Zusammenfassung
A scattering image of the Campi Flegrei caldera has been obtained
using coda wave envelopes from local microearthquake data recorded
at a portable 12-station digital network. This was operated during
the paroxysmic phase of the ground uplift (bradyseism) that occurred
in the years 1983-1984. The Nishigami technique has been used to
obtain the 3D distribution of the strong scatterers in an earth volume
with a horizontal extension of 20 km x 20 km and a vertical thickness
of 6 km. This earth volume was segmented in blocks of 2 km x 2 km
x 2 km for the outer section, and in blocks of 1 km x 1 km x 1 km
for the inner section. The inversion was performed using a hybrid
jackknife-SVD method that has allowed qualitative control of the
stability and robustness of the solution. The results show that the
scatterers revealed by the coda envelopes, which were band-pass filtered
at a center frequency of 18 Hz, match the inner border of the caldera
rim, which is well outlined on land by geological observations. The
scatterer position also delineates this border well beneath sea level.
These results are in close agreement with recently obtained seismic
velocity tomography. The scatterers imaged at the 6 and 12 Hz band-pass
frequencies are located around the zone of maximum uplift, beneath
Solfatara crater, where most of the present residual volcanic activity
is concentrated.
Nutzer