Simulated Rupture Dynamics and Radiated Energy on Heterogeneously Damaged Faults.

Rupture dynamics along a heterogeneous fault is studied in the framework of the recently developed damage‐breakage rheological model. The model utilizes a fault structure accommodating shear and wear in a heterogeneous weak fault‐core a few centimeters thick, separating two blocks with damage level gradually decreasing toward the host rock. We first demonstrate the similarity of the static stress field around a fault, represented by a three‐body tribosystem, to the one developed around a rough frictional interface. We show that both models predict heterogeneous stress field pattern. We then apply simulations of rupture on heterogeneously damaged faults. We show that increasing initial heterogeneity amplitudes is associated with smaller events with lower slip rates. The simulations further allow us to quantify the amount of accumulated damage correlative with wearing. During the propagating rupture, the strength of the fault‐core evolves, leading to higher wear generation along relatively strong zones or barriers. The total wear production in a given event is strongly dominated by the initial damage heterogeneity. Processing of synthetic seismograms shows excess energy radiation of high‐frequency seismic waves comparing to the expected radiation from planar faults. This radiation is enhanced with the increase in the variability of fault strength heterogeneity. Further calculations of the scaled energy show good fit with previous seismological and laboratory observations and demonstrate the impact of fault heterogeneity on radiated energy during dynamic rupture. Therefore, initial fault heterogeneity, manifested by fault‐core strength or by geometrical irregularity controls many aspects of earthquake rupture, including slip displacement and velocity. Plain Language Summary: Earthquakes are triggered when the stress build‐up on rocks exceeds the resistance to fracture of fault material. When faulting occurs, energy is generated in the fault zone and radiated through the rock body to the surface. The ground motions and their durations strongly depend on the earthquake rupture characteristics such as the amount of displacement, velocity, and directivity. Many studies modeled natural faults as planar frictional interfaces that failed and were displaced during earthquakes. Yet, geological observations and seismological measurements demonstrated that this is probably a naive picture, and fault zones are very heterogeneous, including complicated geometry and variation of strength along and across them. Here we examine the effect of such initial heterogeneities on earthquake and show that the heterogeneity of the rock strength in the fault core itself strongly affects earthquake dynamics. In particular, larger magnitude earthquakes are predicted for the more homogenous fault. We also find that higher fault heterogeneity would result in excess high‐frequency radiation. Considering these effects on ground motion around the fault, we show that seismological records may capture these differences in fault characteristics during earthquakes. Key Points: Initial damage level and its heterogeneity along the fault core control dynamics and seismic moment of simulated rupture eventsWear production is affected by the initial damage distribution. During slip, higher wear accumulation is calculated for barriers along faultsHigh variability of fault damage heterogeneity significantly enhances high‐frequency radiation [ABSTRACT FROM AUTHOR]