Increasing fault slip rates within the Corinth Rift, Greece: a rapidly localising active rift fault network

Abstract

As a young (<5 Myr old) active rift with high resolution spatial and temporal constraints, the Corinth Rift is a natural laboratory for testing models of rift and fault network development in the early stages of continental rifting. New analyses of the rift fault network in the offshore syn-rift sequence are combined with ocean drilling borehole data from IODP Expedition 381. The expedition drilled and sampled syn-rift sediments from the last few Myr and provides the first absolute age framework for the offshore rift, allowing determination of robust fault slip rates and temporal patterns in fault network activity. Spatial variations in activity and rates throughout the rift fault network, for four time intervals over the past ∼2 Myr, illustrate changes in strain distribution and highlight three dominant processes controlling the development of the fault network: 1) progressive strain localisation and transfer of strain from major S-dipping to major N-dipping faults from ∼2 Ma – 130 ka; 2) linkage of a southern border fault system and subsequent acceleration of fault slip rates on major N-dipping faults at ∼335 ka; 3) increased rift margin flexure and subsequent deformation since ∼130 ka, a response to rapid subsidence in the hanging wall of an established crustal scale border fault system. Since ∼130 ka the rift fault network has experienced a two-fold increase in average cumulative slip rates, with the highest slip rates (>7 mm/yr) occurring on major segments of the border fault system in the central rift. A comparison of seismic moment rates from historical earthquakes (last 320 years) is consistent with the geological timescale of fault slip rates (highest rates in the western and central rift), but not with the distribution of very recent activity (from 50-year earthquake records). As a result, a moment deficit is present along the central rift, which could be accommodated by a large (Mw 6.5) earthquake, potentially even rupturing multiple linked fault segments. The details of rift fault network activity from this study reveal how quickly strain can migrate and become localised during early continental rifting, and how rapidly fault slip accelerates in response to the establishment of major rift border fault systems. Identifying the nature and timescales of these important rift processes furthers our models of early rift evolution and has implications for assessing seismic hazard in regions of active continental rifting.

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