Fractal Spatial Distributions of Initial Shear Stress and Frictional Properties on Faults and Their Impact on Dynamic Earthquake Rupture

Abstract

We investigate the influence of the heterogeneous slip-weakening distance ( D-C ) in dynamic rupture simulations, in which D-C is proportional to the fault irregularities. Specifically, we compare a heterogeneous fractal D-C distribution to a uniform D-C over the entire fault when the initial shear stress is also heterogeneous. We find that even small changes in the average value of D-C ( < 1 mm) can lead to significant differences in the rupture evolution; that is, the average D-C and the way D(C )is distributed determines if the rupture is a runaway, self-arrested, or nonpropagating. We find that the self-arrested ruptures differ from runaway ruptures in the amount of area characterized by large slips (asperities). Self-arrested ruptures match the Somerville et al. (1999) asperity criteria in which – 25% of ruptured area radiate – 45% of the total seismic moment. This criterion is not satisfied for runaway ruptures. For runaway ruptures, – 50% of the ruptured area radiates about 70% of the seismic moment, indicating that the ruptured area is not linearly proportional to the seismic moment. Self-arrested ruptures are characterized by dynamic shear stress drops (SDs) in the range – 2.9 -5.5 MPa, whereas for runaway ruptures the dynamic SDs increase to values between -12 and 20 MPa. Self-arrested ruptures generated by fractal distributed D-C resemble the rupture properties of observed earthquakes. In addition, results show that the conditions for self-arrested ruptures are connected to the decrease of residual energy at rupture boundaries.