Long-term versus short-term deformation of the meizoseismal area of the 2008 Achaia–Elia (MW 6.4) earthquake in NW Peloponnese, Greece: Evidence from historical triangulation and morphotectonic data

Abstract

The deformation of the meizoseismal area of the 2008 Achaia–Elia (MW 6.4) earthquake in NW Peloponnese, of the first significant strike slip earthquake in continental Greece, was examined in two time scales; of 102years, based on the analysis of high-accuracy historical triangulation data describing shear, and of 105–106years, based on the analysis of the hydrographic network of the area for signs of streams offset by faulting. Our study revealed pre-seismic accumulation of shear strain of the order of 0.2μrad/year in the study area, consistent with recent GPS evidence, but no signs of significant strike slip-induced offsets in the hydrographic network. These results confirm the hypothesis that the 2008 fault, which did not reached the surface and was not associated with significant seismic ground deformation, probably because of a surface flysch layer filtering high-strain events, was associated with an immature or a dormant, recently activated fault. This fault, about 150km long and discordant to the morphotectonic trends of the area, seems first, to contain segments which have progressively reactivated in a specific direction in the last 20years, reminiscent of the North Anatolian Fault, and second, to limit an 150km wide (recent?) shear zone in the internal part of the arc, in a region mostly dominated by thrust faulting and strong destructive earthquakes.