Vent discrimination at Stromboli Volcano, Italy

Abstract

Eruptive activity at Stromboli Volcano was significantly elevated over background levels in May 2001. During 63 h of observation, eight vents produced, on average, 17 explosions/h with an average repose interval of 3 min. During this period, the Stromboli vents exhibited consistent seismic and acoustic signatures, based on cross-correlation cluster analysis. Dendrogram clustering, based on waveform cross-correlation, was used to illustrate the complexity of the near surface plumbing system of Stromboli's multi-vent edifice. Cross-correlations of displacement seismograms produced by explosions at specific craters, such as the Northeast crater (NEC), form dense waveform clusters with correlation coefficients between 0.96 and 0.99, while displacement waveforms from other craters, such as the Southwest crater (SWC), exhibit loose clusters with correlations between 0.88 and 0.96. The inconsistency of SWC events, as compared to the NEC, suggests that the vent system there is more heterogeneous. Cluster linkage distance between the NEC cluster and the Central crater (CC) cluster is shorter than the linkage distance between the NEC and SWC clusters, indicating that NEC and CC are more closely related. Infrasonic observations were used to locate vent explosions confirming that the clusters of events are associated with specific vents or craters. Qualitative analyses of acoustic waveforms from approximately 500 explosions reveal that impulsive acoustic signals were associated with short, mechanically simple ground displacement responses. These events may correspond to the bursting of an individual gas slug. Similar degassing mechanisms from vents in the NEC and the CC show common characteristics in their displacement waveforms.