic, and volcanic areas worldwide, and are a useful indicator of seismic activity. Repeating earthquakes can be used to track fluid movement (e.g., water, magma), slip on faults, volcanic activity, or subtle changes in structure, and therefore are a topic of active research in the seismological community. In practice, repeating earthquakes are occasionally noticed visually hours after they occur, but usually go undetected by routine seismic monitoring. Even when noticed, many schemes for detecting repeating earthquakes require manual selection of a template event.

REDPy is an automated system for detecting and cataloging repeating earthquakes at any subset of seismic stations (including a single station), which can be used in near real-time for monitoring or on archived data for research and initial discovery.

For an example of REDPy in action, check out http://assets.pnsn.org/red/ for several instances running on data for the Cascades volcanoes.