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Determining reliable histories of slip on normal faults with bedrock scarps using cosmogenic exposure data
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  • H J Goodall,
  • Laura Gregory,
  • L N J Wedmore,
  • K J W Mccaffrey,
  • R M J Amey,
  • G P Roberts,
  • R P Shanks,
  • R J Phillips,
  • A Hooper
H J Goodall
University of Leeds
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Laura Gregory
University of Leeds

Corresponding Author:[email protected]

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L N J Wedmore
University of Bristol
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K J W Mccaffrey
Durham University
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R M J Amey
University of Leeds
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G P Roberts
Birkbeck, University of London
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R P Shanks
SUERC, University of Glasgow
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R J Phillips
University of Leeds
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A Hooper
University of Leeds
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Abstract

Cosmogenic exposure data can be used to calculate time-varying fault slip rates on normal faults with exposed bedrock scarps. However, the method relies on assumptions related to how the scarp is preserved, which should be consistent at multiple locations along the same fault. Previous work commonly relied on cosmogenic data from a single sample locality to determine the slip rate of a fault. Here we show that by applying strict sampling criteria and using geologically informed modelling parameters in a Bayesian-inference Markov chain Monte Carlo method, similar patterns of slip rate changes can be modelled at multiple sites on the same fault. Consequently, cosmogenic data can be used to resolve along-strike fault activity. We present cosmogenic 36Cl concentrations from seven sites on two faults in the Italian Apennines. The average slip rate varies between sites on the Campo Felice Fault (0.84 0.23 to 1.61 0.27 mm yr ^-1), and all sites experienced a period of higher than average slip rate between 0.5 and 2 ky and a period of lower than average slip rate before 3 ky. On the Roccapreturo fault, slip rate in the centre of the fault is 0.550.11 and 0.350.05 mm yr ^-1 at the fault tip near a relay. The estimated time since the last earthquake is the same at each site along the same fault. These results highlight the potential for cosmogenic exposure data to reveal the detailed millennial history of earthquake slip on active normal faults.