Abstract. Because of the natural (aleatoric) variability in earthquake recurrence
intervals and coseismic displacements on a fault, cumulative slip on a fault
does not increase linearly or perfectly step-wise with time; instead, some
amount of variability in shorter-term slip rates results. Though this
variability could greatly affect the accuracy of neotectonic (i.e., late
Quaternary) and paleoseismic slip rate estimates, these effects have not been
quantified. In this study, idealized faults with four different,
representative, earthquake recurrence distributions are created with equal
mean recurrence intervals (1000 years) and coseismic slip distributions, and
the variability in slip rate estimates over 500- to 100 000-year measurement
windows is calculated for all faults through Monte Carlo simulations. Slip
rates are calculated as net offset divided by elapsed time, as in a typical
neotectonic study. The recurrence distributions used are quasi-periodic,
unclustered and clustered lognormal distributions, and an unclustered
exponential distribution. The results demonstrate that the most important
parameter is the coefficient of variation (CV = standard
deviation ∕ mean) of the recurrence distributions rather than the shape
of the distribution itself. Slip rate variability over short timescales
(< 5000 years or 5 mean earthquake cycles) is quite high, varying by
a factor of 3 or more from the mean, but decreases with time and is close to
stable after ∼40 000 years (40 mean earthquake cycles). This
variability is higher for recurrence distributions with a higher CV. The
natural variability in the slip rate estimates compared to the true value is
then used to estimate the epistemic uncertainty in a single slip rate
measurement (as one would make in a geological study) in the absence of any
measurement uncertainty. This epistemic uncertainty is very high (a factor of
2 or more) for measurement windows of a few mean earthquake cycles (as in a
paleoseismic slip rate estimate), but decreases rapidly to a factor of
1–2 with > 5 mean earthquake cycles (as in a neotectonic slip
rate study). These uncertainties are independent of, and should be propagated
with, uncertainties in fault displacement and geochronologic measurements
used to estimate slip rates. They may then aid in the comparison of slip
rates from different methods or the evaluation of potential slip rate changes
over time.
Late Quaternary slip-rates along the Moxi and Zheduotang segments of the SE Xianshuihe fault, eastern Tibet, and geodynamic implications
