The progressive southeastward advance of the Calabria-Apulia collision recorded by uplifted Ionian marine terraces

The Calabrian forearc separated from Sardinia ~10 Ma and migrated to the ESE, creating an oceanic basin (the Tyrrhenian Sea) in its wake and colliding obliquely with Apulia to build the southern Apennines. The time transgressive, spatially asymmetric nature of oblique collisions leads to along-strike migration of active geologic processes. Lack of evidence for large thrust earthquakes and conflicting geodetic evidence of Calabria-Apulia convergence contribute to the predominant belief that this process has completely ceased. Indicators of thrusting and steady state uplift from the Pleistocene into the Holocene are evident from field observations in the southernmost internal Apennines (Pollino Massif) and marine terrace ages on the external Apennines along the Gulf of Taranto (Metaponto). Terrace uplift rates increase dramatically southward, reaching a maximum of 1 mm/yr at the boundary between Pollino and Metaponto. Uplift rates may continue to increase southward in tandem with the structural and topographic relief across the Apenninic core, but correlation of marine terraces southward to the Sibari Plain becomes problematic because of steep slopes, erosion, and mass wasting. Any chronology of marine terrace ages used for determination of uplift rates and variability will need confirmation by abundant independent age constraints. Constraining uplift rates may be further complicated by a “corrugated detachment” (CD), a regionally exposed kinematic contact along the topographic axis of the southern Apennines between underlying carbonate and overlying flysch. This surface is believed to represent an active gravity-driven detachment with ESE tectonic transport down–slope of the collision wedge. Ductile deformation features within the exposed carbonate suggest burial depths of 1-2 km, and thus a currently active CD might be buried beneath the marine terraces ESE of the Pollino Massif. An active detachment above a rising footwall could lead to underestimates of tectonic uplift rates, and consequently misinterpretations of seismic risk. Recent advances in InSAR technology can resolve elastic deformation preceding seismogenic fault ruptures, as well as aseismic motion on faults, folds, and slumps through high-resolution velocity fields derived from accumulated datasets over the past decade. A coordinated effort coupling field-based observation, a detailed geochronology of marine and fluvial deposition, and high resolution InSAR analyses is needed to determine whether the current deformation is consistent with a continued Calabria-Apulia collision and to better constrain the seismic hazard in south Italy.