UCSB Broadband Simulation Method of Broadband Ground Motion for Kinematic Earthquake Sources

Abstract:

We report modifications of UCSB broadband simulation method (Liu et al., 2006; Schmedes et al., 2013; Crempien and Archuleta, 2016), which models the synthetic broadband strong ground motions using a deterministic approach. The realization of fault rupture is represented kinematically and incorporates spatial heterogeneity in slip, rupture speed, rise time and peak time. Transformed to wavenumber the prescribed slip distribution has a k^-2 decay for high wavenumbers. The rupture front is a tortuous, multiply connected (“lacy”) fractal polyline that occupies a strip of finite width close to slip-pulse width (Gusev, 2014) but has no correlation with fault slip (Schmedes et al., 2009). A modified Yoffe function, which is defined by peak time and rise time, is used to approximate the local slip rate. In wavenumber the prescribed spatial distributions of rise time and peak time also follow inverse wavenumber fall-offs, but with fall-off rates of 1.75 and 1.0, respectively (Schmedes et al., 2013). Rise time and fault slip also have a correlation of 0.75. Each mean value scales with earthquake magnitude (Somerville et al., 1999). Finally, the moment-rate spectrum of this kinematic model is constrained to approximate the double-corner frequency spectrum JA19_2S (Ji and Archuleta, 2020). We demonstrate the fidelity of the technique by modeling the strong-motion recordings from three large earthquakes of the 2019 Ridgecrest sequence.