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Titel |
Imaging the intrusion of a magmatic sill beneath the town of Pozzuoli (2012-2013) |
VerfasserIn |
Luca D'Auria, Susi Pepe, Raffaele Castaldo, Flora Giudicepietro, Giovanni Macedonio, Francesco Casu, Riccardo Lanari, Mariarosaria Manzo, Eugenio Sansosti, Ivana Zinno, Pietro Tizzani |
Konferenz |
EGU General Assembly 2015
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 17 (2015) |
Datensatznummer |
250105400
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Publikation (Nr.) |
EGU/EGU2015-4920.pdf |
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Zusammenfassung |
Campi Flegrei caldera (Southern Italy) is among the areas with the highest volcanic risk in
the world. The megacity of Naples, hosting more than 1 million inhabitants, lies across the
caldera borders. In recent years Campi Flegrei caldera has experienced an accelerating uplift
rate of the ground deformation. In particular, during the April 2012 - January 2013 time
interval the caldera has shown a rapid uplift of about 6 cm with a peak rate of about 3
cm/month in December 2012. This event led the Italian Civil Protection to raise the alert level
of the volcano from green to yellow. We exploited the displacement time series
obtained by processing 90 SAR images acquired from the COSMO-SkyMed sensor
constellation along ascending orbits via the well-known DInSAR algorithm referred to as
SBAS algorithm, and the measurements provided by 14 continuous GPS stations
deployed within the caldera and belonging to the permanent INGV-OV monitoring
network. To study the detail of the intrusion process we have applied novel geodetic
imaging technique to determine the spatial and temporal kinematics of the ground
deformation source in the selected period. The retrieved temporal pattern of the source
geometry reflects that of a growing sill which, at the end of the considered period, has a
roughly elliptical geometry with an extension of about 6 km in the EW direction and
about 4 km in the NS one. The maximum aperture of the sill is of about 30 cm
at its center. To understand the dynamics of this phenomenon we used a recently
developed numerical model of the emplacement of a magmatic sill, to fit the retrieved
geometry. The parameters to be determined are: the average magma viscosity, the
amount of magma already present in the sill before the 2012-2013 episode and the
magma injection rate. Results show that the most likely value for the viscosity is
between 103 - 104Pa /
s and that to justify the observed deformation pattern it is
required that the reservoir should have contained at least 1010kg of liquid magma
before 2012. The injection rate has two main peaks on September and December
2012, and a smaller one on March 2013. The first two peaks have a value of about
400 kg/s and duration of 3-4 months. The total amount of injected magma is of
about 8.2 /
1010kg. The magma viscosity value is compatible with that of the most
common magmas erupted in the past 40 ky: phonolites, while the total inferred
amount of liquid magma is of the same order of magnitude of small-size eruptions
(VEI 2-3) occurred in the caldera during the last 15 ky. The first injection peak is
associated with a seismic swarm, located beneath the town of Pozzuoli. The swarm
consisted in about 200 earthquakes (maximum magnitude 1.8) occurring within an
interval of about 1.5 hours. The hypocenters were located outside the area usually
affected by microearthquakes in the previous years. Using finite element structural
mechanical modeling we show that the inferred source caused a marked increase in the
maximum shear stress along the rim of the sill. In fact hypocenters were located very
close to the northern edge of the growing magmatic reservoir. Our findings suggest
a key to interpret the caldera unrest that, started about 60 years ago, has led to a
maximum uplift in the area of more than 3 m. Consequently, the observed uplift
phenomenon could be interpreted in terms of injection of limited magma batches
feeding the growth of a shallow magmatic reservoir. Similar mechanisms have
been inferred for other calderas, where the repeated emplacement of magmatic
sills has been recognized having an important role in the evolution of the volcano.
Accordingly, the observation of short evolution of volcanic precursory phenomena
as well as the development of innovative real-time analysis techniques should be
taken into account for an effective surveillance of the Campi Flegrei caldera. This
work has been supported by the Italian Department of Civil Protection and by the
Italian Space Agency under theSAR4Volcanoes project (agreement n. I/034/11/0)
and by MED-SUV project (European Union’s Seventh Programme for research,
technological development and demonstration under grant agreement No 308665). |
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