To make sure our buildings and infrastructure are earthquake-safe, we must understand how seismic activity affects different structures. Two major research efforts funded by the Department of Energy (DOE) seek to fill in the gaps and provide resources for researchers and engineers to study earthquakes across scales, from the initiation of seismic waves at the fault rupture site deep underground, to the interactions between shaking soil and individual structures at the surface.
The first endeavor is an experimental facility for real-world studies on how the soil around a structure influences its performance during an earthquake. During an earthquake, the movements of buildings are dictated by site-specific interactions between soil layers and the direction and strength of the vibrations. The Large-Scale Laminar Soil Box System will be the largest facility in the U.S. for studying these interactions.
Studies conducted with the Soil Box System will provide data for the other effort, EQSIM: an ongoing collaboration between scientists at Berkeley Lab, Lawrence Livermore National Laboratory, and the University to develop realistic, highly detailed earthquake simulations using DOE’s supercomputers.
The 15-foot-high, 21.5-foot-wide box sits on a 24-foot square shaking platform controlled by 16 hydraulic actuators. The soil container has 19 layers, called laminates, that are each supported on elastomeric bearings so that soil layers can move relative to each other like soil does during actual earthquakes. The system can displace and accelerate 350 tons of soil — and the structure on top — in two horizontal directions simultaneously with the same force as a strong earthquake. The hydraulics are controlled by custom software and the box is equipped with a suite of sensors so that the scientists can gather detailed datasets to feed into their computer simulations.
Current models of earthquake properties rely on approximations and simplifications due, in part, to the lack of real-world data on the fundamental physics involved, but also because very few computers on the planet can run earthquake simulations at the fidelity required to perform infrastructure damage assessments.
The research team has been using the Summit supercomputer at Oak Ridge National Laboratory and the Perlmutter supercomputer at Berkeley Lab to develop very large, detailed models — like their simulations of the San Francisco Bay Area for M7 Hayward fault earthquakes — which has 391 billion model grid points.
They will also soon start working on an even more capable platform, the newly launched Frontier supercomputer, also at Oak Ridge. Frontier is the first computer system to break the exascale barrier, meaning that it can calculate at least a billion billion (also known as a quintillion, or 1018) operations per second, and is currently ranked as the world’s most powerful supercomputer.
Using these exceptionally fast machines, the team will be able to add new insight and information on soil response and soil-structure interaction gained from the Soil Box experiments into their existing large-scale models.