Asperity Size and Neighboring Segments Can Change the Frictional Response and Fault Slip Behavior: Insights From Laboratory Experiments and Numerical Simulations

Accurate assessment of the rate and state friction parameters of rocks is essential for producing realistic earthquake rupture scenarios and, in turn, for seismic hazard analysis. Those parameters can be directly measured on samples, or indirectly based on inversion of coseismic or postseismic slip evolution. However, both direct and indirect approaches require assumptions that might bias the results. Aiming to reduce the potential sources of bias, we take advantage of a downscaled analog model reproducing megathrust earthquakes. We couple the simulated annealing algorithm with quasi-dynamic numerical models to retrieve rate and state parameters reproducing the recurrence time, rupture duration and slip of the analog model, in the ensemble. Then, we focus on how the asperity size and the neighboring segments' properties control the seismic cycle characteristics and the corresponding variability of rate and state parameters. We identify a tradeoff between (a-b) of the asperity and (a-b) of neighboring creeping segments, with multiple parameter combinations that allow mimicking the analog model behavior. Tuning of rate and state parameters is required to fit laboratory experiments with different asperity lengths. Poorly constrained frictional properties of neighboring segments are responsible for uncertainties of (a-b) of the asperity in the order of per mille. Roughly one order of magnitude larger uncertainties derive from asperity size. Those results provide a glimpse of the variability that rate and state friction estimates might have when used as a constraint to model fault slip behavior in nature. We use laboratory experiments and numerical simulations to better understand the seismic behavior of an ideal subduction fault. Although experiments and numerical simulations represent a simplification of nature, they capture the first-order physics of real faults with the advantage of known geometrical and physical properties. This represents a convenient condition for studying fault behavior because observational studies are generally retrieved on several assumptions and poorly constrained parameters (e.g., fault geometry, frictional properties distribution). In this study, we select two of those parameters (i.e., the asperity size and the neighboring segments' frictional properties) and investigate how they control fault behavior. Although we can model the observed slip behavior, we document that even a simple laboratory experiment requires tuning of the friction parameters to reproduce the observables. Rate and state friction parameters of a downscaled, laboratory subduction megathrust are constrainedNumerical models show a tradeoff between (a-b) of the asperity and (a-b) of neighboring segmentsTo fit the behavior of laboratory experiments with different asperity lengths it is necessary to vary (a-b) and Dc