Abstract
The Phlegraean Fields are a densely inhabited volcanic area which
includes part of the city of Napoli. During the past 2,000 years
it has been subject to slow vertical movements (bradyseisms). A rapid
uplift was observed in early 1970, which caused alarm in the population.Ground
deformation started to be monitored by means of tide gauge observations
and topographic levelling, making it possible to define the area
interested in the phenomenon and to outline the pattern of deformation.
Vertical deformation data are well fitted by radially symmetric sources,
such as the Mogi's model, while horizontal deformation data are best
fitted by a linear source model.Contemporaneously, a tight seismic
network was installed in the area. The frequency of seismic events
and the released energies have shown that the seismicity of the volcanic
area is very low. Seismic activity evolved both with regard to the
relative occurrence rate of various kinds of shock and to the distribution
of epicentres. The values of the Ishimoto-Iida coefficient, calculated
for three kinds of shock, show that the focal medium is very heterogeneous
down to a depth of a few kilometres. Observations suggest that the
origin of the ground uplift can be attributed to the intrusion of
magmatic masses. This hypothesis is coherent with data and is supported
by structural information.Available data allow a rough estimation
of the maximum magnitude possible for an earthquake with epicenter
in the Phlegraean Fields.
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