Publication Date:
2017-04-04
Description:
We investigate the complex propagation of seismic waves beneath the
Campi Flegrei caldera, Italy, using multichannel recordings of
artificial explosions. The sources consisted of air gun explosions
shot in the Gulf of Pozzuoli at offsets ranging between 3 and 7 km. A
multichannel recording device was deployed in the Solfatara crater and
consisted of ten vertical-component and two three-component
short-period seismometers with a maximum aperture of about 150 m. The
zero-lag correlation (ZLC) technique was adopted to estimate
horizontal slowness and backazimuth of coherent waves crossing the
array. For sources located in the northern sector of the Gulf, with
maximum offset 5 km, ray parameters and backazimuths are in agreement
with those predicted for the 1D velocity model used for routine
locations. For sources at offsets larger than approximately 5 km, the
ZLC curves depict prominent maxima associated with a secondary phase
propagating with a lower velocity than the first-arrival P wave. Using
finite-difference synthetic seismograms generated for a 2D realistic
velocity model, we explain these late arrivals in terms of a lateral
velocity variation located at depths of about 1 km. Such discontinuity
would correspond to a positive V (sub p) anomaly imaged by a recent 3D
tomographic study, and interpreted as the submerged southern rim of
Campi Flegrei caldera collapsed during the explosive eruption of 12 ky
B.P. The small spacing among adjacent shot points allowed simultaneous
wave-field decomposition at the source and receiver arrays. Using a
modified version of the double-beam method, we retrieve the
independent variation of horizontal slowness at both the source and
receiver regions. For both cases, we found azimuthal deviations as
large as 50 degrees with respect to the great circle path. At the
source region, these discrepancies may be interpreted in terms of ray
bending at the interface of the aforementioned positive anomaly. At
the receiver array, the observed anomalies may be attributed to either
velocity variations marking the Solfatara crater rim, or to a
near-receiver, low-velocity body whose position would coincide with
negative gravimetric anomalies and a high V (sub p) /V (sub s) ratio
region inferred by independent geophysical and seismological studies.
Description:
Published
Description:
440-456
Description:
3.6. Fisica del vulcanismo
Description:
JCR Journal
Description:
reserved
Keywords:
tomography
;
campi flegrei
;
wavefield modeling
;
04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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