MOIST Acquisition The first profile to be acquired was the Moine and Outer Isle Seismic Traverse (MOIST). This roughly 185 km long line ran west–east, north of the Scottish mainland, intending to image the main Caledonian structures known onshore, such as the
Outer Isles Fault Zone and the
Moine Thrust Belt. The line was acquired in March 1981 by
Western Geophysical and processing was complete by October of that year. It used a 3,000 m
hydrophone streamer, with a airgun array as its source. The record length was 15 seconds two-way travel time (TWTT).
Interpretation The MOIST profile shows a series of deep
half-graben basins, bounded to the west by easterly dipping
extensional faults, part of the
West Orkney Basin. The faults coincide with major east-dipping zones of reflectivity extending down to the lower crust. These have been interpreted to be Caledonian thrust structures, with the Outer Isles Fault clearly imaged. No direct correlation was possible between the Moine Thrust Belt onshore and the offshore structure. The MOIST line was also interpreted to show whole
lithosphere extensional faulting, although later interpretation suggested that the major normal faults did not pass through the
Moho.
Interpretation SWAT Acquisition The South West Approaches Traverse (SWAT) consisted of a series of eleven profiles acquired between September and November 1983 by Seismic Profilers Ltd, with a total length of 1600 km. The profiles were shot across the North and South Celtic Sea Basins, the Western Approaches Basin and the Western and Eastern Channel Basins. Processing was carried out by Seismograph Services Ltd. (SSL).
Interpretation SALT Two short profiles, named for the
Zechstein salt layer found over large parts of the North Sea that had caused problems with deep seismic penetration, were acquired to test the feasibility of deep profiling over the area in preparation for the much larger NSDP survey.
Acquisition The two profiles, SALT 1 and SALT 2 were shot in 1983 along parts of a previously acquired seismic refraction profile.
Interpretation When this survey was shot, sufficient deep reflection data had been acquired to establish a pattern of reflectivity for the crust of the North Sea, with the Moho interpreted at the base of a band of reflections. The SALT survey showed that this was consistent with the Moho interpreted from earlier seismic refraction data.
DRUM Acquisition The DRUM profile was named as an acronym for Deep Reflections in the Upper Mantle and for
Drummond (Drum) Matthews the BIRPS scientific director. It was acquired and processed in 1984 by GECO, with an unprecedented record length of 30 seconds TWTT.
GRID and SLAVE Acquisition The GRID profiles were acquired to provide a better coverage of structures already identified off the north coast of Scotland by MOIST, WINCH and DRUM. The SLAVE (Synthetic Large Aperture Velocity Experiment) profile was a two-ship wide-aperture experiment that formed part of the overall grid of lines. The data was recorded to record lengths of between 15 and 60 seconds of two-way travel time (TWTT).
Interpretation This set of profiles followed up on the MOIST, DRUM and WINCH1 and WINCH2 profiles, forming an overall grid pattern, allowing the extent and orientation of the deeper reflections previously imaged to be investigated. The Flannan Thrust was shown to be continuous over almost the whole dataset. Its orientation matches that of known Caledonian structures, such as the Outer Isles Fault and Moine Thrust Zone, although this trend is also similar to structures of both
Proterozoic and post-Caledonian age. The W-reflector was confirmed to be sub-horizontal in orientation, but of limited lateral extent.
Interpretation The most important observation from the SHET survey was that the Moho was apparently offset by the
Walls Boundary Fault, a major
strike-slip fault formed during the later part of the Caledonian Orogeny, thought to be part of the
Great Glen Fault system.
NEC Acquisition The 237 km long North East Coast (NEC) profile was shot in October 1985 by Geco, with processing carried out by SSL. It ran from near
Montrose in Scotland to near
Hartlepool in England. The record length varied between 15 and 16 seconds TWTT, imaging down to an estimated 50 km. It was designed to provide information on the
collision zone between the
microcontinent of
Avalonia and
Laurentia, particularly the location and geometry of the
Iapetus Suture.
Interpretation WAM The WAM (Western Approaches Margin) profile was shot in 1985 to investigate the structure of part of the UK continental margin.
WIRE The WIRE (West of IREland) profiles were shot in 1987.
MOBIL The MOBIL (Measurements Over Basins Imaging the Lithosphere) dataset was acquired after a gift of shiptime on the
Mobil Search seismic vessel in 1987.
WISPA The WISPA (Wearside Integrated S-wave and P-wave Analysis) experiment was acquired in 1988. This was the only entirely onshore seismic experiment carried out by the BIRPS group.
BABEL The BABEL (Baltic and Bothnian Echoes from the Lithosphere) profiles were acquired in 1989 by a consortium of scientific institutions from Sweden, Denmark, Finland, Germany and the United Kingdom (the BIRPS group).
SWABS The SWABS (Seismic Wide-Angle and Broadband Survey) was a two-ship seismic experiment shot in 1992 in the North Sea.
TIMOR & DAMAR The TIMOR and DAMAR surveys were shot in 1992 across the
Banda Arc.
Acquisition These lines were shot by Geco using the
M/V GECO-Kappa with a 4.6 km long hydrophone streamer and a 120-litre airgun array as its source. The shot intervals varied between the surveys with both 50 m and 100 m being used. The TIMOR profile was recorded to 23 seconds TWTT, while the DAMAR profile, which had a deeper target, was recorded to 35 seconds TWTT.
CHIX The CHIX survey was a set of three profiles shot in 1996 across the
Chicxulub crater.
Acquisition The profiles were shot using the
Geco Sigma vessel to a record length of 18 seconds two-way time with a total length of nearly 650 km. Chix-A was shot parallel to the coast about 20 km offshore, while Chix-B and Chix-C were shot in a NW–SE and NNE–SSW direction respectively. In addition to the conventional seismic reflection recording, ocean bottom seismometers (OBS) were deployed offshore and conventional seismometers were located on the onshore extension of Chix-B and C and along the coast. These extra seismometers were used to obtain information about the velocity structure. Offshore recording used a dual configuration streamer, set up to provide higher resolution in the upper crust and lower resolution of the whole crust. These two data types were processed using different approaches. == References ==