Clusters of megaearthquakes on upper plate faults control the Eastern Mediterranean hazard

Abstract

The Hellenic subduction margin in the Eastern Mediterranean has generated devastating historical earthquakes and tsunamis with poorly known recurrence intervals. Here stranded paleoshorelines indicate strong uplift transients (0–7 mm/yr) along the island of Crete during the last ~50 kyr due to earthquake clustering. We identify the highest uplift rates in western Crete since the demise of the Minoan civilization and along the entire island between ~10 and 20 kyr B.P., with the absence of uplifted Late Holocene paleoshorelines in the east being due to seismic quiescence. Numerical models show that uplift along the Hellenic margin is primarily achieved by great earthquakes on major reverse faults in the upper plate with little contribution from plate‐interface slip. These earthquakes were strongly clustered with recurrence intervals ranging from hundreds to thousands of years and primarily being achieved by fault interactions. Future great earthquakes will rupture seismically quiet areas in eastern Crete, elevating both seismic and tsunami hazards.

Present‐day crustal stress field in Greece inferred from regional‐scale damped inversion of earthquake focal mechanisms

“…The second group occurs at shallower depths (<20 km); it exhibits fault plane dips of 30° or more and is probably the manifestation of a fault splaying from the plate interface in the upper plate. This splay fault is partly responsible for the uplift of the western Crete shoreline and is thought to be the source of the megathrust earthquake and tsunami in 365 A.D. and other similar earthquakes during the last 50 kyr [ Shaw et al ., ; Stiros , ; Mouslopoulou et al ., ]. In this framework, the horizontal σ 1 axes offshore SW Peloponnese with NNE to NE‐SW directions indicate the compression of the upper plate owing to the northward subduction of the African lithosphere.…”

Temporally Constant Quaternary Uplift Rates and Their Relationship With Extensional Upper‐Plate Faults in South Crete (Greece), Constrained With 36Cl Cosmogenic Exposure Dating

“…Crete is situated above the Hellenic subduction zone (HSZ) and has been used to study the relationship between uplift and slip associated with the HSZ (Gallen et al, ; Papadimitriou & Karakostas, ; Shaw et al, ; Shaw & Jackson, ; Strobl et al, ). Observations from uplifted palaeoshorelines (e.g., Gallen et al, ; Mouslopoulou, Begg, et al, ; Mouslopoulou, Nicol, et al, ; Pirazzoli et al, ; Shaw et al, ; Tsimi et al, ), Paleolithic sites (Strasser et al, ), alluvial fans (Mouslopoulou et al, ; Pope et al, ), and other geomorphological and biological features (Kelletat, ; Shaw et al, ) along its south and west coasts have been used to discuss the relationships between slip on the subduction interface, thrust faults in the overlying wedge, and historic tsunamigenic earthquakes (Ganas & Parsons, ; Shaw et al, ; Shaw & Jackson, ; Stiros, ). However, less attention has been given to the role of active normal faulting in influencing uplift, a phenomenon that is widespread on Crete (Angelier, ; Armijo et al, ; Caputo et al, ; Gallen et al, ; Ganas 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, ; Caputo et al, ; Gallen et al, ; Ganas & Parsons, ; Meier et al, ; Mouslopoulou, Nicol, et al, ; Shaw et al, ; Strobl et al, ; Taymaz et al, ; Tiberti et al, ). 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 (Becker et al, ; Bohnhoff et al, ; Caputo et al, ; Doutsos & Kokkalas, ; Howell et al, ; Kokinou et al, ; Meier et al, ; Papazachos, ; Shaw & Jackson, ; Taymaz et al, ).…”

“…Investigations using uplifted hangingwall and footwall marine terraces, 2‐D viscoelastic modeling, and sedimentary correlations have led to a large variety of uplift estimates along the south coast of Crete from 0.2 to 7.7 mm/year over timescales since the late Quaternary (~600 ka) to the present day (Gaki‐Papanastassiou et al, ; Gallen et al, ; Gallen & Wegmann, ; Meulenkamp et al, ; Mouslopoulou et al, ; Mouslopoulou, Begg, et al, ; Mouslopoulou, Nicol, et al, ; Shaw et al, ; Skourtsos et al, ; Strasser et al, ; Strobl et al, ; Tiberti et al, ). Additionally, some authors propose that uplift rates have significantly varied over time (Gallen et al, ; Mouslopoulou, Nicol, et al, ; Tiberti et al, ).…”

“…Investigations using uplifted hangingwall and footwall marine terraces, 2‐D viscoelastic modeling, and sedimentary correlations have led to a large variety of uplift estimates along the south coast of Crete from 0.2 to 7.7 mm/year over timescales since the late Quaternary (~600 ka) to the present day (Gaki‐Papanastassiou et al, ; Gallen et al, ; Gallen & Wegmann, ; Meulenkamp et al, ; Mouslopoulou et al, ; Mouslopoulou, Begg, et al, ; Mouslopoulou, Nicol, et al, ; Shaw et al, ; Skourtsos et al, ; Strasser et al, ; Strobl et al, ; Tiberti et al, ). Additionally, some authors propose that uplift rates have significantly varied over time (Gallen et al, ; Mouslopoulou, Nicol, et al, ; Tiberti et al, ). Studies to determine uplift rates have employed a mixture of dating techniques with many attempting to explore long‐term uplift using accelerator mass spectrometry 14 C radiocarbon dating on marine shells (Mouslopoulou, Begg, et al, ; Mouslopoulou, Nicol, et al, ; Shaw et al, , ; Shaw, ; Strasser et al, ; Tiberti et al, ), which has a maximum dating span of around ~50 ka (Reimer et al, ); other methods include 10 Be exposure dating (Strobl et al, ), OSL geochronology (Gallen et al, ), and U‐Series measurements (Angelier ; Gaki‐Papanastassiou et al, ).…”