Unraveling the Adriatic Plate Configuration beneath Albania with Teleseismic Full Waveform Inversion

The eastern margin of the Adriatic plate stands out for its tectonic complexity and geohazard potential in Europe, which are dominated by the northeast-directed subduction and collision of the Adriatic plate with the Eurasian plate beneath the Balkan. Beneath the southern Dinarides (northern Albania), the Adriatic plate is believed to be shallower than 150 km whereas the plate penetrates down to 200 km depth beneath the northern Hellenides (central and southern Albania). Further south, the Kefalonia transform fault system (KTFS, northwestern Greece) is believed to represent the transition from continental subduction of Adriatic plate to the oceanic subduction of the Ionian plate. Recent studies proposed different conception models including horizontal and vertical slab tearing beneath these transitions. Despite the importance of this region, seismic imaging is still insufficient to resolve these fundamental geodynamic processes.

To answer these important geodynamic questions, we employ the advanced wavefield-injection teleseismic full waveform inversion (TELEFWI) to image the seismic velocity structure beneath Albania. The TELEFWI explores waveform recordings from 9 high-quality teleseismic earthquakes recorded by 50 broadband stations from the ANTICS array (Albanian Tectonics of Continental Subduction, FDSN code X3, 2022-2024). TELEFWI reveals detailed structures from the crust down to 220 km in depth, with spatial resolution of 20 km for the P wave velocity from crust down to the upper mantle and 15 km for the S wave in the crust and uppermost mantle.

The new velocity model displays a strong eastward-dipping high-velocity anomaly in the upper mantle down to at least 150 km for the whole study domain, which we suggest to be the expression of the subducting Adriatic plate. The Adriatic plate displays westward-retreating pattern in the upper mantle to the coast beneath southern Albania. Meanwhile, multiple high velocity anomalies in depth probably indicates multi-phase slab break-off events at depths of 100 to 150 km beneath southern Albania. In contrast, the Adriatic plate remains relatively flat for over 100 km from the coast to the inland and then dips into the upper mantle beneath northern Albania, but the anomaly is relatively weaker compared to the south. Strong low-velocity anomalies in the upper crust are observed beneath the basins, probably representing the thick sediment layer.

In summary, this study provides a high-resolution velocity model for the first time based on teleseismic full waveform inversion and sheds light on the Adriatic plate configuration beneath its eastern margin.