Features of the volcanic seismicity regime on the example of the eruption of the Icelandic volcano Bárðarbunga in 2015

Volcanic seismicity has quite significant differences from tectonic seismicity, consisting in a different nature: here, instead of the mechanism of accumulation and release of stresses, there is destruction of the rock under the pressure of magma, low-frequency seismic waves arising from vibrations of a large volume of magma, as well as events of an explosive nature, when hot gases rush to the surface. Therefore, the study of the regime of volcanic seismicity is of particular interest. The seismic catalog of Iceland from 1995 to 2019 was analyzed in the study. The seismic regime of the Icelandic volcano Bárðarbunga (BAR) during the eruption is significantly different from the rest of the seismicity of the region. Through detailed reports from the Icelandic meteorological service, it was possible to establish that this difference was mainly due to two processes timed to the eruption: the collapse of the central caldera and the outflow of lava along a fissure swarm. Thus, it was possible to identify the nature of some of the events in the catalog as volcanic. As a result of the analysis of variations of b-value for the process of opening cracks under magma pressure, an anomaly of the b-value known from the literature was revealed, which is typical for so-called volcanic swarms. Thus, evidence was obtained in favor of the hypothesis that such anomalies, often preceding eruptions, are associated exactly with processes of this type. Also, using the Zaliapin– Ben-Zion nearest neighbor method, the grouping of events associated with the eruption was analyzed, and a significantly lower clustering of events was found compared to tectonic regimes, which is probably also due to the difference in the nature of these seismicities.