Abstract
The Campi Flegrei located west of the city of Naples, is one of the
most active calderas in the world. With several hundred thousand
people living within its borders, this area is considered at high
risk for eruptive scenarios. With the aim of investigating and reconstructing
the volcanic structure of the Campi Flegrei caldera, the extensive
marine investigation SERAPIS was carried out in the area in September
2001. The large amount of data provided by the experiment is still
able to provide new insights into the velocity structure underneath
the Campi Flegrei area. This study discusses a 3D velocity model
with seismic interfaces for the Campi Flegrei caldera from the joint
inversion of first and secondary seismic phases based on the SERAPIS
dataset. The traveltimes used during the inversion are obtained by
a refined manual picking of first arrivals and of main reflected/converted
(PP and PS) phases. The dataset of first arrivals is the same as
used during the previous tomographic studies of the area, but the
travetimes have been manually re-picked. Concerning the reflected
dataset, we performed a refined picking of the main PP and PS reflections
on vertical and radial seismic sections composed with traces arranged
in 3D Common Mid Point gathers. Three main reflection events have
been inferred through graphic display of the seismic sections and
analysis of the lateral coherency of reflection events by visual
comparisons of different gathers along EW and NS profiles. Preliminary
information on the morphology of reflectors has been obtained using
the residual traveltimes between observed reflected picks and reflected
traveltimes computed for 1D interfaces and using an average 1D velocity
model with the aim of indicating large wavelength anomalies of the
reflector depths. A final joint inversion has then been applied for
the determination of the morphology of the reflector using CAT3D
software which models both the velocity in the bulk and the shapes
of the layers. Moreover, the joint use of first arrivals and reflected/converted
data investigates the extension of a new 3D velocity model at greater
depths as compared to tomographic models based on the inversion of
only first arrival traveltimes.
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