Abstract
The joint application of different seismological techniques for seismic
noise analysis, and the results of a volcanological and morphostructural
survey, have allowed us to obtain a detailed and well constrained
image of the shallow crustal structure of the Solfatara volcano (Campi
Flegrei caldera, Italy). Horizontal-to-vertical spectral ratios,
inversion of surface wave dispersion curves and polarization analysis
provided resonance frequencies and peak amplitudes, shear wave velocity
profiles and polarization pattern of coherent ambient noise. These
results, combined in a unique framework, indicate that the volcanic
edifice is characterized by lateral and vertical discontinuities
and heterogeneities in terms of shear wave velocity, lithological
contrasts and structural setting. The interpretation of the seismological
results, with the volcanological and morphostructural constraints,
supports the hypothesis that the volcano has been characterized by
a complex and intense activity, with the alternation of constructive
and destructive phases, during which magmatic and phreatomagmatic
explosions built a complex tuff-cone, later reworked by atmospheric
agents and altered by hydrothermal activity. The differences in the
velocity structure between the central and eastern parts of the crater
have been interpreted as resulting from a possible eastward migration
of the eruptive vent along the deformational features affecting the
area, and to the presence of viscous lava and lithified tuff bodies
within the feeding conduits, which are buried under a covering of
reworked materials of variable thickness. The observed fault and
fracture systems, partially inherited from regional structural setting
and exhumed during volcanism and ground deformation episodes also
seems to strongly control wave propagation, affecting the noise polarization
properties.
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