Active degassing across the Maltese Islands (Mediterranean Sea) and implications for its neotectonics

The Maltese Islands, located in the central Mediterranean Sea, are intersected by two normal fault systems
associated with continental rifting to the south. Due to a lack of evidence for offshore displacement and insignificant
historical seismicity, the systems are thought to be inactive and the rift-related deformation is believed
to have ceased. In this study we integrate aerial, marine and onshore geological, geophysical and geochemical
data from the Maltese Islands to demonstrate that the majority of faults offshore the archipelago underwent
extensional to transtensional deformation during the last 20 ka. We also document an active fluid flow system
responsible for degassing of CH4 and CO2. The gases migrate through carbonate bedrock and overlying sedimentary
layers via focused pathways, such as faults and pipe structures, and possibly via diffuse pathways, such
as fractures. Where the gases seep offshore, they form pockmarks and rise through the water column into the
atmosphere. Gas migration and seepage implies that the onshore and offshore faults systems are permeable and
that they were active recently and simultaneously. The latter can be explained by a transtensional system involving
two right-stepping, right-lateral NW-SE trending faults, either binding a pull-apart basin between the
islands of Malta and Gozo or associated with minor connecting antitethic structures. Such a configuration may be
responsible for the generation or reactivation of faults onshore and offshore the Maltese Islands, and fits into the
modern divergent strain-stress regime inferred from geodetic data.