By Lina Sorg
High-performance computing (HPC), coupled with vast amounts of digital data and immersive three-dimensional (3D) visualization techniques, is steering computational fluid dynamics in a new direction. HPC’s prevalence in most modern computing applications demands cutting-edge tools to adequately visualize the resulting data. In some cases, such as with 3D virtual reality (VR), these tools literally take users inside data. 3DVR adds a new dimension of physical meaning to numerical models by allowing users to study 3D conceptualizations of Earth’s modern subduction systems as if they were tangible concepts.
During a minisymposium presentation at the 2019 SIAM Conference on Computational Science and Engineering, currently taking place in Spokane, Wash., Margarete Jadamec of the State University of New York at Buffalo applied HPC and 3DVR to the geophysics problem of plate tectonics. Scientists cannot directly access Earth’s interior, which comprises a laterally-variable geometry with discontinuous features and flow fields governed by nonlinear viscosity. Analysis of the interior requires dynamically emergent localized flow predictions, high-resolution methods to resolve features, and algorithms to solve for nonlinear flow. “3DVR is critical when data or a model is 3D and the results are not known a priori,” Jadamec said. “It’s hard to imagine something you really don’t know.” She drew a relatable parallel to children trying to visualize the contents of a refrigerator. If you present them with two-dimensional (2D) slices through a fridge that contain a Tupperware of spaghetti, they have to extrapolate that the slices of Tupperware actually represent a 3D object.
Both GPS data and geological constrains confirm that Earth’s lithosphere (the outermost layer, consisting of the crust and upper mantle) is continuously moving. 15 major plates—ranging from 0 to 250 kilometers in thickness and characterized by convergent, divergent, or shearing motions—make up the oceanic and continental lithosphere. At points where plates converge and the denser oceanic layer sinks (becoming the subducted lithosphere), researchers use seismic images, seismic velocities, and plate locations to identify where the subductive material is at depth. While researchers traditionally utilized 2D models to display seismic data, complicated flow patterns, pressure gradients, and variations in subduction zones have rendered these models inadequate. “We can conceptually abstract that there are variations in the lithosphere, but extrapolating whole-scale plates descending into the interior is a challenge requiring three dimensions,” Jadamec said.
She employs a VR user-interface toolkit called the ShowEarthModel program to map data onto Earth and examine the resulting modern slab morphologies, including the presence of slab-edge volcanoes. The program yields 16 visualizations of “tours” through Earth’s interior that preserve scientific content and extrapolate information from 2D cross-sections into three dimensions. These visualizations can take place in a virtual reality room, though movies that zoom into Earth (and consequently into the data) achieve the same depth perception. Jadamec’s videos reveal discontinuity in the subductive lithosphere and variability in the inclination of the downgoing plate within just one subduction zone. “HPC can incorporate this complexity, whereas 10 to 20 years ago we didn’t have the facilities to model this kind of phenomena,” she said.
Jadamec then spoke about the benefits of analyzing one’s data in an immersive 3DVR setting called the Cave Automatic Visual Environment (CAVE). CAVE allows users to map subduction zones onto a grid, witness the resulting thermal structure, and observe the downgoing plate’s variable geometry and upper plate’s lateral variations in thickness. She solves Stokes equations for incompressible flow and Stokes equations with nonlinear viscosity; these significantly impact runtimes, allow scientists to scale up to a larger problem, and model the distribution of viscosity variations at shear zones. Such investigation reveals that the descent of Earth’s outer layer into the mantle weakens the surrounding area and affects the velocity magnitude. “You have this halo of perturbed mantle affected by the downwell, the subduction of that plate,” Jadamec said.
In conclusion, Jadamec demonstrated how advanced computational resources—namely HPC and 3DVR—propel a novel path in geodynamics research. Her 3D visual simulations accurately capture the variety of movements in subduction and modern plate morphologies in a way that 2D models cannot. 3D models allow researchers to interact with and identify different flow types around slab edges and localized upwellings that explain slab-edge volcanoes and other tectonic manifestations on Earth’s surface. “The interactivity is a critical component of this work,” Jadamec said. “It makes for a very efficient realization of real-time hypotheses from which you can target various analyses."