Date: 25 October (Thursday)
Time: 10:30 – 12:00
Room: C200 at the New Building of Research Center for Earthquake Prediction

Speaker: Jianye Chen (Utrecht University)

*Presentation Title:* *Microphysical model predicts the limit to fault re-strengthening: logarithmic vs. power-law healing*
*Abstract:* The maximum fault strength and rate of interseismic fault strengthening (‘healing’) are of primary interest to earthquake hazard assessment studies, as they directly relate to event magnitude and recurrence time. Previous laboratory studies have revealed two distinct frictional healing behaviors, referred to as Dieterich-type and non-Dieterich-type healing. These are characterized by, respectively, loglinear and power-law increase in the strength change with time. To date, there is no physical explanation for the frictional behavior of fault gouges that unifies these observations. Using a microphysical friction model recently developed for granular fault gouges, we investigate fault strengthening analytically and numerically under boundary conditions corresponding to laboratory slide-hold-slide tests. We find that both types of healing can be explained by considering the difference in grain contact creep rheology at short- and long time-scales. In other words, they are UNIFIED by the same model. We derive physically meaningful, analytical expressions for frictional healing parameters (e.g. frictional healing rate, intrinsic cutoff time, maximum healing), of which the predictions are consistent with the numerical implementation of the model. On this basis, we interpret the re-strengthening of seismogenic faults during seismic cycles.

*Presenter introduction*: Jianye Chen is a post-doctoral researcher from the High Pressure and Temperature laboratory of Utrecht University, the Netherlands. During his Ph.D. he improved the understanding of destructive seismicity in limestone terrains by performing laboratory friction and fluid-flow experiments (with a case study of the Longmenshan Fault which hosted devastating Mw7.9 Wenchuan Earthquake, China). During and since his Ph.D., he developed a general microphysical model for friction of granular material (e.g. fault gouges), providing insight into the microphysical mechanisms that control fault slip instabilities, and how these mechanisms scale to natural faults. The new model has been successfully applied to explain a wide spectrum of fault behavior observed in both laboratory and in nature.