P-wave velocity modelling on the West Sardinia margin
|Author(s)||Afilhado Alexandra1, Moulin Maryline2, Aslanian Daniel2, Schnurle Philippe2, Klingelhoefer Frauke2, Nouze Herve2, Rabineau Marina3, Leroux Estelle3, Beslier Marie-Odile4|
|Affiliation(s)||1 : Instituto Dom Luiz, Portugal
2 : Ifremer, France
3 : CNRS, France
4 : Université Nice Sophia Antipolis, France
During the SARDINIA experiment, CHIRP profiles, bathymetry data, three coincident MCS reflection and wide-angle seismic profiles, and one single MCS reflection profile were collected on the West Sardinia margin. The MCS reflection data was acquired using a 4.5 km 360-trace digital streamer and a tuned airgun array of 8260 cubic inches, which was towed at a depth of 18-28 m. A total of 48 ocean bottom seismometers/hydrophones (OBS/OBH) from Ifremer, University of Brest, and Geomar Kiel were deployed on the West Sardinia margin, spaced every 7 nmi (~13 km). In five locations, three OBS were deployed at the same place to ensure the collection of data.
The airgun array consists of 16 airguns ranging from 100 cubic inch G-guns to 16 L Bolt airguns, with main frequencies centered around 10-15 Hz. The airguns were tuned to the first bubble, to enhance low frequencies and ensure deep penetration. The shot interval was 60 s at an average speed of 5 knots, which translates to a trace spacing of about 140-150 m. The sample rate was 8 ms for the micrOBS, 5 ms for the Geomar, and 4 ms for the OldOBS. A total of 3573 shots (profile GH: 1130, profile G2H2: 1214) were fired by the air gun array.
Profiles GH and G2H2, which are 160 and 200 km long transects, respectively cross the West Sardinia margin from the continental shelf to the “atypical” oceanic crust. Twenty-one ocean bottom seismometers (OBS) were deployed on the G2H2 profile, whereas sixteen were deployed on the GH profile. Additionally, the shots on this profile were recorded by eight land seismic stations (OSIRIS stations from the University of Brest and Geosciences Azur) that extended the marine profile ~150 km onshore.
For the two profiles only 33 instruments were used in the wide-angle modeling, since four instruments (OBSS06, 18a, 30a, and 30c) did not record properly.
We propose here the velocity models (v.in files) of the 2 main profiles located on the West sardinian margin, Profile K7L2, located on the shelf and parallel to the margin, is not presented since most of the deep arrivals are masked by the presence of sea-bottom multiples, preventing an accurate wide-angle model.