Determining reliable histories of slip on normal faults with bedrock
scarps using cosmogenic exposure data
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.