Numerical modeling of tidal notch sequences on rocky coasts of the Mediterranean Basin

Tidal notches have had the potential to form at sea level from similar to 6.5kyr B.P. in the Mediterranean Basin and preserve a symmetrical shape comparable to a quadric polynomial. Continuous erosion, predominantly by biological agents, affects a limestone cliff face from low- to high-tide level at <1mm/yr. Statically determined, the roots of a quadric polynomial are defined by the tidal range representing the limits of effective erosion. However, gradual variations of eustatic sea level rise (slow) and coseismic uplift/subsidence (fast) in tectonically active regions contribute to vertical shifts in the erosional base at coastlines. As a consequence, the cliff morphology gets modified through time resulting in widening, deepening, and separation of notches and possible overprinting of older features. In order to investigate successive modifications of coastal cliff morphology, we developed a numerical model that considers the erosion rate, the erosion zone relative to sea level, the regional sea level curve, and tectonic motion. The results show how slow and rapid sea level changes bias the modern cliff face and highlight that the present-day notch sequence from top descending to sea level is not inevitably of decreasing age. Furthermore, the initiation of notch formation is not necessarily linked to the date of a certain seismic event. Especially in extensional tectonic settings where coseismic uplift is low and coastal morphological marks are not as distinct, knowledge about coastal evolution is beneficial for paleoseismological research.