Analysis of the 2019 M w 6.4 Durrës, Albania, aftershock sequence: basement involved thrusting at the eastern Adriatic plate margin

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SUMMARY The 2019 M 6.4 Durrës earthquake in Albania caused severe loss of life and economic damage, highlighting the seismic hazard along the Adriatic–European plate boundary. This study provides the first high-resolution analysis of the aftershock sequence based on data from a dense local seismic network deployed three weeks after the mainshock. Using machine-learning detection and phase-picking tools, we identified 19 152 aftershocks (Ml − 1.8 to 4.6; Mc ≈ 1) over a nine-month period. Based on a newly derived 1-D velocity model with station corrections, accounting for large vertical and lateral velocity variations, we relocated the events applying cross-correlation based differential traveltimes and the double-difference algorithm. The refined seismicity images clearly reveal several subparallel ∼30° NE-dipping blind fault structures; the most prominent one, between 12 and 18 km depth, probably hosted the Durrës mainshock. The blind thrust faults lie beneath thick sediments and cut through a carbonate platform and into the Adriatic basement, indicating thick-skinned deformation. Our observations may be interpreted as incipient large-scale slicing and underplating of subducted Adriatic crust. Additional shallow seismicity within a duplex structure in the hanging wall points is relevant for seismic hazard, as even a relatively moderate earthquake occurring close to the surface could cause significant damage.

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