for a wide range of infrastructure,” said David McCallen, who leads an ECP-supported effort called High Performance, Multidisciplinary Simulations for Regional Scale Seismic Hazard and Risk Assessments. He’s also a guest scientist in Berkeley Lab’s Earth and Environmental Sciences Area. One of the most important variables that affect earthquake damage to buildings is seismic wave frequency, or the rate at which an earthquake wave repeats each second. Buildings and structures respond differently to certain frequencies. Large structures like skyscrapers, bridges, and highway overpasses are sensitive to low frequency shaking, whereas smaller structures like homes are more likely to be damaged by high- frequency shaking, which ranges from 2 to 10 hertz and above. Mc- Callen noted that simulations of high-frequency earthquakes are more computationally demanding and will require exascale computers. In preparation for exascale, McCallen is working with Hans Johansen, a researcher in Berkeley Lab’s Computational Research Division, and others to update the existing SW4 code — which simulates seismic wave propagation — to take advantage of the latest supercomputers, like the National Energy Research Scientific Computing Center’s (NERSC’s) Cori system. This manycore system contains 68 processor cores per chip, nearly 10,000 nodes, and new types of memory. NERSC is a DOE Office of Science national user facility operated by Berkeley Lab. The SW4 code was developed by a team of researchers at LLNL, led by Anders Petersson, who is also involved in the exascale effort. With recent updates to SW4, the collaboration successfully simulated a 6.5-magnitude earthquake on California’s Hayward Fault at 3 hertz on NERSC’s Cori supercomputer in about 12 hours with 2,048 Knights Landing nodes. This first-of-a-kind simulation also captured the impact of this ground movement on buildings within a 100-square-kilometer radius of the rupture, as well as 30 kilometers underground. With fu- ture exascale systems, the researchers hope to run the same model at 5-10 hertz resolution in approximately five hours or less. “Ultimately, we’d like to get to a much larger domain, higher frequency resolution, and speed up our simulation time,” McCallen said. “We know that the manner in which a fault ruptures is an important factor in determining how buildings react to the shaking, and because we don’t know how the Hayward fault will rupture or the precise geology of the Bay Area, we need to run many simulations to explore different scenarios. Speeding up our simulations on exascale systems will allow us to do that.” This work was published in a recent issue of Institute of Electrical and Electronics Engineers Computer Society’s Computers in Science and Engineering. Predicting earthquakes: Past, present, and future Historically, researchers have taken an empirical approach to estimat- ing ground motions and how the shaking stresses structures. So to pre- dict how an earthquake would affect infrastructure in the San Francisco region, researchers might look at a past event that was about the same size — it might even have happened somewhere else — and use those observations to predict ground motion in San Francisco. Then they’d
Researchers at Berkeley Lab, LLNL and UC Davis are utilizing ground motion estimates from a regional-scale geophysics model to drive infrastructure assessments. Image: courtesy of David McCallen
Simulated ground motions for an M 7.0 Hayward Fault earthquake showing (a) the magnitude of ground velocity at 10 s, (b) ShakeMap based on peak ground velocity for the 1D model, and (c) and (d) the same for the 3D model. Geologic features are Sacramento-San Joaquin Delta (Delta); East Bay Hills (EBH); Mount Diablo (MD); San Pablo Bay (SPB); and Dublin-Pleasanton- Livermore Tri-Valley (Tri-V). Image: courtesy of David McCallen
Utilizing ground motions to evaluate regional infrastructure risk with the Hayward Fault rupture scenario and resulting demands/risk on representative buildings (in terms of peak interstory drift). Image: courtesy of David McCallen
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