Seismic hazard of volcanic activity

Seismic activity is a common feature of volcanic eruptions. The majority of volcanic earthquakes are small; their magnitudes do not exceed 2 or 3. At the same time, significant (moderate size and large) volcanic earthquakes may also occur. The study of 28 significant (Mw≥4.5) earthquakes, associated with volcanic eruptions of 20th century, allowed us to formulate the following results about seismic hazard of volcanic activity: (1) during the 20th century, only three large (Mw≥7.0) earthquakes, directly associated with volcanic eruptions in the world, were recorded. (2) The maximum magnitude Mw was estimated to be 5.4 for earthquakes related to central eruptions, 7.0 for caldera collapse, 5.9 for central eruptions accompanied by flank and (or) fissure eruptions, 7.1 for flank and (or) fissure eruptions without central eruptions, and 5.9 for submarine eruptions. For seismicity just before the eruption, the maximum magnitude of earthquakes was estimated to be Mw=7.1, for seismicity at the initial stage of eruption, Mw=7.0; for paroxysmal stage of eruption, Mw=5.6; and for final stage of eruption, Mw=6.1. (3) It was shown that the recurrence time of eruptions of the same type of volcano associated with significant (Mw≥4.5) earthquakes was more than 100 years for 86% of events studied.