Mainshock‐Aftershock Clustering in Volcanic Regions

Abstract Earthquakes break their general Poissonean behavior through two types of seismic bursts: swarms and mainshock‐aftershock sequences. The former is commonly thought to dominate in volcanic and geothermal regions, but aftershock production, including within swarms, is not well studied in volcanic regions. Here we compare mainshock‐aftershock clustering in active volcanic regions in Japan to nearby nonvolcanic regions. We find that aftershock production is similar in both areas by two separate metrics: (1) Both volcanic and nonvolcanic regions have similar proportions of areas that cluster into mainshock‐aftershock sequences. (2) Volcanic areas with mainshock‐aftershock sequences have aftershock productivity at least as high as nonvolcanic regions. We also find that volcano‐tectonic events that are precursors to an eruption are more common at volcanoes without mainshock‐aftershock clusters than at volcanoes with well‐defined mainshock‐aftershock clusters. This last finding hints at a strategy to identify volcanic systems where cataloged earthquakes are good predictors of behavior.