Subduction and vertical coastal motions in the eastern Mediterranean

Abstract

S U M M A R YConvergence in the eastern Mediterranean of oceanic Nubia with Anatolia and the Aegean is complex and poorly understood. Large volumes of sediment obscure the shallow structure of the subduction zone, and since much of the convergence is accommodated aseismically, there are limited earthquake data to constrain its kinematics. We present new source models for recent earthquakes, combining these with field observations, published GPS velocities and reflection-seismic data to investigate faulting in three areas: the Florence Rise, SW Turkey and the Pliny and Strabo Trenches. The depths and locations of earthquakes reveal the geometry of the subducting Nubian plate NE of the Florence Rise, a bathymetric high that is probably formed by deformation of sediment at the surface projection of the Anatolia-Nubia subduction interface. In SW Turkey, the presence of a strike-slip shear zone has often been inferred despite an absence of strike-slip earthquakes. We show that the GPS-derived strain-rate field is consistent with extension on the orthogonal systems of normal faults observed in the region and that strike-slip faulting is not required to explain observed GPS velocities. Further SW, the Pliny and Strabo Trenches are also often interpreted as strike-slip shear zones, but almost all nearby earthquakes have either reverse-faulting or normal-faulting focal mechanisms. Oblique convergence across the trenches may be accommodated either by a partitioned system of strike-slip and reverse faults or by oblique slip on the Aegean-Nubia subduction interface. The observed late-Quaternary vertical motions of coastlines close to the subduction zone are influenced by the interplay between: (1) thickening of the material overriding the subduction interface associated with convergence, which promotes coastal uplift; and (2) subsidence due to extension and associated crustal thinning. Long-wavelength gravity data suggest that some of the observed topographic contrasts in the eastern Mediterranean are supported by mantle convection. However, whether the convection is time dependent and whether its pattern moves relative to Nubia are uncertain, and its contribution to present-day rates of vertical coastal motions is therefore hard to constrain. The observed extension of the overriding material in the subduction system is probably partly related to buoyancy forces arising from topographic contrasts between the Aegean, Anatolia and the Mediterranean seafloor, but the reasons for regional variations are less clear.

Temporally Constant Quaternary Uplift Rates and Their Relationship With Extensional Upper‐Plate Faults in South Crete (Greece), Constrained With36Cl Cosmogenic Exposure Dating

“…Extensional faults that trend parallel to the Hellenic arc, such as those discussed in this study, exist offshore and onshore southern Crete (e.g., Sfakia fault and Selia/Assomatos faults, Figure a), Kythira, the Mani Peninsula (Peloponnese), and western Peloponnese (Armijo et al, ; Gaki‐Papanastassiou et al, ; Kassaras et al, ; Kokinou & Kamberis, ; Mascle et al, ; Papanikolaou et al, ; Papoulia et al, ; Papoulia & Makris, ; Tsimi et al, ; Wardell et al, ) and are in many places associated with uplifted marine terraces (e.g., Angelier, ; Athanassas & Fountoulis, ; Gaki‐Papanastassiou et al, ; Kelletat et al, ). The presence of terraces and onshore/offshore extensional faults throughout the rest of the Hellenic Arc leads us to suggest the observed uplift along these coastlines could, in part, also be controlled by upper‐plate faults; there is evidence that terraces along the western Peloponnese are on a length scale associated with upper‐plate extensional faults (Howell et al, ).…”

“…The cause of uplift on Crete is debated and suggested to result from underplating on the subduction interface, reverse motion on the megathrust, thrusting and oblique slip faulting in the forearc, and active normal faulting (Angelier et al, 1982;Caputo et al, 2010;Gallen et al, 2014;Ganas & Parsons, 2009;Meier et al, 2007;Shaw et al, 2008;Strobl et al, 2014;Taymaz et al, 1990;Tiberti et al, 2014). Geodetic, seismological, and geological evidence suggests compressional, extensional, and strike-slip tectonics onshore and offshore southern Crete as seen by the analysis of fault plane solutions and microseismicity studies Bohnhoff et al, 2005;Caputo et al, 2010;Doutsos & Kokkalas, 2001;Howell et al, 2017;Kokinou et al, 2012;Meier et al, 2007;Papazachos, 1990;Taymaz et al, 1990). These studies show that thrust faulting occurs as a result of forearcnormal compression at depths linked to subduction to the south of Crete; additionally, Shaw et al (2008) suggested that reverse (high-angle) splay faults may cut the upper crust in western Crete; however, their existence was debated by Ganas and Parsons (2009) on the basis of a lack of compatible seismological data.…”

“…These studies show that thrust faulting occurs as a result of forearcnormal compression at depths linked to subduction to the south of Crete; additionally, Shaw et al (2008) suggested that reverse (high-angle) splay faults may cut the upper crust in western Crete; however, their existence was debated by Ganas and Parsons (2009) on the basis of a lack of compatible seismological data. The E-W and N-S trending normal faults accommodate arc-normal and arc-parallel extension (Angelier, 1979a;Armijo et al, 1992;Caputo et al, 2006;Caputo et al, 2010;Fassoulas, 2000;Floyd et al, 2010;Gallen et al, 2014;Gallen & Wegmann, 2016;Ganas et al, 2017;Howell et al, 2017;Kokinou et al, 2012;Peterek & Schwarze, 2004;Snopek et al, 2007), which is also reflected in Eurasian (upper) plate GPS motions that increase toward the southern edge of the plate in the location of Crete (Floyd et al, 2010;McClusky et al, 2000) and are quantified by Nocquet (2012) as~10 mm/year. Pleistocene uplift is visible in sequences of preserved marine terraces seen throughout the eastern and southern coasts of Crete (Angelier, 1979b;Gaki-Papanastassiou et al, 2009;Gallen et al, 2014;Peterek & Schwarze, 2004;Pirazzoli et al, 1982;Strobl et al, 2014).…”

Thermal history of the western Central Taurides fold-thrust belt: Implications for Cenozoic vertical motions of southern Central Anatolia

“…Seismicity (Kalyoncuoğlu et al, 2011;Howell et al, 2017) and seismic tomography (Biryol et al, 2011;van der Meer et al, 2018) show that the top of the Antalya slab is currently located below the Gulf of Antalya, more than 150 km southwest of Tauride thrusts that mark the Eocene plate boundary. This slab must contain the mantle underpinnings of Taurides, which have now sunk into the mantle.…”

Continental collisions and the origin of subcrustal continental earthquakes

“…The Florence Rise (Fig. 9, from Howell et al 2017) and Apscheron Sill across the middle of the Caspian Sea (Fig. 10) are two relatively small structures that have subducted oceanic lithosphere in the Alpine-Himalayan collision zone.…”