The primary goal of this project is to use seismic data to image Earth structure and seismic sources based on modern numerical methods and imaging techniques. We will further develop and enhance software for the simulation of 3D seismic wave propagation, with a particular emphasis on computing on Graphics Processing Units, rather than traditional Central Processing Units, potentially providing an order of magnitude increase in simulation speed. The broader impacts of the proposal include open-source software packages for the simulation of seismic wave propagation. Simulations based on these packages may be used to investigate seismic hazard and aid in the determination of tomographic images of Earth's interior and earthquake source parameters. All software developed during the course of the proposed research period will be made freely available via the Computational Infrastructure for Geodynamics (geodynamics.org).
The simulations of seismic wave propagation account for heterogeneity in Earth's crust and mantle, topography& bathymetry, seismic anisotropy, attenuation, fluid-solid interactions, self-gravitation, rotation, and the oceans. The main intellectual merit of this project revolves around harnessing the power of the forward modeling tools to enhance the quality of images of Earth's interior and the earthquake rupture process. The approach is to minimize remaining between simulated and observed seismograms based on so-called adjoint techniques in combination with conjugate gradient methods, an approach we refer to as "adjoint tomography". Specifically, following a successful application in southern California, we will 1) develop open-source GPU-based forward and adjoint spectral-element solvers, 2) perform adjoint tomography of Europe, 3) further develop noise cross-correlation tomography based on adjoint methods, 4) move towards adjoint tomography of the entire planet, and 5) extend the southern California and global "ShakeMovie" cyber infrastructure.