This NSF award to Princeton University funds U.S. researchers participating in a project competitively selected by the G8 Research Councils Initiative on Multilateral Research through the Interdisciplinary Program on Application Software towards Exascale Computing for Global Scale Issues. This is a pilot collaboration among the U.S. National Science Foundation, the Canadian National Sciences and Engineering Research Council (NSERC), the French Agence Nationale de la Recherche (ANR), the German Deutsche Forschungsgemeinschaft (DFG), the Japan Society for the Promotion of Science (JSPS), the Russian Foundation for Basic Research (RFBR),and the United Kingdom Research Councils (RC-UK), supporting collaborative research projects selected on a competitive basis that are comprised of researchers from at least three of the partner countries.
The primary goal of this international project involving collaborating researchers in three countries is the development of sophisticated 3D seismic imaging tools for the characterization of earthquakes, Earth 'noise', and mapping of Earth's interior on all scales. The research affects the fields of exploration geophysics, regional and global seismology, and even helioseismology. The proposed research ensures that seismologists will be able to effectively and efficiently harness future high performance computers. The project will develop and enhance open-source software for the simulation of 3D seismic wave propagation in acoustic, (an)elastic and poroelastic media on hierarchical computer architectures. These simulations account for heterogeneity in the crust and mantle, topography, anisotropy, attenuation, fluid-solid interactions, self-gravitation, rotation, and the oceans. A major goal is to be able to routinely and efficiently reach a shortest period of 1 s in global simulations, the shortest period signal that propagates across our planet.
This NSF award supports the education and training of a postdoc. Software developed during the course of the proposed research period will be made freely available via the Computational Infrastructure for Geodynamics (CIG). The award also supports the further development and enhancement of the southern California and global ShakeMovie web sites.
Over the proposed research period we developed and enhanced open-source software for the simulation of 3D seismic wave propagation on parallel computer architectures, i.e., to address the forward problem in seismology. These simulations account for heterogeneity in the crust and mantle, topography, attenuation, fluid-solid interactions, gravitation, rotation, and the oceans. As a result of our efforts, we are now able to routinely and efficiently reach a highest frequency of 1 Hertz in global simulations, the highest frequency signals that propagate clear across our planet. In the context of the seismological inverse problem, we harnessed the power of the forward modeling tools to enhance the quality of images of Earth's interior and the earthquake rupture process. The approach minimizes differences between simulated and observed seismograms based on 'adjoint' techniques in combination with 'conjugate gradient' methods, an iterative approach we refer to as ‘adjoint tomography’. Over the course of the research period, we performed adjoint tomography of Europe and Asia. The resulting images of the crust and mantle address unresolved tectonic and geodynamical questions for these regions. Additionally, we have initiated adjoint tomography of the entire planet, which is a perfect example of the 'development of application software towards exascale computing for global issues' mentioned in the G8 Research Councils Initiative on Multilateral Research Funding call for proposals. We plan to publish our first global model by the end of 2015. With regards to education and outreach, all software developed during the research period is open source and freely available via the Computational Infrastructure for Geodynamics. The resources helped to further develop the global ShakeMovie system, which analyzes all global earthquakes of magnitude 5.5 and greater. For the general public, this analysis includes production of an animation showing the evolution of the seismic wavefield generated by the earthquake as a function of time.
