Microphysically-based modelling of earthquake cycles incorporating seismic and aseismic slip

Earthquake hazard studies benefit from an advanced capability to simulate earthquake cycles based on models that are consistent with laboratory observations. Such modelling provides a basis to integrate geodetic and seismological observations of fault slip into a quantitative mapping of fault properties, ultimately leading to an improved predictability of fault behaviour. Currently, rate-and-state friction (RSF) is most commonly used for the characterisation of laboratory friction experiments. However, the RSF framework provides little physical basis for the extrapolation of these results to the scales and conditions of natural faults, leaving questions regarding the applicability of the RSF parameters for predicting seismic cycle transients. As an alternative to RSF, microphysically-based models offer means for interpreting laboratory and field observations, but are generally over-simplified with respect to heterogeneous natural systems. In order to bridge the temporal and spatial gap between the laboratory and nature, we have implemented existing microphysical model formulations into an earthquake cycle simulator. This enables the study of natural seismic cycles by explicitly taking into account the interaction between e.g. fault gouge composition, temperature, and stress. We demonstrate the utility of this model by considering a compositionally heterogeneous fault zone, under conditions that facilitate earthquake nucleation. These simulations reveal the existence of two distinct types of earthquakes. The first class of earthquakes comprises relatively small seismic events that occur quasi-randomly in time and space. By contrast, the second class of earthquakes comprises fault-spanning events that may be analogous to real-world Mw > 8 events. Notably, these anomalously large events are time-predictable on the basis of fault stress. Thus, the microphysically-based approach offers new opportunities for investigating the long-term seismic cycle behaviour of natural faults, and to improve seismic hazard assessments.