FESD Type I: Earthquake Fault System Dynamics

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Great earthquakes occur at the boundaries of the world's tectonic plates where an increasing fraction of the population is exposed to high seismic risk. This project develops and uses large-scale computer simulations to investigate fault system interactions that control the occurrence and characteristics of earthquakes occurring along plate boundary fault systems. The project will develop computer models of the North American plate boundary, which consists of the subduction zone of Southern British Columbia, Washington, Oregon, and Northern California; and the San Andreas fault system of Northern and Southern California. This research addresses the short-term (minutes to years) predictibilty of earthquakes, and long-term processes (100-1000 years) that condition fault systems to fail in great earthquakes. To better characterize the magnitude and variability of ground shaking in damaging earthquakes, which is needed for increasing our resilience to earthquake disasters, the fault system models will be integrated with advanced ground motion simulations.The highly concentrated deformation of the brittle crust at plate boundaries largely occurs through the integrated slip of faults in geometrically complex fractal-like fault systems. Fault slip phenomena, including earthquakes, continuous fault creep, slow slip events, earthquake afterslip, and earthquake repeaters, with their exceptionally wide range of temporal and spatial scales, are products of the rich array of interactions that operate in these systems. The simulations of plate boundary fault systems developed by this project will span 10,000yrs of plate motion and consist of up to106 discrete events. Simulations on this scale are now possible due to advances in our understanding of fault constitutive properties and the interactions that give rise to the different modes of fault slip; growth of knowledge to define the 3D geometry of plate boundary fault systems; and development of numerical methods that permit highly efficient simulations across a very wide range of spatial and temporal scales. System-level simulations provide an experimental capability to probe these very complex systems to better understand the interactions that give rise to observable effects, and to advance predictive capabilities. In addition, simulations provide the means to integrate a wide range of observations from seismology, tectonic geodesy, and earthquake geology into a common framework. Probabilistic seismic hazard analysis (PSHA), the main tool used by earthquake scientists and engineers to ensure seismic safety in the built environment, requires long-term forecasting of ground motions of all potentially damaging earthquakes. This research will integrate the fault system models with advanced fault rupture and ground motion simulations to investigate the statistical nature of strong ground motions needed for reliable PSHA.