CHRONOSTRATRIGRAPHY OF LATE QUANTERNARY MARINE TERRACES OF CRETE, GREECE: VERTICAL TECTONICS AND IMPLICATIONS FOR SEISMIC SLIP ON THE HELLENIC SUBDUCTION ZONE

Seismic coupling between the subducting slab and upper plate in subduction zones has emerged as a key consideration in understanding the genesis of great earthquakes, tsunamis, and the building of forearc topography. Despite ongoing convergence at the Hellenic subduction zone (HSZ) of ~40 mm/yr, there exists a paucity of well-documented great subduction thrust earthquakes. Comparison of vertical uplift signals between long-term (marine terraces) and short-term (GPS or InSAR) sources may provide insights into the seismic potential of the HSZ.

We've developed a regional marine terrace chronostratigraphy for the west and south coasts of Crete, Greece extending back to ~125 ka. A facies model incorporating erosional and depositional marine and near-marine terrestrial landforms was developed and includes deposits from offshore, nearshore, shoreface, backbeach, and alluvial fan environments. Flights of up to 6 discernable terrace levels exist and individual terrace elevations were determined via differential GPS. The chronostratigraphy is anchored by well-preserved and dated terrace flights at Phalasarna, Moni Chrysoskalitissas–Paleochora, Plakias–Damnoni, and Cape Trekalo.

The first ¹⁴C ages of Pleistocene terraces from Crete along with correlation to the eustatic sea level curve suggest long-term uplift rates of 1.5±0.5 mm/yr along the southwest and western coast. A prominent terrace assigned to the OIS 5a highstand decreases in elevation from 53 m at Paleochora to 27 m at Agh. Marina, a distance of 55 km. The prominent Holocene erosional notch uplifted by an earthquake in AD 365 (Pirazzoli, 1986) decreases 5 m in elevation over the same 55 km, suggesting that 4 to 5 earthquakes (R.I. ~20 ky) similar to the AD 365 event could account for deformation of the OIS 5a terrace.

The presence of a single notch – biological rim developed at mean low water level since AD 365 west of Mesara bay suggests that the Lefka Ori coastline is stable to slowly subsiding. The discovery of an undated erosional notch decreasing from 4 to 0 m amsl between Lentas and Tsoutsouros (30 km) on the Asterousia coast is evidence for independent footwall uplift between the Lefka Ori and Asterousia blocks. Together, these observations allow for the interpretation of an aseismic subduction thrust and seismic hazards associated with offshore normal faults.