Next-Generation Local Time Stepping for the ADER-DG Finite Element Method
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High-frequency ground motion simulations pose a grand challenge in computational seismology. Two main factors drive this challenge. First, to account for higher frequencies, we have to extend our numerical models, e.g., by considering anelasticity, or by including mountain topography. Second, even if we were able to keep our models unchanged, simply doubling the frequency content of a seismic wave propagation solver requires a sixteen-fold increase in computational resources due to the used four-dimensional space-time domains. This work presents the Extreme Scale Discontinuous Galerkin Environment (EDGE) in the context of high-frequency ground motion simulations. Our presented enhancements cover the entire spectrum of the unstructured finite element solver. This includes the incorporation of anelasticity, the introduction of a next-generation clustered local time stepping scheme, and the introduction of a completely revised communication scheme. We close the modeling and simulation loop by presenting our new and rich preprocessing, which drives the high problem-awareness and numerical efficiency of the core solver. In summary, the presented work allows us to conduct large scale high-frequency ground motion simulations efficiently, routinely and conveniently. The soundness of our work is underlined by a set of high-frequency verification runs using a realistic setting. We conclude the presentation by studying EDGE's combined algorithmic and computational efficiency in a demanding setup of the 2014 Mw 5.1 La Habra earthquake. Our results are compelling and show an improved time-to-solution by over 10x while scaling strongly from 256 to 1,536 nodes of the Frontera supercomputer with a parallel efficiency of over 95
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