Magnitude–frequency distribution of volcanic explosion earthquakes

Magnitude–frequency distributions of volcanic explosion earthquakes that are associated with occurrences of vulcanian and strombolian eruptions, or gas burst activity, are examined at six active volcanoes. The magnitude–frequency distribution at Suwanosejima volcano, Japan, shows a power-law distribution, which implies self-similarity in the system, as is often observed in statistical characteristics of tectonic and volcanic earthquakes. On the other hand, the magnitude–frequency distributions at five other volcanoes, Sakurajima and Tokachi-dake in Japan, Semeru and Lokon in Indonesia, and Stromboli in Italy, are well explained by exponential distributions. The statistical features are considered to reflect source size, as characterized by a volcanic conduit or chamber. Earthquake generation processes associated with vulcanian, strombolian and gas burst events are different from those of eruptions ejecting large amounts of pyroclasts, since the magnitude–frequency distribution of the volcanic explosivity index is generally explained by the power law.