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College Geophysicist Honored

Renowned scientist Tom Jordan receives medal

By Eva Emerson
February 2005

The American Geophysical Union has named USC University Professor Thomas Jordan the winner of the 2005 Inge Lehmann Medal.

Jordan, holder of the W.M. Keck Chair in Geological Sciences and a professor of earth sciences in USC College, received the medal in recognition of his outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth's mantle and core.

“Tom Jordan has proved himself a leader in his field many times over. We are thrilled to hear that his peers have once again chosen to recognize him for the excellence of his scholarship,” says Joseph Aoun, dean of USC College.

“This is a great honor for me,” says Jordan, the director of the Southern California Earthquake Center. “Inge Lehmann was a real seismological hero, and I've spent a significant part of my scientific career following in her footsteps.” As an example of how he has been inspired by Lehmann’s work, Jordan says that in the 1990s he and his students were able to explain an enigmatic feature in the Earth's upper mantle discovered by Lehmann a half century earlier.

Jordan is an internationally known geophysicist. His interest in the composition, dynamics and evolution of the solid Earth has fueled decades of research on seismology, plate tectonics, the formation of continents, mantle structure, sea floor morphology, earthquakes and active fault systems. SCEC, centered in USC College, is the nation’s largest university-based, multi-institutional center for the study of earthquakes and the hazards they pose.

In awarding Jordan the medal, the AGU mentioned a series of Jordan’s major discoveries about the three-dimensional structure of the Earth, many of which can be traced to his development of a number of key seismological techniques. These techniques helped to better elucidate structural features of the Earth's interior and remain in wide use today. In the 1970s, Jordan showed that the ancient parts of the continents have deep, chemically distinct "keels" that move with the continents during plate tectonic motions. He also discovered that the convective flow that drives plate tectonics extends much deeper into the Earth's mantle than had been previously thought, which set the stage for dynamical models of mantle convection.

He is an elected member of the National Academy of Sciences, the American Academy of Arts and Sciences, and the American Philosophical Society.

Jordan has received numerous accolades for his work, and has been a fellow of the AGU since 1983. He received the MacElwane Medal of the American Geophysical Union in 1983, the Woollard Award of the Geological Society of America in 1998, and the National Associate Award of the National Academy of Sciences in 2001. He is the author or co-author of some 150 scientific publications, including the recent report of the National Academy of Sciences, Living on an Active Earth: Perspectives on Earthquake Science, and the popular textbook, Understanding Earth (4th edition).

The Lehmann Medal is given every other year during the annual meeting of the AGU. Jordan will be formally presented with the award in December 2005.

Inge Lehmann was a Danish seismologist whose painstaking examination of seismograph records and ability to discard unessential detail led to her discovery of the Earth's inner core, one of the most important advances in our knowledge of the Earth's interior. Previously, the core was assumed to be homogeneous, but Lehmann's work showed that the behavior of seismic waves and their time curves could be explained more satisfactorily if a distinct central part were reflecting the compressional waves. Lehmann later went on to become an authority in the structure of the upper mantle of the Earth.

Inge Lehmann is the only woman to have been awarded the Bowie Medal, the highest award given by the AGU. In honor of that achievement and her many contributions to research on the Earth's mantle and inner core, the AGU established a medal in her name. The first Lehmann Medal was awarded in 1997.