M. Palo

Self-sustained oscillations at Volcán de Colima (México) inferred by Independent Component Analysis

We have analyzed Long-Period (LP) seismic events of Volcán de Colima (Mexico) recorded by four three-component broad-band seismometers during January 2006. Frequency-domain analysis shows spectra mainly peaked in the range 0.3–2 Hz and characterized by a monotonic decreasing envelope, as those produced in a cylindrically-symmetric self-oscillating cavity interacting with a confined jet. Independent Component Analysis, a time-series decomposition method, extracts two or three nonlinear oscillation modes depending on the station, with the fundamental one peaked at 0.4–0.5 Hz. These decomposed waves have a well defined spectral content and are self-sustained oscillations with low dimensionality, as shown by dynamic system reconstruction methods. Moreover, they show radial polarization in near field and transverse polarization in far field in North-West South-East direction. Finally, we hypothesize a branched plumbing system with two principal conduits having alignments orthogonal to one another.

STROMBOLIAN-LIKE VOLCANO ACTIVITY: A COMMON MACROSCOPIC BEHAVIOUR

We report the results of the analysis of the occurrence times of the strombolian-like explosions at Stromboli (Italy) and Erebus volcano (Antarctica). The distribution of the inter-times between successive explosion-quakes is exponential for both volcanoes, the only difference being the occurrence rate. It suggests that the signature of the standard Strombolian activity can be identified in a Poissonian process that rules the mechanism of generation of the explosions. Finally, we adopt coalescence Chandrasekar-Landau mean-field model for the formation of the exploding gas bubbles. The model provides a size distribution that is in a good agreement with the observed bubble dimensions.