USGS, Menlo Park, Calif.
Wayne Thatcher received the Whitten Medal at the 2004 Fall Meeting Honors Ceremony on 15 December, in San Francisco, California. The medal is given for outstanding achievement in research on the form and dynamics of the Earth and planets.
Citation
Armed with geodesy, Wayne Thatcher has probed the behavior of great earthquakes, concentrating on the two sites where large events are frequent and the geodetic record is lush: the western United States and Japan. From this, he has garnered deep insights into the earthquake cycle—the pattern of strain accumulation and release of which an earthquake is only the most visible part.
Building on the work of H. F. Reid, who in 1910 gave us the elastic rebound theory of earthquake occurrence, Thatcher was the first to use geodetic measurements to analyze variations in strain throughout the earthquake cycle. Using data from repeated triangulation surveys, he mapped the strain released in the 1906 San Francisco earthquake and the subsequent strain accumulation. Remarkably, these data had been little studied since Charles Whitten established many of the networks in the 1930s to 1950s. Combining these measurements with elastic dislocation theory, Thatcher found that the 1906 earthquake was surprisingly shallow—470 km long but just 10 km deep.
Thatcher first identified accelerated strain following the 1906 earthquake, which he ascribed to slow slip beneath the rupture. He further demonstrated that the maximum shear-strain rate decayed exponentially since 1906, and that the strain concentration at the fault broadened with time. Decades after initial publication, we continue to rely on these papers to address questions raised by the 1906 earthquake, its influence on events like the 1989 Loma Prieta shock and other Bay Area earthquakes, as well as present-day seismic hazards in the San Francisco Bay area.
Wayne’s collaborative work on the earthquake cycle in Japanese subduction zones has shaped our thinking about megathrusts. Thatcher was the first to show evidence for short-term transient deformation near subduction zones, which he suggested was due to after-slip; and longer-term transients, which he argued were caused by viscoelastic relaxation of the asthenosphere underlying the elastic crust. Differentiating between what Wayne coined as the “thin lithosphere” and “thick lithosphere” models of postseismic deformation continues to be a first-order objective of research. Recent research by Thatcher and his colleagues on postseismic measurements suggests that the crust is stronger than the ductile uppermost mantle where relaxation is focused.
Wayne was quick to embrace space-based geodetic methods and their promise of enhanced precision and density. His GPS transect across the Basin and Range province for the first time provided direct measurements of the distribution of strain within the region, showing that strain is concentrated in just a few active belts near the edges of the Great Basin. He has also established a strong USGS program using satellite radar interferometry (InSAR) to image deformation around magmatic systems and active faults in the western United States, working with USGS colleagues to uncover unexpected mobility of magmatic systems and to place better constraints on postseismic processes.
In a sense, Wayne’s most recent work largely answers the thin-versus-thick lithosphere conundrum he posed at the outset of his career: The higher-quality data now available suggest that a mobile upper mantle plays a very significant role in driving observed postseismic deformation. At the same time, an attribute that has marked Wayne’s career from its inception and has never wavered is that he resists the temptation to overstate his findings, never presents his views as incontrovertible, remains open to new ideas, and is always excited by what’s coming next.
—ROSS STEIN, USGS, Menlo Park, Calif.
Response
I thank you, Ross, for your generous citation, and I’m honored to receive this recognition from AGU. It is most gratifying to me that colleagues and friends like Ross and Paul Segall saw fit to nominate and support me—no one ever receives such an award without these essential, selfless actions. Of course I am pleased to receive it, too, but for me the scientific life has always been its own reward. I’ve always felt lucky to have colleagues who are both supportive and demanding, and I’ve been fortunate to spend most of my working life at the U.S. Geological Survey, where good science is encouraged and respected. It should go without saying that any individual award owes more than a little to valued colleagues and a tolerant institutional environment.
The plate tectonic revolution occurred while I was a grad student, and like many of us in solid Earth science my subsequent research has often been focused on mining its consequences and implications. In my specialty, tectonic geodesy, two broad topics have guided my work: (1) the earthquake deformation cycle at major plate boundaries; and (2) continental deformation and plate tectonics. Soon after finishing my Ph.D., I was distracted from seismological research by an underexploited century-long record of classical geodetic measurements—triangulation and leveling—that provided important constraints on the deformation cycle at strike-slip plate boundaries in California and subduction boundaries in Japan. The inventions of space geodesy during the past 15 years led me to the second topic, because GPS methods are the perfect tool for quantifying the deformation of the continents and are now finally beginning to address issues that have remained unresolved since the late 1960s. GPS and InSAR methods are also providing spectacular refinements in our knowledge of the earthquake cycle and many surprises about the restless behavior of magmatic systems.
As mentioned above, I’ve been fortunate with my colleagues and coworkers. Though the list is inevitably incomplete, I wish especially to thank my thesis advisor, Jim Brune; my colleagues Jim Savage, Tom Hanks, John Rundle, Ross Stein, Paul Segall, David Hill, Philip England, and Fred Pollitz; and the marvelous group of postdocs who have worked with me over the past decade: Takeshi Sagiya, Chuck Wicks, Gerald Bawden, Takuya Nishimura, Bill Hammond, and Marleen Nyst. They’ve all taught me a lot, made science fun, and, when necessary, taken me in hand and held me to a high standard. In the matter of standards, I’ve tried to hew to the principles described by English Nobel laureate Peter Medawar in his Advice to a Young Scientist (1979). In particular, he said, “It is no kindness to a colleague—indeed it might be the act of an enemy—to assure a scientist that his work is clear and convincing…” [if one’s opinion is otherwise]. So I’ve always encouraged those whose judgment I respect to be completely candid in sharing their views on my work. They have been—how shall I put it?—extremely enthusiastic, in honoring this earnest request. However ego deflating and even painful this may have been at times, such open criticism has been immeasurably important in my career.
Indeed, one may argue that it is essential to the success of the scientific method. Finally, I want to especially thank my wife, Mary Ellen, and son, Iain, who have not only put up with me and endured the time-intensive rigors of my scientific life, but also encouraged and supported me in this strange passion.
—WAYNE THATCHER, USGS, Menlo Park, Calif.