Brittany A. Erickson, Zheqiang Shi, and Steven M. Day

Department of Geological Sciences

San Diego State University


The Dependence of High-Frequency Characteristics of Ground Motion on Rupture Model Parameters

Research Objectives:

Recent 3-D numerical simulations reveal that high-frequency ground motion generated from rupture propagation on rough faults is influenced by the properties of fault roughness, frictional parameters, and off-fault plastic response. In particular, the predicted Fourier spectra of ground acceleration from rupture along faults with self-similar roughness are roughly flat between a few tenths of a Hz and a source-controlled upper cutoff frequency. Fourier spectra of recorded ground motion exhibit a similar upper cutoff frequency, conventionally called f_max, which appears to be principally controlled by path and site attenuation. An open question is the extent to which the path and site effects overprint a source-controlled contribution to f_max such as that found in the numerical simulations. As a step toward addressing that question, we refine the theoretical predictions by further examining the sensitivity of source f_max to rupture model parameters. Initial findings from our earlier 3-D simulations (Shi and Day, 2013) have identified three key sensitivities: a downward shift of source f_max occurs when (i) the off-fault material undergoes plastic deformation (relative to the corresponding elastic simulations); (ii) the minimum roughness wavelength of the fault profile is increased; and/or (iii) the state evolution distance in the friction law is increased. These effects are both nonlinear and strongly coupled to each other. In this work, we perform a more extensive parametric study with 2-D rough-fault simulations to examine the aforementioned f_max sensitivity factors, their scaling with event magnitude and roughness amplitude, and their dependence on the plastic yielding parameters.

2013 AGU Annual Meeting