Volcanic tremor location during the 2004 Mount Etna lava effusion

A lava emission started at Mt. Etna, Italy, on 7
September, 2004. Neither earthquake seismicity heralded or
accompanied the opening of the fracture field from which
the lava poured out, nor volcanic tremor changed in
amplitude and frequency content at the onset of the
effusive activity. To highlight long-term changes, we
propose a method for the location of the tremor source
based on a 3D grid search, using the amplitude decay of the
seismic signal, from January to November 2004. We find
the centroid of the tremor source within a zone close to and
partially overlapped with the summit craters (pre-effusive
phase), which extended up to 2 km south of them (effusive
phase). The depths are of between 1698 and 2387 m a.s.l.
We hypothesize the lava effusion stemmed from a degassed
magma body, although we find evidence of temporary
magma overpressure conditions, such as those documented
on 25 September.

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