Remembering Don L. Anderson

Don L. Anderson, the Eleanor and John R. McMillan Professor of Geophysics, Emeritus, passed away on December 2, 2014. He was 81 years old.

Anderson's work helped advance our understanding of the composition, structure, and dynamics of the earth and of earth-like planets. He was a pioneer in the use of seismic anisotropy—variations in the velocities of seismic waves as they move at different angles through materials—to study the earth's interior. This allowed him and others to learn more about the boundaries of the planet's mantle.

"Caltech has lost a towering figure in geophysics with the passing of Don Anderson," says Michael Gurnis, the John E. and Hazel S. Smits Professor of Geophysics. "Don left an indelible mark not just on the Seismological Laboratory but on the field of global seismology and whole-earth geophysics. He was an unusual scientist who often advocated unpopular theories and concepts. Perhaps more than anyone else, DLA—as he was fondly known in the Seismo Lab—knew how uncertain many of our observations and theories were, especially those of the earth's deep interior. By advocating the unpopular, Don challenged our ideas and forced us to make the observations needed to resolve our understanding of earthquakes and the deep earth."

In 1981, Anderson developed, with Adam Dziewonski of Harvard University, the Preliminary Reference Earth Model (PREM), a one-dimensional model representing the average properties of the earth, including seismic velocities, attenuation, and density, as a function of planetary radius. PREM continues to be the most widely used standard model of the earth. Anderson, a former president (1988–1990) of the American Geophysical Union, is the author of the book, Theory of the Earth, a 1989 reference on the origin, composition, and evolution of Earth's interior. In 2007, Anderson published New Theory of the Earth, a completely updated version.

Born in Frederick, Maryland, on March 5, 1933, the son of a schoolteacher and an electrician, Anderson received his BS in geology and geophysics from Rensselaer Polytechnic University in 1955. He worked for Chevron Oil Company from 1955 to 1956, the Air Force Cambridge Research Center from 1956 to 1958, and the Arctic Institute of North America from 1958 to 1960.

His service with the Air Force took him to Greenland, where his job was to determine how thick the ice had to be to support aircraft that were in trouble. "The Air Force wanted their pilots to land disabled planes on the sea ice, but the conventional wisdom at the time was that they would break through the ice and the crew would freeze to death," Anderson recalled in a 2001 oral history. Anderson and his colleagues found that, in fact, aircraft can land very easily on ice that is not very thick: "Even if the ice won't support the plane while it's sitting there, it will allow a plane to taxi long enough for the pilots to get out and then the plane can sink through the ice, or the wheels can poke through the ice. Our job was to study ice strength, and whether you could determine how strong it was before you landed so you would know where to land." The project continued after Anderson entered graduate school at Caltech, where he earned a master's degree in geophysics in 1959 and a doctorate in geophysics in 1962 under the supervision of Frank Press.

Upon his graduation from Caltech, Anderson was hired as a research fellow; he became an assistant professor in 1963, an associate professor in 1964, and a professor in 1968. From 1967 to 1989, Anderson was director of Caltech's Seismological Laboratory.

"Those who were fortunate enough to be at the Seismo Lab with Don since the 1960s have greatly benefited from the interaction with him, and his influence will have long-lasting effects on our work for years to come," says Hiroo Kanamori, the John E. and Hazel S. Smits Professor of Geophysics, Emeritus. "As many of the Seismo Lab alumni would testify, we all benefited tremendously from the Seismo Lab coffee break discussions where Don was always at the center. Occasionally, he forcefully presented his idea, but more often he was a good listener too. Then, we later received notes and reprints on the subjects discussed, and if we were really interested in the subject, we would pursue it in depth and eventually write an interesting paper. Many of my papers grew out of the coffee break discussions."

"Don was a inspiring geoscientist who motivated his students and many younger colleagues to think deeply, broadly, and creatively about the Earth and other planets," says Thomas Jordan (PhD '72), a former student of Anderson's who is now the William M. Keck Foundation Chair in Geological Sciences and professor of Earth sciences at the University of Southern California.

Provost Edward Stolper, the William E. Leonhard Professor of Geology and the Carl and Shirley Larson Provostial Chair, agreed, saying "Don had a significant impact on my career—both as a supportive, probing, and intellectually challenging colleague, and as a friend.

"As a graduate student at Harvard, I heard Don lecture about the possibility of there being a CAI-like zone around the earth's core and about the composition of the moon. CAI's are calcium-aluminum inclusions in chondritic meteorites and represent the very earliest solid materials formed in the solar system. I was energized by what Don had said and knew at that point I wanted to be at Caltech," says Stolper.

Anderson was the Eleanor and John R. McMillan Professor from 1989 until his retirement in 2002.

"Don had a tremendous influence on the development of geophysics and global seismology in the United States," says Gurnis, the current director of Caltech's Seismological Laboratory. "One of DLA's unwavering passions since the 1960s was to map the earth's deep interior associated with surface processes. He was instrumental in founding the NSF-funded IRIS—Incorporated Research Institutions for Seismology—and the development of what became known as the GSN—the Global Seismic Network—in the 1980s. Through these major U.S. programs, we were able to map out the nature of the forces associated with plate tectonics and volcanism."

Anderson continued to work and publish until his death. His most recent work on volcanism was showcased at the fall meeting of the American Geophysical Union in San Francisco in December 2014.

A fellow of the American Academy of Arts and Sciences and a member of the National Academy of Sciences and the American Philosophical Society, Anderson was also the recipient of the Emil Wiechert Medal of the German Geophysical Society, the Arthur L. Day Medal of the Geological Society of America, the Gold Medal of the Royal Astronomical Society, the William Bowie Medal of the American Geophysical Union, and the Crafoord Prize of the Royal Swedish Academy of Sciences.

In 1998, Anderson was awarded the National Medal of Science and was cited for his "immeasurable influence on the advancement of earth sciences over the past three decades nationally and internationally."

Anderson is survived by his wife, Nancy; daughter, Lynn Rodriguez; son, Lee Anderson; and four granddaughters.