Mitchell, Sam; Sgambato, Claudia; Robertson, Jenni; Roberts, Gerald P; Walker, Joanna P Faure; Mildon, Zoe; Ganas, Athanassios; ... Rugen, Elias J; + view all Mitchell, Sam; Sgambato, Claudia; Robertson, Jenni; Roberts, Gerald P; Walker, Joanna P Faure; Mildon, Zoe; Ganas, Athanassios; Papanikolaou, Ioannis; Iezzi, Francesco; Beck, Joakim; Binnie, Steven A; Dunai, Tibor; Lopez, Damian A; Deligiannakis, Georgios; Mechernich, Silke; Reicherter, Klaus; Rugen, Elias J; - view fewer (2025) Multi-millennia slip rate relationships between closely spaced across-strike faults: Temporal earthquake clustering of the Skinos and Pisia Faults, Greece, from in situ 36Cl cosmogenic exposure dating. Journal of Structural Geology , 198 , Article 105445. 10.1016/j.jsg.2025.105445.

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Abstract

This study investigates slip behaviour on overlapping, en echelon normal faults by analysing the slip histories of the Skinos and Pisia active normal faults over the past ∼20 kyrs using in situ 36Cl cosmogenic dating. New 36Cl data from the Skinos Fault and published Pisia Fault 36Cl data were modelled, with both sample sites located within an overlap zone and separated by an across-strike distance of 1–2 km. Our analysis reveals fluctuating slip rates, with the two faults alternating between out-of-phase and simultaneous slip. The Pisia Fault exhibited a slip rate of ∼0.5–0.75 mm/yr from ∼20 ka to ∼9.6 ka, increasing to ∼1.25 mm/yr until ∼5.2 ka. It then slowed to ∼0.25 mm/yr or less until ∼2.0 ka, before accelerating again to ∼1.25–1.5 mm/yr to the present day. The Skinos Fault maintained a low slip rate of ∼0.25 mm/yr or less from ∼20 ka to ∼6.4 ka, before accelerating to ∼2.0–3.0 mm/yr, persisting to ∼1.0 ka or possibly the present-day. Comparing their slip histories, the faults show periods of simultaneous slip between ∼6.4 ka to ∼5.2 ka and ∼2.0 ka to ∼1.0–0.0 ka, and out-of-phase slip occurred between ∼9.6 ka and ∼6.4 ka, and from ∼5.2 ka to ∼2.0 ka. Out-of-phase behaviour on faults across strike has now been observed on faults spaced across-strike at distances of 1–2 km, 10–20 km, and ∼100 km, raising the question of why it occurs. Possible mechanism(s), including rheological fluctuations within fault/shear-zone structures linked between the brittle upper crust and viscous lower crust and stress interactions, are discussed to explain the out-of-phase and simultaneous slip behaviour.

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