Time-space variation of volcano-seismic events at La Fossa (Vulcano, Aeolian Islands, Italy): new insights into seismic sources in a hydrothermal system

Abstract

We investigated the relationship between volcano-seismic events, recorded at La Fossa crater of Vulcano (Aeolian Islands, Italy) during [2004][2005][2006], and the dynamics of the hydrothermal system. During the period of study, three episodes of increasing numbers of volcano-seismic events took place at the same time as geothermal and geochemical anomalies were observed. These geothermal and geochemical anomalies have been interpreted as resulting from an increasing deep magmatic component of the hydrothermal fluids. Three classes of seismic events (long period, high frequency and monochromatic events), characterised by different spectral content and various similarity of the waveforms, have been recognised. These events, clustered mainly below La Fossa crater area at depths of 0.5-1.1 km b.s.l., were space-distributed according to the classes. Based on their features, we can infer that such events at Vulcano are related to two different source mechanisms: (1) fracturing processes of rocks and (2) resonance of cracks (or conduits) filled with hydrothermal fluid. In the light of these source mechanisms, the increase in the number of events, at the same time as geochemical and geothermal anomalies were observed, was interpreted as the result of an increasing magmatic component of the hydrothermal fluids, implying an increase of their flux. Indeed, such variation caused an increase of both the pore pressure within the rocks of the volcanic system and the amount of ascending fluids. Increased pore pressures gave rise to fracturing processes, while the increased fluid flux favoured resonance and vibration processes in cracks and conduits. Finally, a gradual temporal variation of the waveform of the hybrid events (one of the subclasses of long period events) was observed, likely caused by heating and drying of the hydrothermal system.

Multiparametric Approach in Investigating Volcano-Hydrothermal Systems: the Case Study of Vulcano (Aeolian Islands, Italy)

“…In all these cases, the inferred source mechanism was suggested to be the resonant excitation of cracks/conduits filled with fluids. Finally, other seismic events with very long duration (30-50 s) and sharp spectral peaks above 5 Hz are recorded at Vulcano and can be referred to as tornillos (hereafter referred to as TR; ALPARONE et al, 2010;MILLUZZO et al, 2010), since they show a similar long duration to the tornillos recorded at other volcanoes (e.g., Galeras, GOMEZ and TORRES, 1997;Tongariro, HAGERTY and BENITES, 2003). Hereafter, with the term volcano-seismic events we refer indistinctly to all the above described seismic events with the exception of VT earthquakes.…”

“…They occur at the same time as increases in the number of volcano-seismic events (GRANIERI et al, 2006;INGUAGGIATO et al, 2008;ALPARONE et al, 2010). During the last century, several temperature and geochemical anomalies occurred at La Fossa that were not followed by eruptions: 1916eruptions: -1924eruptions: , 1977eruptions: -1993eruptions: , 1996eruptions: (ITALIANO et al, 1998CAPAS-SO et al, 1999;DILIBERTO et al, 2002;CARAPEZZA and GRANIERI, 2004).…”

Multi-parametric investigation of the volcano-hydrothermal system at Tatun Volcano Group, Northern Taiwan

“…As the Sompi method also calculates amplitudes of the wave elements, we have added this information to the frequency-growth diagram by using a color scale. This additional parameter can help constrain better the values of Q since high-amplitude clustered wave elements are considered dominant spectral components of the LF signal, while low-amplitude scattered wave elements represent most likely noise (Alparone et al, 2010). Figure 9 shows two of the three LF event waveforms that were analyzed, their Fourier amplitude spectrum and the results of the Sompi analysis.…”

Learning about Hydrothermal Volcanic Activity by Modeling Induced Geophysical Changes

“…An active hydrothermal system has been detected beneath La Fossa Caldera, developed as a consequence of different collapse events between 80-8 ka (De Astis et al, 2013). Gravity, seismological, and geochemical studies (Chiodini et al, 1992;Berrino, 2000;Alparone et al, 2010) place the active hydrothermal system at a depth between 500 and 1500 m below sea level. At present, its activity is represented by fumarolic emissions located within the crater, where a few high temperature zones are active (De Astis et al, 2003) on the southern and northern flanks of the edifice and in the eastern part of the island (baia di Levante).…”

“…The shallow structures of volcano complex were defined by several geophysical studies since the 70s (Barberi et al, 1994;BlancoMontenegro et al, 2007;Napoli and Currenti, 2016;Ruch et al, 2016), and by two deep geothermal drillings (Figure 1) in 1983-1987(Gioncada and Sbrana, 1991, located at the foot of the south-western and northern flanks of La Fossa crater. Since the end of the last magmatic eruption in 1890, the volcano activity has been characterized by fumarolic emissions of variable intensity and temperature and seismic crises due to magmawater interaction (Alparone et al, 2010;Federico et al, 2010). An active hydrothermal system has been detected beneath La Fossa Caldera, developed as a consequence of different collapse events between 80-8 ka (De Astis et al, 2013).…”