Localisation of Quaternary Slip-Rates In An Active Rift In 100,000 Years Constrained by 234U-230Th Coral Dates from Uplifted Palaeoshorelines, Central Greece: Reconciling Geologic and Geodetic Deformation Rates

Mapping, dating and modeling of palaeoshorelines uplifted in the footwall of the 1981 Gulf of Corinth earthquake fault, Greece (Ms 6.9-6.7), are used to (1) assess its slip-rate history relative other normal faults in the area, (2) study strain localization, (3) reconcile geologic and geodetic rates of extension. 234U-230Th coral ages from Cladocora caespitosa date uplifted shoreface sediments and palaeoshorelines from glacio-eustatic sea-level highstands at 76 ka, possibly 100 ka, 125 ka, 175 ka, 200 ka, 216 ka, 240 ka and 340 ka. Uplifted Quaternary and Holocene palaeoshorelines decrease in elevation towards the western tip of the fault, exhibiting larger tilt angles with age, showing that uplift is due to progressive fault slip. Since 125 ka, uplift rates varied from 0.25 mm/yr to 0.52 mm/yr over a distance of 5 km away from the fault tip. Tilting was also occurring prior to 125 ka, but uplift rates were lower because the 125 ka palaeoshoreline is at 77% of the elevation of the 240 ka palaeoshoreline despite being nearly half its age. Comparison of palaeoshoreline elevations and sedimentology with the Quaternary sea-level curve show that slip-rates increased by a factor of 3.2 ± 0.2 at 175 ± 75 ka, synchronous with cessation of activity on a neighbouring normal fault at 382-112 ka. We suggest that the rapid extension rates of up to 10-15 mm/yr across the Gulf of Corinth measured with GPS formed following displacement localization as one set of faults accelerated to accommodate the cessation of slip on another set. Thus, fault interaction controls the spatial variation in deformation rates that are set by larger scale processes responsible for the extension. GPS rates apply only since 175 ± 75 ka and this should be included in models of lithospheric extension derived from velocity field determinations.