Relationship between soil CO_2 flux and volcanic tremor at Mt. Etna: Implications for magma dynamics

摘要

Large variations of the CO_2 flux through the soil were observed between November 2002 and January 2006 at Mt. Etna volcano. In many cases, the CO_2 flux was strongly influenced by changes in air temperature and atmospheric pressure. A new filtering method was then developed to remove the atmospheric influences on soil CO_2 flux and, at the same time, to highlight the variations strictly related to volcanic activity. Successively, the CO_2 corrected data were quantitatively compared with the spectral amplitude of the volcanic tremor by cross correlation function, cross-wavelet spectrum and wavelet coherence. These analyses suggested that the soil CO_2 flux variations preceded those of volcanic tremor by about 50 days. Given that volcanic tremor is linked to the shallow (a few kilometer) magma dynamics and soil CO_2 flux related to the deeper (～12 km b.s.l.) magma dynamics, the "delayed similarity" between the CO_2 flux and the volcanic tremor amplitude was used to assess the average speed in the magma uprising into the crust, as about 170-260 m per day. Finally, the large amountrnof CO_2 released before the onset of the 2004-2005 eruption indicated a deep ingression of new magma, which might have triggered such an eruption.