The Bortoluzzi Mud Volcano (Ionian Sea, Italy) and its potential for tracking the seismic cycle of active faults

Abstract

Abstract. The Ionian Sea in southern Italy is at the center of active interaction and convergence between the Eurasian and African–Adriatic plates in the Mediterranean. This area is seismically active with instrumentally and/or historically recorded Mw>7.0 earthquakes, and it is affected by recently discovered long strike-slip faults across the active Calabrian accretionary wedge. Many mud volcanoes occur on top of the wedge. A recently discovered one (called the Bortoluzzi Mud Volcano or BMV) was surveyed during the Seismofaults 2017 cruise (May 2017). High-resolution bathymetric backscatter surveys, seismic reflection profiles, geochemical and earthquake data, and a gravity core are used here to geologically, geochemically, and geophysically characterize this structure. The BMV is a circular feature ≃22 m high and ≃1100 m in diameter with steep slopes (up to a dip of 22∘). It sits atop the Calabrian accretionary wedge and a system of flower-like oblique-slip faults that are probably seismically active as demonstrated by earthquake hypocentral and focal data. Geochemistry of water samples from the seawater column on top of the BMV shows a significant contamination of the bottom waters from saline (evaporite-type) CH4-dominated crustal-derived fluids similar to the fluids collected from a mud volcano located on the Calabria mainland over the same accretionary wedge. These results attest to the occurrence of open crustal pathways for fluids through the BMV down to at least the Messinian evaporites at about −3000 m. This evidence is also substantiated by helium isotope ratios and by comparison and contrast with different geochemical data from three seawater columns located over other active faults in the Ionian Sea area. One conclusion is that the BMV may be useful for tracking the seismic cycle of active faults through geochemical monitoring. Due to the widespread diffusion of mud volcanoes in seismically active settings, this study contributes to indicating a future path for the use of mud volcanoes in the monitoring and mitigation of natural hazards.

One Year of Seismicity Recorded Through Ocean Bottom Seismometers Illuminates Active Tectonic Structures in the Ionian Sea (Central Mediterranean)

“…The occurrence of SDE events and their close correlation with the occurrence of microseismicity could indicate significant contamination of the bottom waters from saline (evaporate-type) CH4-dominated crustal-derived fluids. These were observed in the Ionian Sea, in correspondence of a mud volcano (the Bortoluzzi Mud Volcano; BMV) discovered during the SEISMOFAULTS cruise in May 2017 (Cuffaro et al, 2019). The BMV is one of many mud volcanoes offshore Calabria.…”

“…About 2,400 events were located by INGV seismological network. Bathymetric data were obtained from high resolution multibeam soundings during the SEISMOFAULTS first cruise (Cuffaro et al, 2019;Billi et al, 2020) and merged with DEMs from https://portal.emodnet-bathymetry.eu/.…”

“…1,2,3). Bathymetric map was obtained from high resolution multibeam collected during the oceanographic cruise of SEISMOFAULTS project (Cuffaro et al, 2019;Billi et al, 2020) and merged with DEMs from https://portal.emodnet-bathymetry.eu/. We now consider the detection capability of the OBS network.…”

“…The main tectonic structures including the Alfeo-Etna Fault and Ionian Fault (Polonia et al, 2016) are sketched in red. Bathymetric map was obtained from high resolution multibeam collected during the oceanographic cruise of SEISMOFAULTS project (Cuffaro et al, 2019;Billi et al, 2020) and merged with DEMs from https://portal.emodnet-bathymetry.eu/.…”

Nature and significance of rift-related, near-surface fissure-fill networks in fractured carbonates below regional unconformities

“…Given the evidence for fluid flux through the sediment-filled fractures, it seems likely that some sediment was ejected from the fracture system and effused at the surface; but marine mud volcanoes such as the Bortoluzzi volcano, offshore Calabria, frequently sit above major active fault zones and are formed through very similar processes (Cuffaro et al 2019).…”