Modelling precursory laboratory seismicity using a roughness-based rate-
and state-dependent friction model
Abstract
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. Surface
profilometry of the fault surface taken \textit{a
posteriori} 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 $\delta$, seismic moment $M_{0}$, stress drop
$\Delta \tau$ and fracture energy
$G^{’}$, 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.