Generating 10 Hz deterministic broadband ground motions using kinematic source descriptions

William H. Savran, Kim B. Olsen, & Steven M. Day

Published August 15, 2017, SCEC Contribution #7732, 2017 SCEC Annual Meeting Poster #250

Small buildings, such as single and multi-family residences, are most susceptible to seismic waves between 5 and 10 Hz. Therefore, it is crucial we understand the behavior of these high-frequency waves to provide informed seismic hazard assessments. Broadband physics-based ground motion simulations provide insight into ground motions from future earthquakes; however, calculating the high-frequency wave-field poses significant challenges. In addition to understanding the small-scale properties of the earth’s crust and upper mantle, characterizing the high-frequency behavior (>1 Hz) of the earthquake’s source remains a largely unsolved problem. One promising approach to broadband ground motion simulations uses a dynamic rupture calculation on a geometrically rough fault. While this approach has been shown to capture a number of key features of recorded ground motion, its modeling advantages come at a high computational cost. Here, we present a new kinematic source model based on the statistics of rough-fault dynamic rupture simulations.

For our kinematic source model, we build a 4D random variable consisting of slip, Δu, peak-slip velocity, vpeak, rupture velocity, vrup, and initial friction, μ0. Fault roughness introduces variations in μ0 and influences the rupture process causing spatial correlations between these parameters. To capture these correlations, we define a linear model of coregionalization using nested exponential variogram functions with range parameters of 250m and 7500m. We use sequential Gaussian simulation to create stochastic fields representing these source parameters after conditioning the model with a given distribution of μ0. To describe the rupture process in time, we use a regularized Yoffe function, thereby introducing three additional parameters: rise time, τr, peak time, τs, and initial rupture time, t0. Using relationships derived from experimental and numerical results we calculate distributions of τs and τr. Next, we calculate t0 by defining a hypocenter and converting vrup to t0 using a fast-marching eikonal solver. We show that our rupture generator produces fully-deterministic ground motions comparable with leading GMPEs up to 10 Hz, and produces flat far-field acceleration spectra. With further validation, this source model can be used to infer realistic broadband ground motions for future earthquake scenarios, as well as a means to generate realistic source descriptions on the SCEC Broadband Platform.

Key Words
High-F, Broadband Ground Motion Simulations, Kinematic Rupture Generator, Geometrically Rough Faults

Citation
Savran, W. H., Olsen, K. B., & Day, S. M. (2017, 08). Generating 10 Hz deterministic broadband ground motions using kinematic source descriptions. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Ground Motions