New inferences from spectral seismic energy measurement of a link between regional seismicity and volcanic activity at Mt. Etna, Italy

Vienna (Austria)

EGU

The existence of a relationship between regional seismicity and changes in volcanic activity has been the subject of
several studies in the last years. Generally, activity in basaltic volcanoes such as Villarica (Chile) and Tungurahua
(Ecuador) shows very little changes after the occurrence of regional earthquakes. In a few cases volcanic activity
has changed before the occurrence of regional earthquakes, such as observed at Teide, Tenerife, in 2004 and
2005 (Tárraga et al., 2006). In this paper we explore the possible link between regional seismicity and changes in
volcanic activity at Mt. Etna in 2006 and 2007.
On 24 November, 2006 at 4:37:40 GMT an earthquake of magnitude 4.7 stroke the eastern coast of Sicily. The
epicenter was localized 50 km SE of the south coast of the island, and at about 160 km from the summit craters
of Mt. Etna. The SSEM (Spectral Seismic Energy Measurement) of the seismic signal at stations at 1 km and 6
km from the craters highlights that four hours before this earthquake the energy associated with volcanic tremor
increased, reached a maximum, and finally became steady when the earthquake occurred. Conversely, neither
before nor after the earthquake, the SSEM of stations located between 80 km and 120 km from the epicentre and
outside the volcano edifice showed changes.
On 5 September, 2007 at 21:24:13 GMT an earthquake of magnitude 3.2 and 7.9 km depth stroke the Lipari Island,
at the north of Sicily. About 38 hours before the earthquake occurrence, there was an episode of lava fountain
lasting 20 hours at Etna volcano. The SSEM of the seismic signal recorded during the lava fountain at a station
located at 6 km from the craters highlights changes heralding this earthquake ten hours before its occurrence using
the FFM method (e.g., Voight, 1988; Ortiz et al., 2003).
A change in volcanic activity – with the onset of ash emission and Strombolian explosions – was observed a
couple of hours before the occurrence of the regional earthquakes. It can be interpreted as the magmatic response
to a change of the distribution of tectonic stress in the edifice before the earthquake. In the light of this hypothesis,
we surmise that the magmatic system behaved similar to a dilatometer and promise news lines to forecasting the
volcano activity.

M. Tárraga, R. Carniel, R. Ortiz, J. M. Marrero, and A. García, 2006. On the predictability of volcano.tectonic
events by low frequency seismic noise analysis at Teide-Pico Viejo volcanic complex, Canary Islands. Nat.
Hazards Earth Syst. Sci., 6, 365-376.
Ortiz, R., H. Moreno, A. García, G. Fuentealba, M. Astiz, P. Peña, N. Sánchez, M. Tárraga, 2003. Villarrica
volcano (Chile): characteristics of the volcanic tremor and forecasting of small explosions by means of a material
failure method. J. Volcanol. Geotherm. Res. 128: 247-259.
B. Voight, 1988. A method for prediction of volcanic eruptions. Nature 332, 10:125-130.