8 - General Properties of Volcano-Tectonic Earthquake Swarms

Abstract

This chapter discusses the general properties of volcano-tectonic earthquake swarms. It discusses the following characteristics of volcano-tectonic earthquakes: temporal variations in seismic activity, spatial distribution of seismic foci, posteruption seismicity; duration of seismic activity before volcanic event, position of volcanic event in seismic sequence, and dependence of these characteristics on the type of magma feeding the eruption. The temporal variations in seismic activity were of three types: one-peak (I); multi-peak sequences with the maximum peak at the beginning of the sequence (II); or with maximum peak at the end of sequence (III). For basaltic and dacitic volcanoes, the most popular is a seismic sequence with the maximum peak in the beginning of the sequence (Type 2), while for andesitic volcanoes, the maximum number of seismic events for the majority of seismic sequences is observed at the final stage of the swarm. The epicentral area of earthquake swarm is defined as the area of volcano-tectonic earthquake epicenters (magnitude 12 and greater) during eruptive activity. The general cycle of activity of andesitic and dacitic volcanoes may be described by quiescence, phreatic explosive activity with the formation of a new crater, and repeated dome building and destruction accompanied by explosions. It is important to consider the three separate stages during the development of a strategy of alarms when a volcano begins to awake. The first stage is the stage for the monitoring of the awakening process. The second stage is important for understanding that the first explosion of the awakening volcano is not the strongest. The strongest one will occur after some time.