Magnitude and Interevent Time Statistics of Strombolian Activity of Villarrica Volcano and Inference Regarding the Flow Regime

Abstract

AbstractThe different flow regimes of two‐phase gas‐in‐liquid flow—as it occurs in the shallow conduit of basaltic volcanoes—are characterized by distinct frequency‐size distributions of the liquid and gaseous slugs. Assuming that the ascent of gaseous bubbles is indicated by seismic events, we explore the possibility of inferring the flow regime from the frequency distributions of magnitudes and interevent times. Our data set consists of 20,000 volcanic seismic events recorded in early March 2012 at Villarrica Volcano (Chile), which are commonly attributed to Strombolian activity. One crucial factor is the completeness of the catalog in terms of detectable amplitudes, which we assess using a stochastic simulation of the network output based on statistical properties of the ambient seismicity. Magnitudes, at which we consider the catalog complete, show an exponential occurrence. Yet, the simulation approach indicates that low magnitude events occur indeed more sparsely than expected for an exponential distribution, and that the magnitude distribution does not obey the Gutenberg‐Richter law. Interevent times are log‐normally distributed, which implies a preferred recurrence interval. The distributions are consistent with a slug flow regime. They correlate weakly with the preceding magnitude, suggesting that slugs coalesce while ascending.