The seismic history of the Pisia fault (eastern Corinth rift, Greece) from fault plane weathering features and cosmogenic 36Cl dating

Abstract

The deformation of the eastern Corinth rift (Greece) is distributed along several E-W trending active normal faults. Here, the 25-km-long Pisia fault experienced up to 150 cm of coseismic displacement during the 1981 Alkyonides earthquake sequence (M = 6.7, 6.4, 6.3). Using terrestrial laser scanning, coupled with analyses of color changes, lichen colonization and karstic features, we identify differentially weathered horizontal stripes on the exposed Pisia fault plane. The stripe boundaries occur at scarp heights of 1.10 m, 2.05 m, 2.85 m, 3.60 m, 4.15 m, and 5.15 m, with two additional possible boundaries at 3.10 m and 4.65 m (ca. ± 0.1 m respectively). This indicates that six to eight paleoearthquakes have exhumed the fault plane in a series of distinct coseismic slip events. A vertical profile of cosmogenic 36Cl measurements is used to constrain age models of the exhumation. The results imply that, in addition to the last earthquake of 1981 (EQ1), exhumation events occurred at ~2.0 kyr (EQ2), ~3.1 kyr (EQ3), ~4.5 kyr (EQ4/4a,b), ~6.0 kyr (EQ5), and ~7.3 kyr (EQ6/6a,b), with modeled age uncertainties of ~0.7 kyr. Bayesian modeling provides a mid and late Holocene slip rate of 0.5-0.6 mm/yr (last 7.3 ± 0.7 kyr), while the upper part of the 8.45-m-high fault plane was exhumed at a higher rate of 0.8-2.3 mm/yr (7.3 ± 0.7 kyr to 10.2 ± 1.9 kyr). This slip rate variability suggests an increased seismicity or larger slip events during the early Holocene.

Distributed normal faulting in the tip zone of the South Alkyonides Fault System, Gulf of Corinth, constrained using 36Cl exposure dating of Late-Quaternary wave-cut platforms.

“…Specifically, analysis of post-LGM slip on the Pisia fault revealed maximum slip rates of 2.3 mm/yr during the Holocene (Mechernich et al, 2018). Palaeoseismic trenching along the Skinos fault yielded throw rates of 1.2-2.5 mm/yr over ~1500 years (Collier et al, 1998).…”

Displacement Accumulation and Sampling of Paleoearthquakes on Active Normal Faults of Crete in the Eastern Mediterranean

“…The age of active fault scarps in Greece and western Turkey is primarily constrained by cosmogenic dating which suggests that climatic conditions were favorable for scarp formation from 16.5 ± 2 ka to the present day (Benedetti et al., 2003, 2013; Mechernich et al., 2018; Mouslopoulou et al., 2014; Mozafari et al., 2019). Historical earthquakes in the Mediterranean region support the interpretation that the majority of slip recorded by limestone fault scarps accrues during earthquakes (Benedetti et al., 2003, 2013; Mechernich et al., 2018; Mozafari et al., 2019). The earthquake‐slip model for scarp formation in Crete is also consistent with observations from cultural strain markers (e.g., roads and fences) constructed last century that show no evidence of creep on active faults at the ground surface (this study).…”

Evaluating variability in coseismic slips of paleo-earthquakes from an incomplete slip history: an example from displaced terrace flights across the Kamishiro fault, central Japan

“…(e.g., McCalpin, 2009), geological records significantly contribute to examining whether there is a certain regularity of recurrence intervals and magnitudes of large earthquakes (e.g., Shimazaki and Nakata, 1980;Schwartz and Coppersmith, 1984;Grant, 1996;Weldon et al, 2004;Zielke et al, 2015). Although many studies have presented evidence that faults appear to behave regularly with regard to the size and recurrence intervals of large earthquakes (e.g., Klinger et al, 2011;Berryman et al, 2012), others have reported fluctuations (e.g., Chen et al, 2007;Schlagenhauf et al, 2011;Rockwell et al, 2015;Komori et al, 2017;Scharer et al, 2017;Mechernich et al, 2018;Wechsler et al, 2018). This raises the question of how variable earthquake recurrences are in terms of their size and recurrence interval.…”