Preprints
https://doi.org/10.5194/essd-2022-258
https://doi.org/10.5194/essd-2022-258
 
11 Aug 2022
11 Aug 2022
Status: this preprint is currently under review for the journal ESSD.

Reprocessed 2-D airgun seismic reflection data SALTFLU (salt deformation and sub-salt fluid circulation in the Algero-Balearic abyssal plain) in the Balearic promontory and the Algerian basin

Simon Blondel1,2, Jonathan Ford1, Aaron Lockwood3, Anna Del Ben2, and Angelo Camerlenghi1 Simon Blondel et al.
  • 1National Institute of Oceanography and Applied Geophysics – OGS, Trieste, Italy
  • 2Department of Mathematics and Geosciences, University of Trieste, Trieste, Italy
  • 3Shearwater GeoServices Inc, Gatwick, United Kingdom

Abstract. In an ever more challenging context for the acquisition of seismic data in the Mediterranean Sea, reprocessing to improve the quality of legacy data has become increasingly important. This work presents the newly reprocessed, open access dataset SALTFLU acquired in the Algerian basin by the National Institute of Oceanography and Applied Geophysics (OGS) in 2012. We apply a ‘broadband’ reprocessing strategy adapted for short-offset, deep water airgun reflection seismic data and assess if the reprocessed images provide new geological insights on the Mediterranean sub-surface. The workflow relies on an integrated approach combining geophysics and geological interpretation to iteratively build the velocity model. In this way we aim to tackle some of the challenges linked to imaging complex geological structures containing high velocity contrasts with 2-D, short-offset seismic data. We first broaden the bandwidth of the data through multi-domain de-noising, deghosting and a source designature using an operator derived from the seabed reflection. We then perform iterative migration velocity analysis, pre-stack time migration and multiple attenuation in the Radon domain to obtain time-migrated images. The initial velocity model is derived from the resulting time migration velocities, and geologically driven model updates are generated using a combination of travel-time tomography, seismic interpretation of the major salt horizons and velocity gradient flooding. The gradient flooding aims to reproduce the large scale first-order velocity variations, while the travel-time tomography aims to resolve the smaller second-order velocity variations. The results improve our deep geological knowledge of the under-explored Algerian basin down to the base salt and the pre-salt. Fluid indicators are imaged within the Plio-Quaternary of the Algerian basin, which we interpret as thermogenic or biogenic gas sourced from either the Messinian Upper Unit or from the pre-salt, migrating through a hydro-fractured salt. The reprocessed data image lateral and vertical seismic facies variation within the Messinian units that could shed new light on the tectono-stratigraphic processes acting during the Messinian Salinity Crisis. It also reveals numerous previously unresolved volcanic structures within the Formentera basin.

Simon Blondel et al.

Status: open (until 27 Oct 2022)

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Simon Blondel et al.

Data sets

Multi-channel seismic reflection profiles SALTFLU (Salt deformation and sub-salt fluid circulation in the Algero-Balearic abyssal plain) - Pre-Stack Kirchhoff Time & Depth Migration 2022 Simon Blondel, Jonathan Ford https://doi.org/10.5281/zenodo.6912214

Simon Blondel et al.

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Short summary
This manuscript describes the re-processing flow applied to legacy multichannel seismic data in the deepwater Algerian basin, now open-access. The processing flow was designed based on the most robust and modern methods used in the industry and can be taken as example for other marine multi-channel datasets. Many new geological features are succinctly described, and are yet to be understood.