George P. Woollard Award
Anthony B. (Tony) Watts
University of Oxford
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Presented to Anthony B. Watts
Citation by Marcia McNutt
The Woollard Award recognizes “outstanding contributions to geology through the application of the principals and techniques of geophysics.” Tony Watts is a most worthy recipient, having applied gravity, seismic, bathymetric, and stratigraphic data to the quantitative solution of problems in tectonics, geodynamics, geomorphology, and sedimentology. He has mentored dozens of post-docs and students, participated in more than 15 sea-going expeditions, and authored nearly 150 papers. His book, Isostasy and Flexure of the Lithosphere, is a tour de force, showing isostasy, modulated by the mechanical resistance to flexure, is the common cause shaping the structure of the crust in geological environments ranging from mid-ocean ridges to trenches, and from continental rifts to mountain belts.
Following in the footsteps of Woollard, Tony’s first major breakthrough came from constraining the deformation of the lithosphere beneath the load of the Hawaiian volcanoes using gravity data. Expressing the strength estimates in terms of the effective thickness of an elastic plate, he proposed the thickness increased as the square root of the age of the lithosphere at the time it was loaded by volcanism, and then remained frozen at that value as the load aged. Using this concept, he estimated ages of seamounts remotely from gravity anomalies, without recourse to geochemical analyses of rock samples. With his student Uri ten Brink, he was the first to observe directly the flexure of the lithosphere beneath the Hawaiian islands with multichannel seismic data and to image apparent ponding of magmatic material beneath the crust, termed “underplating”.
He then connected the long-term mechanical strength of the lithosphere to results from laboratory studies of rock defor-mation, building on an idea first suggested by Goetze and Evans. Tony and his students John Bodine and Mike Steckler combined rock mechanical studies showing brittle failure in the upper crust and creep at greater depths to define a ‘yield stress envelope’ that was temperature, and thus age, dependent. They successfully showed that mechanical loading of this rheologic structure would imitate the simple idealized elastic plate flexure.
Tony recognized the potential for flexural isostasy to explain a common pattern of coastal on-lap sequences observed in a variety of sedimentary basins in seismic reflection profiles. Other scientists had proposed that sea level rise was required to explain the global distribution of on-lap events. Tony’s work showed that this onlap sequence was a natural consequence of the increasing flexural rigidity of cooling, subsiding lithosphere, avoid the need for sea level changes. Tony expanded these ideas with his students Garry Karner, Mike Steckler and Julian Thorne and their Lamont colleague Bill Ryan, developing the ‘back-stripping’ technique to study the thermo-mechanical evolution of sedimentary basins. This led to a new understanding of the geologic forces that create source, reservoir, and trap rocks, and produce the thermal regime required to mature hydrocarbons. It even allowed a rough guess at the resource potential of a basin from its gravity anomaly alone, especially valuable when satellite altimetry furnished global marine gravity anomalies over previously unexplored areas.
Tony’s singular vision and greatest achievement has been to show the universality of isostasy and flexure of the lithosphere as common mechanisms shaping the architecture of the Earth’s crust across all geologic environments. Tony Watts, the intellectual heir to Woollard, is a particularly appropriate recipient of the 2005 Woollard Award.
2005 George P. Woollard Award - Anthony B. (Tony) Watts
Thank you Marcia for your kind words and the rest of the committee for nominating me for the George P. Woollard award.
It is a great honour to receive this award from the Geophysics Division of the Geological Society of America. I have very much enjoyed working at the boundaries of geophysics and geology, something which Martin Bott, my Ph.D thesis advisor, encouraged. I remember, as a young under-graduate, reading Martin’s papers that showed how you could use gravity anomalies to address the granite problem and thinking that this was exactly how geophysics should be used — as a tool to address geological problems.
Most of my working career has been spent in the US, which I think provides the most exciting environment to do research. My first opportunity was a post-doctoral fellowship at Columbia’s Lamont-Doherty Geological Observatory. When I arrived there in the early 70s Lamont was running 5 ships and in its heyday of ocean exploration. Doc Ewing sent me to work in the gravity group and I remember Manik Talwani asking me which ocean I wanted to work in. I answered the Atlantic because it was the only ocean that I knew anything about. My reward was to be sent to the Barents Sea with Captain Kohler on R/V Vema for 2 very cold (and dark) months! When I returned, Manik told me that he already had people working on the Atlantic and Indian oceans and that I should work in the Pacific. It was a decision I have never regretted. Lamont had amassed a huge geophysical database in the Pacific, which we were able to use to test the earlier ideas of Dick Walcott and Tom Hanks that the crust might be flexed seaward of trenches. The trench work led to Hawaii, two chance meetings with George Woollard, and a career long interest in plate flexure. Although I returned to the UK in the early 90s (where I finally got to work in the Atlantic!), I have able to maintain my US contacts, thanks to sabbaticals first at MIT and then at Scripps.
There are many people who I feel should share this award. First, are my graduate students whose friendship, advice, and never-ending enthusiasm has been an inspiration to me. Marcia has already mentioned some of them by name. I would like to add though a special thanks to Pål Wessel and Walter Smith who, in addition to completing very good theses, developed GMT which I, and many other scientists around the world, have greatly benefited from. Second, are my close working colleagues. Again, there are too many to mention. However, I would like to say a special thanks to Peter Buhl, Evgenii Burov, Jim Cochran, Christine Peirce, Jeff Weissel and Shijie Zhong. You have all helped to make this journey an enjoyable one and my passion for geology is as strong now as it was when I first started.