Submerged notches, coastal changes and tectonics in the Rijeka area, NW Croatia

Submerged coastal notches characterize the coast of the wider Rijeka area, NW Croatian coast, Adriatic Sea. These notches originate from a notch formed approximately 2,000 years ago, their depth ranges between 0.50 and 1.15 m and their subsidence history is a matter of debate. A detailed study of all the available data in relation to the tectonics of the area was made using signal analysis techniques. Our analysis revealed that the notch depth reflects the superimposition of two different effects, a quasi-regional relative sea-level rise of about 55 cm, and of a subsequent, local, tectonic subsidence with amplitude gradually increasing to 60 cm in the vicinity of the major thrust in the Bakar Bakar–Vinodol area. Elastic dislocation modeling permitted to explain this last local subsidence in terms of loading of the footwall of this thrust and provide evidence for an unrecorded earthquake of minimum magnitude Mw 6.8, which occurred most probably in the last few centuries. This result indicates that the convergence between the Southern Alps and the Adria is at least partly accommodated by earthquakes, and puts some constraints in the estimations of the seismic risk in the wider region.