Imaging shallow gas migration pathways in a mud‐volcano province using an autonomous underwater vehicle (Malta Plateau, Mediterranean Sea)

Abstract

Data acquired by an autonomous underwater vehicle (AUV) towing a source (1600–3500 Hz) and a horizontal array of hydrophones have been analysed to image discrete, isolated or even a small cluster of scatterers within the sediment, to determine shallow migration paths of hydrocarbons in a mud volcano system of the Malta Plateau. An algorithm based on a semblance function was applied to the acoustic data to highlight scatterers rather than interface reflections. The resulting scatterer map, obtained along the AUV track, generated a pseudo‐three‐dimensional coverage of the study area, with a horizontal and vertical resolution of roughly 3–5 m and 5–10 m, respectively. This map was combined with high‐resolution bathymetric and backscattering seafloor maps obtained from previous explorations. This integrated dataset provides new evidence for the role of fault zones as a preferential path for gas/fluid migration and reveals the intermittent activity of seeping gas. The data show, in particular, that gas bubble slugs, i.e. discontinuous gas columns, rise through Plio‐Quaternary sediments along a complex system of conduits terminating at the surface into quiescent mud volcanoes. The gas flux is facilitated by the regional stress field that results in dilatant conditions on the mapped fault zones.

The image‐source method: a tool for geoacoustic inversion

“…; Savini et al . ). For this experiment the receiving array was 32 elements with a spacing of 21 cm, with the first element 33.5 m behind the source.…”

La Geologia Marina in Italia - Terzo Convegno dei geologi marini italiani

“…a case study from the Malta Plateau (Sicily Channel) The analysis of seismic data aimed at imaging discrete features, rather than the geometry of sedimentary layers (Pinson and Holland, 2016), is a more recent and less common technique, only recently adopted to investigate the sub-seafloor in a seep system (Savini et al, 2018). Discrete features can be defined as heterogeneities with aspect ratios in the neighbourhood of unity, instead of layers (i.e.…”

Characterizing Håkon Mosby Mud Volcano (Barents Sea) cold seep systems by combining ROV-based acoustic data and underwater photogrammetry

“…The MVs dome-shaped landforms can largely vary in diameter (up to a few kilometers) and heights (up to a few tens of meters above adjacent seafloor) (Mazzini and Etiope, 2017). Their discovery at the seafloor generally involves ship-based research surveys carried out using a combination of acoustic remote sensing techniques to collect high-resolution bathymetric measurements and seafloor backscattering data (Judd and Hovland 2007;Savini et al, 2018) using multibeam echosounders (MBES). However, as the water depth increases, the resolution of ship-based MBES surveys decreases (Mayer et al, 2018;Savini et al, 2021).…”