RENEWAL OF SEISMIC ACTIVITY ON KORYAKSKY VOLCANO IN 1994: HYBRID SEISMIC EVENTS AND THEIR USE FOR VOLCANIC HAZARD ASSESSMENT

Abstract

A renewal of seismic activity on Koryaksky Volcano was observed in 1994 since the beginning of detailed seismological observations in 1962. There are no historical descriptions of eruptions on this volcano, except for a weak explosive eruption in 1956-1957. The last period of appreciable activity was dated 3500-7000 B.P., so that the March 1994 earthquake swarm under the volcanic edifice at depths shallower than 8 km may be evidence of the beginning of a new phase in the activity of the Volcano. Among the ordinary volcano-tectonic earthquakes of the Koryaksky swarm, a special type of earthquakes was identified for the first time in the world: distinct signals were recorded prior to P arrivals. The signals had varying durations ranging between a few seconds and a few tens of seconds. Their sources invariably coincided with the hypocenters of the earthquakes that followed. These signals might have been produced by new magma injections into weak zones, the subsequent rupture of which gave rise to normal tectonic earthquakes. These signals may be indicative of magma reactivation under the volcanic edifice and can be used as a reliable tool for estimating further development of volcanic activity.