Hypothesis for a Migrating Conjugate Relay Zone in the Messina Strait, Southern Italy
(abstract submitted to the Tidalites Conference, early May, 2022: https://www.tidalites2022.it/)
1Dorsey, R.J.,2Longhitano, S.G., 3Chiarella, D.
(1) Department of Earth Sciences, University of Oregon, Eugene, OR (USA); (2) Department of Sciences, University of Basilicata, Potenza (Italy); (3) Department of Earth Sciences, Royal Holloway University of London (UK)
The Messina Strait (MS) is a modern, 3-km-wide tide-dominated passageway that separates the Italian peninsula from Sicily in the central Mediterranean Basin (Fig. 1A). The MS sits in a tectonically active region where seismogenic normal faults, sedimentary facies of Plio-Pleistocene deposits, and age of uplifted marine terraces provide a record of rapid extension and vertical crustal motions driven by southeastward rollback of the Calabrian subduction zone. Southern Calabria and northeast Sicily occupy a microplate bounded by active NW-striking strike-slip faults that mark the surface expression of growing tears in the subducting Ionian oceanic slab (Fig. 1A). Within this setting, large water masses of the Ionian and Tyrrhenian seas are compressed daily through the MS to produce horizontally-amplified tidal currents and a resulting wide range of erosional and depositional tidal processes (Longhitano, 2018). The bathymetric and geomorphic features of the MS are known to be tectonically controlled, yet their governing fault geometries and fault-kinematic processes remain poorly understood.
A review of published studies in southern Italy reveals a distinctive fault pattern that is best described as a conjugate relay zone (c.f. Childs et al., 2019), where displacement on opposed-dipping normal faults is transferred along-strike through a zone of overlapping extensional conjugate faults. The MS persists today within such a zone of overlap where strain is transferred from NW-dipping normal faults in southern Calabria to the SE-dipping Messina-Taormina normal fault offshore of northeast Sicily (Fig. 1B). The epicenter of the 1908 M 7.1 Messina earthquake is located roughly in the center of this relay zone. The narrow hook-shaped constriction at the northern exit of the MS is defined by pronounced plan-view curvature in facing conjugate normal faults that may reflect large strain gradients and local rotations near active fault tips in the locus of modern fault interactions, accommodated by slip on the offshore oblique-dextral Capo Peloro fault. Pleistocene marine terraces preserved at elevations up to 1.3 km asl in southern Calabria (Fig. 1B; Roda-Boluda and Whittaker, 2017; Antonioli et al., 2021, Meschis et al., 2022) record northwestward migration of normal faults in the past ~1 Myr. We speculate that a set of en-echelon normal faults at the eastern margin of the Messina Strait (west flank of Aspromonte Mts.) formed by northward migration of normal faults in response to NE-ward propagation of the Messina-Taormina fault (Fig. 1B). This hypothesis makes a number of testable predictions that could be evaluated in future work. For example, if fault interactions in the relay zone control preferential directions of incoming and outgoing tidal flows, they may thus influence the asymmetric partitioning of modern depositional environments and help to explain observed differences in sedimentary deposits north and south of the narrow MS exit.
