Temporal and spatial earthquake clustering revealed through comparison of millennial strain-rates from
36Cl cosmogenic exposure dating and decadal GPS strain-rate.
Sci Rep 2021;
11:23320. [PMID:
34857777 PMCID:
PMC8639784 DOI:
10.1038/s41598-021-02131-3]
[Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 10/29/2021] [Indexed: 11/16/2022] Open
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 36Cl 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 36Cl analyses. Results from Bayesian inference of the measured 36Cl 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.
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