Water transport in the Earth's mantle: first evidence from seismograms of southern Tyrrhenian earthquakes

An unknown later seismic phase has been found on waveforms of intermediate-depth and deep earthquakes of the southern Tyrrhenian subduction system. The later phase, called the x-phase, is a compressional wave, which leaves the source travelling downwards and propagating in the deepest edge of the Ionian lithosphere. It is, then, transmitted to the surface and observed at stations towards north, hundreds of kilometres away, appearing few seconds after the direct P wave. The observation of the x-phase and its peculiar seismological features have implications on the petrology of the Ionian slab and on water transport in the upper mantle. An additional aspect, to be further explored, is the possible presence of a similar later arrival after the S waves, which may add more information about the origin of the waves. This paper introduces previous findings and presents new analyses on S waves, completing earlier results and interpretations.