Abstract
In order to retrieve a 2D background velocity model and to retrieve
the geometry and depth of shallow crustal reflectors in the Southern
Apennines thrust belt a separate inversion of first arrival traveltimes
and reflected waveforms was performed. Data were collected during
an active seismic experiment in 1999 by Enterprise Oil Italiana and
Eni-Agip using a global offset acquisition geometry. A total of 284
on-land shots were recorded by 201 receivers deployed on an 18 km
line oriented SW-NE in the Val D'Agri region (Southern Apennines,
Italy).The two-step procedure allows for the retrieval of a reliable
velocity model by using a non-linear tomographic inversion and reflected
waveform semblance data inversion. The tomographic model shows that
the P wave velocity field varies vertically from approximately 3
km/s to 6 km/s within 4 km from the Earth's surface. Moreover, at
a distance of approximately 11 km along the profile, there is an
abrupt increase in the velocity field. In this zone indeed, an ascent
from 2 km depth to 0 km above sea level of the 5.2 km/s iso-velocity
contour can be noted. The retrieved velocity can be associated with
Plio-Pleistocene clastic deposits outcropping in the basin zone and
with Mesozoic limestone deposits. The inversion of waveform semblance
data shows that a P-to-P reflector is retrieved at a depth of approximately
2 km. This interface is deeper in the north-eastern part of the profile,
where it reaches 3 km depth and can be associated with a limestone
horizon.
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