Geophysical data acquisition - OGS

allow for the different spatial sampling in the in-line and cross-line directions.
Results from the St. Austell Bay survey showed that the methodology worked well.
3-D stack cubes using a one metre bin size were produced on datasets from both
the acquisition systems. The complex channeling in the area was well delineated
with a vertical resolution of less than half a metre. A presentation on this 3D
methodology has been accepted for the 63rd Annual Meeting of the EAGE in
Amsterdam in June 2001.
The group was also involved in a research project, funded by ENI (Agip Division)
through the University of Parma to study crustal movements and the processes of
convergence and sedimentation in the Eastern Mediterranean. Within the project,
1000 kms of seismic data, recorded by OGS in the seventies, was reprocessed and
interpreted in order to design scaled physical models for sediment deformation
experiments in the laboratory. This physical modelling was performed by a team
from the University of Parma (Department of Earth Sciences) and IGN-CNR
Bologna. The reprocessed data crossed the eastern Mediterranean ridge
accretionary complex and extended to the Herodotus foredeep and African foreland
(Nile river deep sea fan). The reprocessing involved re-generation of stack sections
from the original tapes, migration and depth conversion. Pre-stack depth
migration was also performed on selected parts of the profiles with Geodepth ©
software. The migration velocity focusing analysis and grid tomography in
Geodepth © was also used to study the velocity distribution and define possible
facies changes in the salt sequence.
The development of the group’s capabilities in 3-D processing continued with the
MICA project. The aim of this project, funded by the ‘Fondo di Trieste’, was to
define the flow of underground water in the zone of the Carso. Two high resolution
land 3-D surveys were planned in the project; one was acquired in the early part of
the year, whilst the second towards the end of the year. The processing group was
involved both in the preparatory phase and in the processing of the recorded data.
Notwithstanding the problem of lack of high frequencies in data recorded on land,
the 3-D stack cube of the first survey produced good results in the area of interest
after the application of residual static correction routines.
The group has continued its collaboration with OCSA (Orellana Consultores S.A.
Madrid), processing a number of high resolution land lines to plan the best routing
for rail and road tunnels under mountainous regions. These data tend to be
inherently noisy and lacking in continuous reflections due to the deformed, often
metamorphic, areas in which they are recorded. Careful noise reduction and
continuity enhancement routines have been used in the final sections. Continued
close ties with other academic institutions produced a number of small processing
projects. Two 3-D surveys were processed with the University of Trieste (DINMA),
one line in the Acqua Profonda project for the local Friuli Venezia Giulia region
(also with DINMA), and a line acquired in Sardegna by the University of Cagliari.
The recovery and archiving of old multi-channel seismic data has continued to be
an important part of the group’s activities. All the Mediterranean data recorded by
OGS in the seventies, and about 70% of the data recorded by OGS in the Antarctic
in recent years, have been transcribed from their original field format to SEG-Y on
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