High-resolution Dynamic Rupture Simulations Using Local Time Stepping

Realistic fault rupture simulations often require local refinements in numerical meshes to accurately capture e.g. complex fault geometry and fault roughness. Together with explicit time schemes, this dramatically reduces the global time step size for ground motion simulations due to numerical stability conditions. To alleviate this problem, local time stepping (LTS) algorithms allow an explicit time stepping scheme to adapt the time step to the element size, allowing near-optimal time steps everywhere in the mesh. This can potentially lead to significantly faster simulation runtimes. Combining our new multi-level LTS-Newmark scheme with spectral-element method (SEM) dynamic rupture simulations, we highlight the high-performance computing implementation of our scheme into the open-source SPECFEM3D_Cartesian package. Our new LTS scheme inherently extends the 2nd-order accurate Newmark time-stepping scheme, and leads to an efficient parallel implementation, producing realistic scenario speedups of multi-resolution seismic applications. Together with advances in exploiting hardware accelerators such as graphic processing units (GPUs) for deterministic ground motion simulations, we demonstrate performance speedup using a state-of-the-art dynamic earthquake rupture model for the Tohoku-Oki event.