Geoscientists at The University of Texas at Dallas recently used massive amounts of earthquake data and supercomputers to generate high-resolution, 3D images of the dynamic geological processes taking place far below the Earth's surface.
In a study published April 29 in Nature Communications, the UT Dallas research team described how it created images of mantle flows in a subduction region under Central America and the Caribbean Sea using a computationally intensive technique called a full waveform inversion (FWI).
University of Texas at Dallas geoscientists used earthquake data and a computationally intensive technique called a full waveform inversion to create 3D images of the geometry of subducting slabs (green bodies) and induced mantle flows (yellow arrows) under Central America and the Caribbean Sea at a depth of 500 kilometers.
Credit: University of Texas at Dallas
"This is the first comprehensive seismic study to directly image 3D mantle flow fields in actual subduction environments using advanced FWI technology," said Dr. Hejun Zhu, corresponding author of the study and assistant professor of geosciences in the School of Natural Sciences and Mathematics.
Dr. Jidong Yang, who earned his PhD in geosciences from UT Dallas in May, and Dr. Robert Stern, professor of geosciences, are the study's co-authors.
A Dynamic Earth
Between the relatively thin layer of the Earth's crust and its inner core lies the thickest part of the planet, the mantle. Over short time periods, the mantle can be considered solid rock, but on the geological time scale of millions of years, the mantle flows like a viscous fluid.
Earth's crust is broken into pieces called tectonic plates. These plates move across and into the mantle very slowly -- about as fast as fingernails grow. At regions called subduction zones, one plate descends under another into the mantle.
"The sinking of oceanic plates into the Earth's mantle at subduction zones is what causes the Earth's tectonic plates to move and is one of the most important processes taking place in our planet," Zhu said.
"Subduction zones are also the source of many natural hazards, such as earthquakes, volcanoes and tsunamis. But the pattern of mantle flow and deformation around descending plates is still poorly understood. The information our techniques yield is crucial for understanding our dynamic planet."
Zhu and his colleagues tackled the problem using a geophysical measurement called seismic anisotropy, which measures the difference in how fast mechanical waves generated by earthquakes travel in different directions inside the Earth. Seismic anisotropy can reveal how the mantle moves around the subducting plate. Similar technology is also used by the energy industry to locate oil and gas resources.
"When a diver dives into water, the water separates, and that separation in turn affects the way the water moves around the swimmer," Zhu said. "It's similar with oceanic plates: When they dive into hot mantle, that action induces mantle separation and flow around the plates."
The research team created the images using high-fidelity data recorded over a 10-year period from 180 earthquakes by some 4,500 seismic stations located in a grid across the U.S. The numerical calculations for the FWI algorithm were performed on the high-performance computing clusters at the National Science Foundation (NSF)-supported Texas Advanced Computing Center at UT Austin, as well as on supercomputers at UT Dallas.
"Previously we couldn't 'see' under the Earth's surface, but by using this technology and this very wonderful data set, we are able to delineate the 3D distribution of various seismic phenomena and tell at what depths they are occurring," Zhu said.
Gone to Pieces
The images confirmed that the plates in the study region are not large, solid pieces but rather are fragmented into smaller slabs.
"This looks different from the textbook depictions of tectonic plates coming together, with one solid piece of oceanic plate descending under another solid piece," Zhu said. "Some researchers have hypothesized that this fragmentation occurs, and our imaging and modeling provides evidence that supports that view."
Zhu's 3D model shows complex mantle flow patterns around a number of descending fragments and in the gaps between slabs. Such chunky, fragmented pieces are seen in regions throughout the world, Zhu said.
In the northwestern U.S., for example, the Juan de Fuca Plate is also fragmented into two pieces where it descends under the North American Plate in the Cascadia subduction zone, an area where strong earthquakes have occurred over the centuries.
"We know that most earthquakes happen at the interface between a slab and the mantle. If there is a gap between these fragments, what's called a window region, you wouldn't expect earthquakes there," Zhu said. "If you look at the earthquake distribution along the Cascadia subduction zone, there is a span where you do not have earthquakes. That is probably a region where there is a gap in the subducting oceanic plate.
"The Middle America Trench that we studied has its own unique, dynamic properties. In the future, we plan to shift our attention to other subduction zones, including the Kermadec-Tonga subduction zone in the region of the Australian and Pacific plates."
The research was funded by a grant to Zhu from the NSF's Division of Earth Sciences.
Amanda Siegfried | EurekAlert!
NASA analyzes Tropical Cyclone Cristina's water vapor concentration
09.07.2020 | NASA/Goddard Space Flight Center
In the Arctic, spring snowmelt triggers fresh CO2 production
06.07.2020 | San Diego State University
New insight into the spin behavior in an exotic state of matter puts us closer to next-generation spintronic devices
Aside from the deep understanding of the natural world that quantum physics theory offers, scientists worldwide are working tirelessly to bring forth a...
Kiel physics team observed extremely fast electronic changes in real time in a special material class
In physics, they are currently the subject of intensive research; in electronics, they could enable completely new functions. So-called topological materials...
Solar cells based on perovskite compounds could soon make electricity generation from sunlight even more efficient and cheaper. The laboratory efficiency of these perovskite solar cells already exceeds that of the well-known silicon solar cells. An international team led by Stefan Weber from the Max Planck Institute for Polymer Research (MPI-P) in Mainz has found microscopic structures in perovskite crystals that can guide the charge transport in the solar cell. Clever alignment of these "electron highways" could make perovskite solar cells even more powerful.
Solar cells convert sunlight into electricity. During this process, the electrons of the material inside the cell absorb the energy of the light....
Empa researchers have succeeded in applying aerogels to microelectronics: Aerogels based on cellulose nanofibers can effectively shield electromagnetic radiation over a wide frequency range – and they are unrivalled in terms of weight.
Electric motors and electronic devices generate electromagnetic fields that sometimes have to be shielded in order not to affect neighboring electronic...
A promising operating mode for the plasma of a future power plant has been developed at the ASDEX Upgrade fusion device at Max Planck Institute for Plasma...
07.07.2020 | Event News
02.07.2020 | Event News
19.05.2020 | Event News
10.07.2020 | Life Sciences
10.07.2020 | Materials Sciences
10.07.2020 | Life Sciences