Broadband Ground Motion Simulation Using a Hybrid Approach

Robert W. Graves, & Arben Pitarka

Under Review 2010, SCEC Contribution #1356

This paper describes refinements to the hybrid broadband ground motion simulation methodology of Graves and Pitarka (2004), which combines a deterministic approach at low frequencies (f < 1 Hz) with a semi-stochastic approach at high frequencies (f > 1 Hz). In our approach, fault rupture is represented kinematically and incorporates spatial heterogeneity in slip, rupture speed and rise time. The prescribed slip distribution is constrained to follow an inverse wavenumber-squared falloff and the average rupture speed is set at 80% of the local shear wave velocity, which is then adjusted such that the rupture propagates faster in regions of high slip, and slower in regions of low slip. We use a Kostrov-like slip-rate function having a rise time proportional to the square root of slip, with the average rise time across the entire fault constrained empirically. Recent observations from large surface rupturing earthquakes indicate a reduction of rupture propagation speed and lengthening of rise time in the near surface, which we model by applying a 70% reduction of the rupture speed and increasing the rise time by a factor of 2 in a zone extending from the surface to a depth of 5 km. We demonstrate the fidelity of the technique by modeling the strong motion recordings from the Imperial Valley, Loma Prieta, Landers, and Northridge earthquakes.

Citation
Graves, R. W., & Pitarka, A. (2010). Broadband Ground Motion Simulation Using a Hybrid Approach. Bulletin of the Seismological Society of America, (under review).