Current methods in global or local-scale seismic tomography rely on approximate
descriptions of wave propagation
with the result of severely limiting the resolution of
tomographic images. However, to truly understand the dynamics of our planet, we need to
be able to seismically map its deep structure at resolutions much higher than it is nowadays
possible. Major geophysical questions that require high resolution 3D imaging at the
planetary scale include a better understanding, e.g., of the nature of mantle plumes and
sinking tectonic plates. At the regional scale, reliable seismic images are crucial for
more accurate earthquake location and the compilation of seismic hazard maps.
Recent advances in algorithms, software development, and high performance computing
systems have resulted in PDE-based solvers that scale up to millions of variables,
make use of thousands of processors, and accommodate complex multiple-physics. As partial
differential equations (PDE) solvers also mature in the Earth Sciences, there is an
increasing interest in solving nonlinear seismic inversion problems governed by PDE-based
models. Larger computer architectures and new algorithms for optimization and wave
propagation now provide the computational ability to address the geophysical issues
mentioned above in a more rigorous way: namely, to abandon asymptotic ray-theory
approximations in favor of time-dependent PDE-based models, and replace linearized
inversions by truly nonlinear optimization. To achieve this goal, it will be necessary to
combine recent developments in computational methods for nonlinear optimization and wave
propagation, such as high-order finite element discretizations, local time-stepping,
iterative methods, and inexact parallel interior-point methods.
More specifically, the scientific goals of the project are: to develop parallel numerical methods for forward wave propagation and large-scale
nonlinear optimization, to explore the performance of such methods on emerging petascale architectures (e.g.
GPU, Cell BE) and to develop a new generation of a seismic inversion code for 3D Earth imaging.