Many would agree that the recognition of plate tectonics has been the most significant development in the geosciences since Darwin and Wallace proposed evolution by natural selection. Reduced to its essence, plate tectonics includes seafloor spreading, transform faulting, subduction of oceanic lithosphere, and rigid-body motion of lithospheric plates. No one has made a greater contribution to our understanding of the subduction of oceanic lithosphere than Bryan Isacks.
With Jack Oliver, Isacks reintroduced the concept of the lithosphere and showed how its subduction explained a plethora of peculiarities of island arc structures. Isacks, Oliver, and Lynn Sykes wrote definitive papers showing how many key aspects of plate tectonics are defined by earthquake seismology. In these papers Bryan demonstrated that fault plane solutions of intermediate and deep-focus earthquakes require that those earthquakes occur within the downgoing slab of lithosphere, and he used those solutions to place constraints on the forces that drive plate motion. With Muawia Barazangi and others, he showed that the deep structure of back-arc basins implied seafloor spreading there.
Like most major contributors to plate tectonics, Bryan moved away from it in the 1970s, and he turned to subduction beneath a continental margin, the Andes, where the idealized rules of plate tectonics fail. With Barazangi and in a later elaboration with Teresa Jordan and others, he pointed out the geologic similarity between portions of the Andes where subduction occurs at a gentle angle and what geologists had inferred for the tectonic development of the western United States from 80 to 50 million years ago. His leadership in this area of research made Cornell a major center of Andean research.
Then 25 years ago, Isacks was one of the first to exploit digital topography to understand both geodynamics and erosion. He combined the fact that glaciers form at high altitudes with the widely accepted notion that glaciers erode more rapidly than rivers, and he coined the term “glacial buzz saw” to explain the hypsometry with seemingly flat high terrain despite many deep glacial valleys.
An unusually humble man, Isacks has received only one important accolade, the respect and appreciation of many students; ~35 of the ~45 graduate students whom he had advised attended a celebration of his 70th birthday. Until now, Bryan Isacks may have been AGU’s most outstanding scientist who had never received a medal or formal recognition of his contributions. We are delighted that this oversight has now been set right.
—Peter Molnar, University of Colorado Boulder, Boulder, Colo.
—Frank Richter, University of Chicago, Chicago, Ill.
Earthquake hypocenters recorded in the Andean Southern Puna seismic array (25–28°S, 70–65°W) provide new constraints on the s...
We investigate the depths of crustal earthquakes (<80 km depth) of the central Andes (5°S to 35°S) to constrain the relati...