Lithospheric flexure and rheology determined by climate cycle markers in the Corinth Rift

Abstract

Geomorphic strain markers accumulating the effects of many earthquake cycles help to constrain the mechanical behaviour of continental rift systems as well as the related seismic hazards. In the Corinth Rift (Greece), the unique record of onshore and offshore markers of Pleistocene ~100-ka climate cycles provides an outstanding possibility to constrain rift mechanics over a range of timescales. Here we use high-resolution topography to analyse the 3D geometry of a sequence of Pleistocene emerged marine terraces associated with flexural rift-flank uplift. We integrate this onshore dataset with offshore seismic data to provide a synoptic view of the flexural deformation across the rift. This allows us to derive an average slip rate of 4.5-9.0 mm·yr-1 on the master fault over the past ~610 ka and an uplift/subsidence ratio of 1:1.1-2.4. We reproduce the observed flexure patterns, using 3 and 5-layered lithospheric scale finite element models. Modelling results imply that the observed elastic flexure is produced by coseismic slip along 40-60° planar normal faults in the elastic upper crust, followed by postseismic viscous relaxation occurring within the basal lower crust or upper mantle. We suggest that such a mechanism may typify rapid localised extension of continental lithosphere.

Geometry of Flexural Uplift by Continental Rifting in Corinth, Greece

“…Markers show the growth of ~4.8 km of structural relief since the onset of bounding fault activity, 800–600 ka, which localized strain over a ~300‐kyr interval (Nixon et al, ). Flexural uplift on 10 4 –10 6 ‐year time scales is recorded by the Late Pleistocene marine terraces (Figures and ; Armijo et al, ; De Gelder et al, ). If a similar signal of flexural uplift also exists westward, it should be recorded in geomorphological evidence along the rift margin.…”

“…Onshore‐offshore cross section showing elastic flexure as detailed by coeval markers of sea level and river profiles rescaled to fit the section located in Figure . Paleohorizons in different colors represent major sea level highstands (see inset in the bottom left) that have been derived from best fit quadratic curves of upflexed terraces in the onshore (De Gelder et al, ) and their tentatively correlatable seismic horizons in the offshore (Nixon et al, ) on the seismic line L35 of Taylor et al (), depth‐converted as in de Gelder et al (). Modified after Figure 3 of de Gelder et al ().…”

“…In the east rift, elastic flexure on the main fault flanks sets the modern asymmetry (Figure ). An extensive sequence of exceptionally preserved marine terraces in the eastern footwall (Armijo et al, ), and prominent syntectonic sedimentary wedges of correlatable seismic horizons in its hanging‐wall (Taylor et al, ) record an exponential increase in elastic flexure amplitude toward the rift bounding fault (Figure ; De Gelder et al, ). Markers show the growth of ~4.8 km of structural relief since the onset of bounding fault activity, 800–600 ka, which localized strain over a ~300‐kyr interval (Nixon et al, ).…”

“…Up‐warping in continental rift margins and footwalls is particularly interesting, for the upflexed topography can be used to discriminate between low‐ and high‐angle extensional faulting (Bell et al, ). Similarly, the wavelength and curvature of flexural uplift can be used to infer relative strength layering of the underlying lithosphere (e.g., Armijo et al, ; De Gelder et al, ). These and other inferences on lithosphere strain, mechanics, and rheology are nevertheless limited to the spatiotemporal scale and overall detail at which flexure is characterized in nature.…”

“…Research in these areas uses flexure geometries derived from relatively imprecise observations of topography to deduce rift mechanics and/or geodynamics (e.g., Brown & Phillips, ; Masek et al, ; Owens, ; ter Voorde et al, ; Zandt & Owens, ). Finer characterizations of flexure geometry that may lead to better‐constrained results are either precluded by scant unambiguous geomorphological evidence in relatively old (>10 6 years) regions (e.g., Stein et al, ) or restricted to individual transects (Armijo et al, ; De Gelder et al, ) and/or short temporal scales (<10 3 years; e.g., Thompson & Parsons, ).…”