Stephen Grand, Professor Emeritus

After a stellar career in seismography, Professor Stephen Grand retired this fall. His scientific discoveries helped reveal new details about the inner workings of the Earth. At the same time, he was a dedicated member of the Jackson School of Geosciences faculty, supporting students and colleagues alike.

One of the most well-known images of the Earth’s interior depicts the subduction of the Farallon Plate, an ancient oceanic slab, beneath the North American Plate as it dips down into the lower reaches of Earth’s mantle. The image was produced by seismic tomography — a technology that uses seismic waves generated by earthquakes to reveal features of the Earth’s interior in a manner akin to a medical CT scan.

The plate’s journey to the deepest depths of the mantle came together into a discernible image thanks in part to the careful analysis and interpretation of Stephen Grand, a professor emeritus at the Jackson School of Geosciences.

The image — which appeared on the 1997 cover of GSA Today, the monthly magazine of the Geological Society of America — helped settle a big debate about whether subducted plates were confined to the upper part of the mantle or could circulate throughout the entire layer. It did so by showing two tomographical renderings, one created by Grand, the other by colleague Rob van der Hilst of the Massachusetts Institute of Technology. Together, the renderings presented clear evidence that the Farallon Plate was passing though most of the mantle, perhaps even making it to the mantle-core boundary.

“Our independently derived images looked similar, and that had a big effect on the geophysics community,” Grand said. “For the first time, slabs could clearly be seen descending into the deep mantle”

Grand has spent his career mapping the Earth’s interior by discerning different structures and processes using seismic tomography, drawing on seismic data from around the world. Most of Grand’s academic career has been spent in one place: the Department of Geological Sciences at The University of Texas at Austin (now the Department of Earth and Planetary Sciences). After 35 years at the department, Grand retired in August.

The American Geophysical Union recently recognized Grand’s contributions to the field of seismic tomography by presenting him with the 2022 Inge Lehmann Medal, which honors a senior scientist for outstanding contributions to the understanding of the structure, composition and dynamics of the Earth’s mantle and core. He is also an AGU fellow.

In addition to imaging the famous Farallon Plate, some of Grand’s other notable research accomplishments include improving the understanding of mantle convection, and working with his doctoral student, Peter Nelson, to reveal that the Yellowstone supervolcano is powered by a plume rising from the core-mantle boundary beneath Baja California. Later research proved that the tilt of the plume as it rises is due to mantle convection.

Grand’s research helped bring some of the most mysterious and inaccessible parts of the planet into view. Yet, looking back on his career, Grand admits that he had only a fuzzy idea of what he was doing when he decided to pursue a doctoral degree in geophysics in 1984. He enrolled as a graduate student at the California Institute of Technology because he had an undergraduate degree in physics from McGill University, a passion for mountains, and was interested in living on the West Coast.

An early research project introduced him to seismic tomography, and how seismogram “bumps” relate back to the inner workings of the planet.

“I found it really neat that as a student, I could actually look at waves that went deep in the Earth and say something new about the Earth’s interior,” said Grand. “After that, I got hooked on mapping out the interior of the Earth.”

Luckily for Grand, the field of seismic tomography was just getting started. There were many opportunities for exploration.

“Our knowledge of the inside of the Earth then was that there’s a crust, a mantle, a core — basically that was it. What we knew about the dynamics and composition of Earth was kind of an arm-waving cartoon,” Grand said. “I got into trying to map out what was actually down there using seismic waves.”

Grand’s seismic data sometimes came from pre-existing networks, but in many cases, he, along with postdocs and students, would set up their own stations for regional projects. This included networks in East China and Manchuria, Mexico, and a line of instruments stretching from West Texas to Utah.

According to Mark Cloos, a long-time colleague of Grand’s and a professor emeritus in the department, Grand’s range of insights about the inner Earth are a testament to his skill in data selection — from placing monitors, to deciding which earthquake events generated the most relevant seismic waves.

“Steve has the ability you need to zoom in on the details that are really important for the question at hand, so a lot of attention to detail,” Cloos said. “But he’s not a perfectionist. He gets things done, and he has certainly fostered that in his students to get them publishing on a fairly regular basis.”

In addition to his own research and the research of his students, Grand has played an integral role in supporting the department as an academic entity, Cloos said. Grand served as department chair from 2009 to 2011. And he spent years co-teaching with Leon Long (now a professor emeritus in the department) GEO 303, the introductory geology course for nonmajors. In this role, Grand opened the door to geology for many students.

“He is the perfect colleague and always has been” Cloos said of Grand. “He has always been here to make the place go.”

After a long career focused on the Earth’s interior, Grand said that he is looking forward to spending some time indulging in activities at the surface. That includes travel, spending time with his kids and, if all goes well, learning to cook and garden.