Deformation On Parallel Fault Strands Associated With The Fault Tip Zone Of The South Alkyonides Normal Fault, Greece, Quantified Using Combined 36Cl Exposure Dating Of Wave-Cut Platforms, 234U/230Th Coral Dating, And Detailed Mapping.

Complex fault geometry is frequently observed within the tip zones of propagating normal faults, and tends to be characterized by small length-scale faults, relative to the main fault, with across-strike distances between rupture surfaces of meters to tens of meters. Detailed analysis of the distributed faulting within a tip zone can be used to quantitatively explore 'off fault' deformation in order to establish how this varies relative to 'on fault' deformation and, importantly, contribute to seismic hazard analyses.

We examine a set of distributed, closely-spaced normal faults situated on the Perachora Peninsula, located in the western fault tip zone of the South Alkyonides Fault (SAF), a crustal-scale normal fault in the actively extending Gulf of Corinth, Greece. We have dated five wave-cut platforms at elevations of 29 m, 42 m, 46 m, 60 m, and 62 m using in-situ ³⁶Cl cosmogenic exposure dating and use these alongside ²³⁴U/²³⁰Th coral ages and our detailed field mapping to suggest that the entire western part of the Perachora Peninsula was initially formed as a single wave-cut platform during the 125 ka sea-level highstand. This surface is now intersected by at least 30 E-W and N-S trending normal faults and consequently occurs at varying elevations between 7-90 m.

Knowledge of the original age of the surface in combination with our field mapping is used to calculate summed throw rates of between 0.3 mm/yr and 0.6 mm/yr and maximum summed fault-related uplift values of 0.46 mm/yr since 125 ka. These values are comparable to the 'on fault' uplift values for the SAF of between 0.28 mm/yr - 0.64 mm/yr reported in the literature, which implies that areas of complex distributed faulting can result in time-averaged deformation values similar to those observed along localized fault sections.

While the fault lengths within these distributed zones are smaller compared to the main faults, perhaps implying low earthquake magnitudes, we show that this tip zone was probably ruptured in the large magnitude 1981 Mw 6.7-6.9 sequence, and perhaps in previous earthquakes; they may still pose a significant seismic hazard. We discuss tip zones in terms of seismic hazard assessment.