S.R. McNutt J.P. Benoit 1996 <p>Earthquake swarms are pervasive at volcanoes, but have seldom been studied systematically. Most swarms that are described in the literature are those that occurred in association with eruptions; indeed, earthquake swarms are the most reliable method of forecasting eruptions. For the purpose of this report, a swarm is defined as many earthquakes of the same size occurring in a small volume. Swarms are different in these two ways from a mainshock-aftershock sequence or a foreshock-mainshock-aftershock sequence (fig. 1). Swarms are especially common in volcanic areas</p> application/pdf 10.3133/ofr9669 en U.S. Geological Survey Global volcanic earthquake swarm database 1979-1989 reports