17 Jul 2023
 | 17 Jul 2023

Paleoearthquake reconstruction on an impure limestone fault scarp at Sparta, Greece

Bradley Goodfellow, Marc Caffee, Greg Chmiel, Ruben Fritzon, Alasdair Skelton, and Arjen Stroeven

Abstract. Reliable reconstructions of paleoseismicity are useful for understanding, and mitigating, seismic hazard risks. In this study, we apply cosmogenic 36Cl exposure-age dating and concentrations of rare-earth elements and yttrium (REY) to unravelling the paleoseismic history of the Sparta fault, Greece, which is a range-bounding normal fault developed in limestone. Modeling of 36Cl concentrations along two vertical profiles on the Sparta Fault indicates a clustering of four earthquakes within a 1.5 kyr period that culminated with the 464 B.C.E. event that devastated Spartan society. Cumulative uplift was as high as 2.8 mm yr-1 during that period, compared with ~0.6–0.9 mm a-1 over the preceding 2.7–4.4 kyr. Because earthquake activity may shift between faults in extensional settings, a large magnitude earthquake is not necessarily indicated as being overdue by the present ~2.5 kyr quiescent period. More generally, accurate identification of individual earthquakes is presently constrained by spatial variations in 36Cl concentration profiles that reflect neither exposure duration nor imprints of former soil profiles. In cases where this is attributable to mineralogical variations, such as in the Sparta fault scarp, present chemical preparation techniques for AMS measurement of 36Cl may insufficiently account for those variations.

The Sparta fault scarp is composed of fault breccia, which contains quartz and clay-lined pores, in addition to host rock-derived clasts of calcite and microcrystalline calcite cement. The exchange of REY between the hanging wall colluvium and the fault scarp calcite, which has been applied to the study of paleoseismicity on other limestone normal faults, is overwhelmed on this fault scarp by REY attached to the breccia pore clays. Holocene earthquakes and their magnitudes, inferred from fault slip lengths, therefore cannot be inferred from REY data for impure limestone faults such as the Sparta fault but, rather, these data may indicate processes of fault evolution in the Earth’s near surface.

Bradley Goodfellow et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-1585', Anonymous Referee #1, 13 Aug 2023
    • AC1: 'Reply on RC1', Arjen Stroeven, 05 Nov 2023
  • RC2: 'Comment on egusphere-2023-1585', Anonymous Referee #2, 01 Sep 2023
    • AC2: 'Reply on RC2', Arjen Stroeven, 05 Nov 2023
  • RC3: 'Comment on egusphere-2023-1585', Anonymous Referee #3, 30 Sep 2023
    • AC3: 'Reply on RC3', Arjen Stroeven, 05 Nov 2023
  • EC1: 'Editor Comment on egusphere-2023-1585', Federico Rossetti, 11 Oct 2023
    • AC4: 'Reply on EC1', Arjen Stroeven, 07 Nov 2023

Bradley Goodfellow et al.

Bradley Goodfellow et al.


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Short summary
Reconstructions of past earthquakes are useful for assessing earthquake hazard risks. We dated a limestone scarp that has been exposed by earthquakes along the Sparta fault, Greece. From this we identify a cluster of four earthquakes within a 1500 year period that culminated with the 464 B.C. event that devastated Spartan society. However, a large earthquake is not necessarily indicated as being overdue by the present ~2500 year period of inactivity on the Sparta fault.