Validation of seismic source properties using rate and state-dependent friction models of frictional acoustic emissions

Recent seismic observations show that faults experience a range of slip patterns spanning many scales in both space and time. Understanding how slip accumulates on complex fault systems can lead to a better understanding of regions that are more prone and susceptible to large events.We investigate experimental results from a direct shear friction apparatus, where a fault was formed by pressing mature, worn surfaces of two polymethyl methacrylate (PMMA) samples on top of each other in a dry environment. The fault was sheared until macroscopic stick-slip frictional failure occurred. Before the macro-failure small precursory seismicity nucleated from regions that also experienced aseismic slow slip. These precursory events did not cascade-up into gross fault rupture and arrested locally. Reasons as to why ruptures arrested are investigated using a 1-D rate and state friction (RSF) model. Fault surface geometry taken a posterior revealed wear in the form of a bimodal Gaussian distribution of surface height. In our model, this unique distribution of surface roughness is determined to be a proxy for the heterogeneous spatial description of the critical slip distance D_c. We assume that smooth (polished) sections of fault exhibited lower D_c than rougher sections of the bimodal Gaussian roughness profile. We used a quasi-dynamic RSF model that determined localized seismicity initiated at the smooth sections. Source properties: average slip δ, seismic moment M₀, stress drop Δσ and fracture energy G_c, were determined for each event. We compare the numerically modeled source properties to experimental source characteristics inferred from seismological estimates using an array of acoustic emission sensors from a concerted study. We discuss similarities, discrepancies and assumptions between these two independent models (kinematic and dynamic) used to study earthquakes for the first time in the laboratory. We found that complexity formed by fault roughness could produce a wide range of slip behaviours that are also observed in natural systems at many scales. Understanding how roughness evolves over a fault's lifetime will be important for moving forward earthquake science.