Earthquake cycles on a self-similar rough fault: The importance of the minimum roughness wavelength

Elias R. Heimisson

Published August 9, 2019, SCEC Contribution #9412, 2019 SCEC Annual Meeting Poster #170

Faults in nature demonstrate fluctuations from planarity at most length scales that are relevant for earthquake dynamics. These fluctuations may influence all stages of the seismic cycle; earthquake nucleation, propagation, arrest, and inter-seismic behavior. Here I show quasi-dynamic plane-strain simulations of earthquake cycles on a self-similar 10 km long rough fault. The minimum roughness wavelength and nucleation length scales are well resolved and much smaller than the fault length. Stress dissipation is implemented using a variation of the back-slip approach, which allows for efficient simulations of multiple cycles without stresses becoming unrealistically large. I explore varying the minimum roughness wavelength, for the same stochastically generated realization of a rough fault. The minimum roughness wavelengths explored are from 1/3 to 10 times the nucleation length for a planar fault. This exploration reveals how the minimum roughness wavelength plays an important role in changing the characteristics of the fault seismicity and rupture behavior. Decreasing the minimum roughness wavelength causes the minimum and maximum earthquakes sizes to decrease. Thus the fault seismicity is characterized by smaller and more numerous earthquakes, on the other hand, increasing the minimum roughness wavelength results in fewer and larger events. However, in all cases, the inferred b-value is constant. Characteristics of individual ruptures are also altered. Seismic events are initially crack-like, but at a critical length scale, they continue to propagate as pulses, locking in an approximately spatially fixed amount of slip. I investigate this transition using simple scaling arguments and show how a characteristic pulse length and slip distance arise from roughness drag. The results suggest that the ratio of minimum roughness wavelength to the squared amplitude-to-wavelength ratio may be approximately estimated from dynamic rupture models.

Key Words
Rough faults, rate-and-state, cycle simulations

Citation
Heimisson, E. R. (2019, 08). Earthquake cycles on a self-similar rough fault: The importance of the minimum roughness wavelength. Poster Presentation at 2019 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)