Abstract
We discuss a data-processing sequence adopted to reprocess a seismic
line that crosses the Italian southern Apennines from the Tyrrhenian
Sea to the Adriatic margin and investigate both the overthrust and
foreland areas. We first determine the main causes of the very low
S/N ratio in the field data and then propose a processing sequence
aimed at exploiting the signal content, also making use of a priori
geological knowledge of this area. Our work indicates a combination
of causes for the very low quality of the seismic data. These include
length of the spread (about 20 km) that is unfavorable because of
the rapid variation in the near-surface geology, tectonic complexity,
crooked-line acquisition, and the rough topography associated with
outcropping rocks characterized by highly variable velocities. Based
on the outcome of this data analysis, we present a processing sequence
driven by knowledge of the regional tectonic setting and by knowledge
of the shallow subsurface geology. The main effort is in removing
the large, near-surface related noise components. The low S/N ratio
makes it impossible or nearly impossible to successfully apply highly
sophisticated techniques such as depth migration or wave equation
datuming. Thus, we used robust techniques specifically designed to
solve each problem that degraded data quality. The most relevant
of these techniques were the removal of bad traces where unacceptably
low quality was detected by energy and frequency decay criteria;
estimation and correction for static time shifts attributable to
near-surface conditions; optimization of common midpoint (CMP) sorting
to attenuate the deleterious effects of the crooked-line acquisition;
application of a weighted stacking technique to maximize stack power
and application of prestack f-x deconvolution to attenuate uncorrelated
noise. The outcome of this processing sequence is compared with the
result of a more standard sequence that was previously applied to
the same data and is also discussed in terms of the possible geological
model it might evidence. The realization of a seismic section showing
rather continuous and structured events down to 8 s which, depending
on the interpretation, may be related to Moho discontinuity or to
very deep sedimentary layers supports the efficacy of the processing
approach we propose.
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