Paul Segall has contributed to observation, theory, and modeling of earthquake and volcanic processes inferred from surface geodetic measurements. Many practitioners in these fields, including past Whitten medalists, have had an impact on one of these specialist areas. His research on the earthquake deformation cycle has led to new kinematic and dynamical models and analysis methods that extract maximum information from space geodetic data and has shed new light on previously poorly understood earthquake processes. His work has quantified and constrained how volcanoes grow, evolve, and deform, and he has made state-of-the-art space geodetic measurements using models he has himself defined and developed from fundamental principles. Paul has made major contributions in all of them, his work defines where these fields are going, and Paul is their preeminent leader. Since 1990 he has trained a generation of graduate students and postdoctoral scholars, many of whom are now leaders in their fields in academia and government laboratories. His 2010 textbook Earthquake and Volcano Deformation, developed and refined over a decade of teaching, has become an instant classic, an essential reference for all researchers in this field.
Since the mid-1980s, Paul has led his field in modeling and understanding the earthquake cycle, its analysis, and state-of-the-art modeling of seismic processes. From the mid-1980s to the mid-2000s, he tested the prevailing models of earthquake recurrence. Paul and his coworkers developed creative and innovative methods entirely new to the field. These methods were strictly rigorous inversions and statistically defensible methods that showed the recurrence of earthquakes obeyed neither of the popular and prevailing models in use at the time (characteristic, time predictable and slip predictable).
Paul recognized early on significant methodological gaps in analysis of earthquake-related geodetic data. He developed ingenious new methods to extract maximum signal from sparse or incomplete data when the actual candidate models were at least approximately known (the now classic network inversion filter). The method is extremely flexible and versatile and is applicable to classical triangulation data to infer coseismic slip in historical earthquakes as well as to identify anomalies in GPS time series (for example, slow slip events or suspected earthquake precursors).
Paul and his students have developed geodetic methods to innovatively model the large-scale kinematics and dynamics of magmatic extension and intrusion, particularly on Hawaii. This work has shown not only that the south flank of the island is inexorably sliding toward the sea but also that it is driven by magma injection into the rift zones. Previously unknown silent slip events, associated with smaller triggered earthquakes and coupled to the injection events, have been identified.
—Wayne Thatcher, Earthquake Science Center, U.S. Geological Survey, Menlo Park, Calif
Thank you, Wayne, for the overly generous citation. Thanks also to those who took the time to support my nomination. It’s a particular honor for me to receive this award given the phenomenal group of prior medalists, including my former U.S. Geological Survey (USGS) colleagues Wayne Thatcher and Jim Savage. Charles Whitten himself was the chief geodesist of the U.S. Coast and Geodetic Survey, following in the footsteps of William Bowie and John Hayford. Hayford analyzed the triangulation data following the 1906 San Francisco earthquake, leading to H. F. Reid’s elastic rebound theory. Much later, I had the opportunity to reanalyze these same data, attempting to tease out more information about the 1906 quake, as well as the 1868 Hayward Fault earthquake.
I entered graduate school in 1976 at a time of great anticipation about earthquake prediction and was excited to work on problems with such potential for societal benefit. At Stanford, Arvid Johnson captured my interest and wisely directed me to work with Dave Pollard studying the formation of faults in granite. Following my Ph.D. work, I moved to USGS, where I was impressed with Jim Savage and Will Prescott’s crustal strain program. Following in Whitten’s footsteps, they were measuring strain accumulation on faults, but now with lasers. This struck me as providing unique information for long-term earthquake forecasting and tied in well with my interest in continuum mechanical models of earthquakes. They generously allowed me to work on data from the Parkfield area, beginning my exploration of tectonic geodesy.
Moving back to Stanford gave me the opportunity to work with an amazing group of students and postdocs. Thanks to all of you for helping me explore new Earth processes and learn new analysis methods. I continue to believe strongly that measurements of contemporary deformation, combined with physically consistent models, can contribute to reducing both earthquake and volcanic hazards. GPS and, later, interferometric synthetic aperture radar opened up new opportunities for data collection. What started as an attempt to write lecture notes of sufficient clarity that I could understand them 2 years later led to a textbook on active deformation processes. It’s a real pleasure when students tell me they have found it to be useful.
I’m so fortunate to have the opportunity to work with such outstanding colleagues. Coteaching with Greg Beroza has been both rewarding and informative. Jim Rice has been a generous collaborator and a role model of a scientist and teacher. Thanks, finally, to my friends, including my cycling buddies, and my family and most especially to my wife, Joan, for keeping me grounded.
—Paul Segal, Stanford University, Stanford, Calif.
Citation: AGU (2015), Paul Segall receives 2014 Charles A. Whitten Medal, Eos, 96, doi:10.1029/2015EO022051.