3-D Seismic Wave Propagation on a Global and Regional Scale: Earthquakes, Fault Zones, Volcanoes

For computational seismology the present years are extremely exciting. The reason is, that with the current supercomputer technology, the frequency band in which seismic waves are observed following regional or global earthquakes, can be simulated numerically for realistic 3D earth models for the first time. Depending on the spatial scales under consideration (whole planet, a sedimentary basin at risk from local earthquakes, a volcano with high risk for future eruptions) this will lead to considerable improvement (1) in the understanding of the structural properties (e.g. the Earth’s mantle, the inside of a sedimentary basin or a volcano) and (2) in forecasting strong ground motion for realistic earthquake scenarios. The latter point may have considerable long-term societal benefits, as the short-term prediction of large earthquakes seems out of sight. During the first phase of this project some of the highest-resolution simulations ever done were carried out with important implications for future directions in computational seismology. The most important scientific results can be summarized as: (1) 3D Simulations of several earthquakes in the Cologne Basin in Germany demonstrate that the main characteristics of ground motion (e.g. peak motion amplitude, shaking duration) are successfully predicted through numerical simulations; (2) The low seismic velocities inside active faults (e.g. San Andreas Fault, California) may act as an amplifier for ground motion. This has implications for buildings in the vicinity of faults; (3) Large scale simulations of strong earthquakes in subduction zones show that the local 3D structure at depth strongly influences the waves propagating to the surface. Ignoring this will lead to severe misinterpretations. (4) Including topography to understand wave propagation inside volcanoes is crucial. Our simulations demonstrate the scattering effects due to topography. If we want to understand the state of a volcanic system prior to eruptions from seismic waves these effects have to be taken into account.