Bryan Isacks

Bryan L. Isacks was an American geophysicist whose seismology helped turn plate tectonics from a contested idea into the organizing theory of modern Earth science. Born in New Orleans on 25 July 1936, he was raised by his mother, Sue Bryan Isacks, after his father, Leonard Smith Isacks, died in the Second World War. He studied at Columbia University on scholarship and began his career there as a geophysicist, building field camps from the Arctic to the Andes and the South Pacific.

In 1968, with Jack Oliver and Lynn Sykes, he published "Seismology and the New Global Tectonics," which used earthquake patterns and focal mechanisms to show that intermediate and deep earthquakes occur within sinking slabs of oceanic lithosphere. That work, and related papers with Muawia Barazangi and others, made subduction and plate motion visible in seismic data and remains a landmark of the plate-tectonic revolution. In 1971 Isacks moved with Columbia colleagues to Cornell University, where he became the William and Katherine Snee Professor of Geological Sciences, directed the Institute for the Study of the Continents, and chaired geological sciences from 1994 to 2003.

At Cornell he helped lead the Andes Project, mapping steep and flat segments of the Nazca plate beneath South America and linking Andean topography to lithospheric processes. He was an early adopter of digital elevation models, coined ideas such as the glacial "buzz saw," and later used satellite remote sensing as a NASA Earth Observing System investigator of climate in high mountain systems. Locally he studied how ice sheets sculpted the Finger Lakes and advocated for Ithaca's Museum of the Earth, where a model glacier exhibit illustrates that landscape history.

Colleagues described him as an unassuming genius and a generous mentor. In 2014 the American Geophysical Union awarded him the Walter H. Bucher Medal, citing that "no one has made a greater contribution to our understanding of the subduction of oceanic lithosphere." After a severe stroke in 2020 he remained connected to family, students and colleagues. He died in Ithaca on 9 September 2026, aged 90, from complications of that stroke. He is survived by his wife, Marjorie Olds; children Lillian, Katherine, Susan, Bryan Jr., Brett Olds and Robert Olds; and grandchildren.