Detection of active fault scarps in western Peloponnese, Greece

Abstract

This study aims at reconstructing Pleistocene slope erosion processes and transformation of relief in well-developed Pleistocene (Tyrrhenian) marine terraces along the western Peloponnese. The investigations are based on existing geological data, field observations, a selected seismic reflection profile, sedimentological analysis and radiometric dating.Aftershock rupture segment extends for 6 km in a WNW direction. Each fault movement in an earthquake results in a sudden increase in the size of the scarp, by an amount ranging from a few centimeters to several meters.Thrust faulting occurs on shallow dipping faults and does not commonly produce a true fault scarp, because the tip of the upper part, over the thrust block, tends to collapse, leaving a sinuous scarp that does not coincide with the fault plane. Strike-slip faulting may result in a scarp if there is a significant extensional or thrust component of motion, or if rock-types with different weathering characteristics and thickness are compared by faulting. Failing this, both active and inactive faults are often marked by a fault-line, a line of preferential erosion along the fault. The combined effects of fault motion, erosion, and sediment deposition affect the form of the scarp and the latter two will eventually eliminate it after movement on the fault ceases. If the rock erosion rates on both fault sides are known or can be assumed to be negligible, and the sediments deposited contain material that can be dated, then the magnitude of the scarp can be used to determine the age at which the scarp began to form and the long-term rate of movement on the fault. More information regarding the relative significance and rate of movement of these faults can be obtained by observing their effects on the drainage pattern in the area.In particular, morphotectonic data indicate that the observed rupture segment may reflect a fault-line scarp corresponding to an old fault scarp, which belongs to the isotopic stage 7 or prior, i.e. isotopic stage 11, during the evolution of NW Peloponnese basin.Moreover, morphotectonic data clearly shows that NW Peloponnese is characterized by a complex structural pattern and erosion process phenomena aided by human activity. This data is well-supported by seismic reflection profiles information.