Broadband (0-4 Hz) Ground Motions for a Magnitude 7.0 Hayward Fault Earthquake With Three-Dimensional Structure and Topography

We performed fully deterministic broadband (0-4 Hz) high-performance computing ground motion simulations of a magnitude 7.0 scenario earthquake on the Hayward Fault (HF) in the San Francisco Bay Area of Northern California. Simulations consider average one-dimensional (1-D) and three-dimensional (3-D) anelastic structure with flat and topographic free surfaces. Ground motion intensity measures (GMIMs) for the 3-D model display dramatic differences across the HF due to geologic heterogeneity, with low wave speeds east of the HF amplifying motions. The median GMIMs agree well with Ground Motion Prediction Equations (GMPEs); however, the 3-D model generates more scatter than the 1-D model. Ratios of 3-D/1-D GMIMs from the same source allow isolation of path and site effects for the 3-D model. These ratios show remarkably similar trends as site-specific factors for the GMPE predictions, suggesting that wave propagation effects in our 3-D simulations are on average consistent with empirical data. Plain Language Summary With the use of powerful supercomputers and an efficient numerical method, modeling of ground shaking for a magnitude 7.0 earthquake on the Hayward Fault results in more realistic motions than previously achieved. The model includes the current best representation of the Earth (geology and surface topography) to compute seismic wave ground shaking throughout the region. Shaking intensity shows differences across the Hayward Fault that arise from rocks of different geologic origin. On average, results are consistent with models based on actual recorded earthquake motions from around the world. This study shows that powerful supercomputing can be used to calculate earthquake shaking with more realism than previously obtained.