Discriminations between volcanic earthquakes associated with central and lateral eruptions

Abstract

Differences in source radiation are considered for volcanic earthquakes associated with central and lateral (flank) eruptions. P-wave spectra are used to estimate seismic moment, energy class and other source parameters for 16 small Alaid volcano, Kurile Islands, earthquakes associated with the 1972 flank and 1981 central eruptions. Source parameters were studied for both earthquake swarms. Higher M o values are noted for earthquakes associated with the central eruption of the volcano, providing the energy class is equal for earthquakes of both groups. Simultaneously, a relatively higher level of radiation of longitudinal waves is also characteristic. Seismic moment was estimated for 14 relatively large volcanic earthquakes associated with the eruptions of the volcanoes of the world. Seismic moment-surface wave magnitude relations were studied. Higher M o values for earthquakes associated with central eruptions are found. The noted discrepancies in source radiation of the two types of earthquake swarms are accounted for by the different nature of eruptive fractures through which the magma rises during the central and flank eruptions. Eruptive fractures of flank eruptions are characterized by the presence of a number of asperities (barriers) which may cause a higher amount of short-period waves, whereas the eruptive fractures of central eruptions are essentially “smoother”.