Paleoseismological investigation of the oblique-normal Ekkara ground rupture zone accompanying the M 6.7-7.0 earthquake on 30 April 1954 in Thessaly, Greece: Archaeological and geochronological constraints on ground rupture recurrence

Observations in trenches excavated across the Ekkara rupture zone (ERZ), the longest of the sporadic ground ruptures that accompanied the M 6.7-7.0 earthquake of 30 April 1954 on the Domokos fault zone (DFZ), identify a left-lateral oblique-normal fault with a slip vector aligned with the regional extension direction (verifying the tectonic origin of the ERZ). The paleoseismological interpretation of stratigraphic, soil-stratigraphic, and tectonic features is discussed with emphasis on the issues related to strongly oblique fault kinematics. Two pre-1954 events of ground rupture are recognized (E1 and E2) and an event of ground cracking only (E1a, shortly after E1). Event E2 was accompanied by larger displacement than E1 and 1954, but this does not necessarily imply a stronger earthquake. Archaeological dating of transported ceramic sherds constrains E1 between 6750 and 4450 B. P. (more likely, 6450-5750 B.P.). Luminescence dating of colluvial deposits and C-14 dating of pedogenic carbonates (stone coatings) place E2 at similar to 17,500 +- similar to 2500 B.P. (preferred age). In the (hazard-wise) most conservative interpretation, recent recurrence intervals of ERZ activations exceed 3195 years. The sporadic nature of the 1954 ruptures precludes certainty on whether the ERZ has recorded every past activation of the DFZ unless data are also collected from other DFZ rupture zones. Minimum-limiting estimates of 0.3-0.5 mm/yr slip rate are derived for the ERZ, and the true slip rate is not expected to exceed 1 mm/yr. Slip rate estimates for the ERZ may be minima for the DFZ slip rate, however, because coseismic deformation in the past may have been distributed to more than one rupture zones at the surface.