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Gordon Bell Prize Winners Simulate Earth’s Mantle


Copyright: Vadim Sadovski
 

Some people still picture scientists dressed in lab coats, madly scribbling mathematical formulas on a chalkboard, or as swashbuckling Indiana Jones-types beating up on bad guys and cracking wise. But nothing could be further than the truth.

Such is the case for the winners of the Association for Computing Machinery’s prestigious Gordon Bell Prize in 2015. Their achievement: the most realistic simulation of the earth’s interior dynamics.

Thanks to their work, which included the development of advanced numerical algorithms to run on massively parallel systems—the IBM Sequoia BlueGene*/Q (BG/Q), located at the Lawrence Livermore National Laboratory in this case—and a rethinking of the end-to-end computational frameworks of such systems, they now have a better understanding of plate tectonics in relation to earthquakes and volcanic activity.

“Today, one of the interesting aspects of this work is demonstrating that these machines can be used efficiently for large, tightly coupled problems and that one can optimize codes to actually get good performance.”
—Georg Stadler, associate professor, Courant Institute of Mathematical Sciences, New York University

The team’s collaborative and discipline-diverse effort resulted in innovative algorithms that led the team’s code to reach a world-record 97 percent parallel efficiency in scaling the solver to 1.6 million cores. A few of the great minds behind this achievement are Michael Gurnis, director, Seismological Laboratory, California Institute of Technology; Georg Stadler, associate professor, Courant Institute of Mathematical Sciences, New York University; and Cristiano Malossi, research staff member, Foundations of Cognitive Solutions Group, IBM Research–Zurich.

IBM Systems Magazine (ISM): Why is the development of your simulation so important?
Michael Gurnis (MG):
A long-standing question is the science of what drives the plates. Why do the plates move on the earth’s surface, and why do the continents move around at the velocities they do? We generally understand the physics of this problem, but many unknowns remain unanswered. We don’t know exactly how the plates—such as the Pacific Plate that slides beneath Japan or the Nazca Plate, which is going beneath South America—and the forces pulling down on them bring them into the earth’s interior or how the energy is released.

Those are big problems because, ultimately, the ignorance of how this manifests itself results in a lack of understanding why we have great earthquakes and where they occur. What we’re trying to do is develop a framework in which we can put the physics we think are important into a computer model that’s connecting with different kinds of measurements we make near the earth’s surface.

The problem from the physics and computational perspectives is that in order to partly solve this problem, people have had to leave out an important part of the mechanics, which has two attributes. One is multiscale.

For example, the Pacific Plate is about 14,000 km across, from the eastern Pacific all the way to where it moves beneath Japan, but we don’t know the exact fault-length scale where one plate slips by another. It could be a kilometer in thickness, several meters or hundreds of meters. We don’t know.

It’s also both a solid problem and a fluid problem. So, the mechanical strength of the material varies by maybe 10 orders of magnitude over distances of tens of kilometers. No one had a numerical method that could solve this on a global scale. People have done what we call toy problems, where you do a little problem of just one particular plate boundary, but they’ve never scaled up to the whole earth. That’s what we’ve done here for the first time.

Jim Utsler, IBM Systems Magazine senior writer, has been covering the technology field for more than a decade. Jim can be reached at jjutsler@provide.net.



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