Temporal and spatial earthquake clustering revealed through comparison of millennial strain-rates from 36Cl cosmogenic exposure dating and decadal GPS strain-rate

Abstract
To assess whether continental extension and seismic hazard are spatially-localized on single faults or spread over wide regions containing multiple active faults, we investigated temporal and spatial slip-rate variability over many millennia using in-situ Cl cosmogenic exposure dating for active normal faults near Athens, Greece. We study a ~ NNE-SSW transect, sub-parallel to the extensional strain direction, constrained by two permanent GPS stations located at each end of the transect and arranged normal to the fault strikes. We sampled 3 of the 7 seven normal faults that exist between the GPS sites for Cl analyses. Results from Bayesian inference of the measured Cl data implies that some faults slip relatively-rapidly for a few millennia accompanied by relative quiescence on faults across strike, defining out-of-phase fault activity. Assuming that the decadal strain-rate derived from GPS applies over many millennia, slip on a single fault can accommodate ~ 30–75% of the regional strain-rate for a few millennia. Our results imply that only a fraction of the total number of Holocene active faults slip over timescales of a few millennia, so continental deformation and seismic hazard are localized on specific faults and over a length-scale shorter than the spacing of the present GPS network over this time-scale. Thus, (1) the identification of clustered fault activity is vital for probabilistic seismic hazard assessments, and (2) a combination of dense geodetic observations and palaeoseismology is needed to identify the precise location and width of actively deforming zones over specific time periods.

Citation
Iezzi, F., Roberts, G., Faure Walker, J., Papanikolaou, I., Ganas, A., Deligiannakis, G., … Gheorghiu, D. (2021). Temporal and spatial earthquake clustering revealed through comparison of millennial strain-rates from 36Cl cosmogenic exposure dating and decadal GPS strain-rate. Scientific Reports, 11(1). doi:10.1038/s41598-021-02131-3

Acknowledgements
Tis work has been funded by NERC Grant CIAF 9183-1017, NERC Studentship NE/L002485/1, MIS 5002697/NSRF 2014-2020, Greece, and the European Union (European Regional Development Fund). A.G acknowledges funding by the project “HELPOS—Hellenic System for Lithosphere Monitoring”. We thank the Editor Antonio Avallone and three anonymous reviewers for the comments and suggestions that have improved the paper.

Publisher
Springer Science and Business Media LLC

Journal
Scientific Reports

DOI
10.1038/s41598-021-02131-3

Additional Links
https://www.nature.com/articles/s41598-021-02131-3

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