Victoria University of Wellington, New Zealand
Richard I. Walcott received the Charles A. Whitten Medal at the 2001 Fall Meeting Honors Ceremony on 12 December in San Francisco, California. The medal recognizes outstanding achievements in research on the form and dynamics of the Earth and planets.
Citation
“In the 19th century, geodesy—the measurement of the shape of the Earth—became the first part of the Earth sciences where rapid progress became possible through accurate measurement. The group who first exploited this technique on a large scale was the Indian Survey, based at Dehra Dun. Its measurements in India led to the idea of isostasy, but the group’s influence was much greater: the people it trained went all over the world making accurate geodetic measurements and thinking about the results. For a long period the survey’s research dominated the development of geodynamics and is now slowly doing so again. One of the people who has brought about this recent change is Dick Walcott, and it is partly for this reason that he is the recipient of the 1999 Charles A. Whitten Medal.
“Dick’s early research for his Ph.D. concerned the geology of the Red Hill complex in New Zealand, an ophiolite complex cut by the Alpine Fault. The origin and emplacement of such complexes have long puzzled petrologists, and his work was carried out shortly after the association of such structures with oceanic crust had been recognized. However, field studies of ophiolites are notoriously difficult, and Dick left this field when he moved to British Columbia, Canada, as a postdoctorate in 1966. A year later, he moved to the Dominion Observatory in Ottawa, where he stayed for 8 years until he returned to New Zealand in 1975.
“I first met Dick at this time, when I visited the observatory. He was working on one of the classical geophysical problems of interest since the 19th century: lithospheric flexure. Dick had realized that this subject was central to understanding how plates could move. What particularly interested him was the gravity signature of flexure, and he used this to estimate the elastic thicknesses of continental and oceanic plates. His early estimates of flexural rigidity, made in the space domain, have been confirmed by studies using the much larger data sets now available and spectral techniques in the frequency domain as well as space domain modeling. These studies have confirmed the accuracy of Dick’s early estimates, which showed how thin the elastic layer is that is responsible for the rigid motion of the plates.
“In 1975 Dick returned to New Zealand and again changed the direction of his research, this time to one that every geodesist would recognize as geodesy! The plate boundary between the Australian and Pacific plates crosses New Zealand, and the relative motion of these plates is responsible for the seismic activity and quaternary deformation that is such a striking feature of the country. When Dick returned, he started a major project to understand how this deformation was related to the motion of the plates on either side. There are a number of reasons why New Zealand is a good place to carry out such a study. It is one of the relatively few places where continental tectonics occurs between plates whose velocity is known from oceanic spreading rates. In addition, 19th century geodesists, trained in India by the survey, had surveyed the islands with extraordinary care and accuracy. But perhaps the most important reason is that there was a small group of outstanding Earth scientists and geodesists in the Wellington area of New Zealand, all of whom Dick knew well. So he did not have the problem faced by most geologists and geophysicists in other parts of the world who wished to use geodetic measurements for tectonic purposes—namely, convincing the geodesists that the movements are real and not the result of surveying errors. What Dick and his colleagues found was that the deformation was distributed over a wide region as it crossed New Zealand and also that it involved rotations as well as translations. In a beautiful use of yet another field of geophysics, he then used paleomagnetic measurements to demonstrate the existence of these rotations. He is now exploiting the new space-based geodetic techniques, and especially the Global Positioning System, to examine the deformation in more detail.
“Dick’s research involves geodesy in its widest sense. He is one of a very small band of people who has brought the subject back to its rightful place at the center of geophysics. It is fitting that his great contribution to our understanding of tectonics should be honored by the Charles A. Whitten Medal.”
—DAN P. MCKENZIE, University of Cambridge, England
Response
“The award of the Charles A. Whitten Medal has a particular pleasure for me, as I enjoyed meeting Charles at several AGU meetings. He took a serious interest in the research activities of the time, particularly those involving survey data with which he was familiar, and he was invariably helpful and supportive. I thank the AGU for the award and this opportunity to acknowledge debts to several people.
“Earlier this year, Harold Wellman died in Wellington. He was the most eminent geologist of this century in New Zealand and, by far, the dominating personality in the Geology Department at Victoria University where I studied. He was noted for a number of major contributions; the stratigraphy of the New Zealand Cretaceous and the discovery of the Alpine fault as a major continental strike-slip fault are examples. But to my mind, his most important characteristic was his quantitative approach to geological deformation, which probably came about through his earlier training as a surveyor. To Harold, description was not explanation—an uncommon geological view of the time—and my interest in the measurement of Earth deformation by whatever means was something acquired from him. In 1967 I obtained my first job with the Gravity Division of Energy Mines Resources Canada in its systematic gravity mapping of the country, and an inevitable problem of interpretation of gravity was the nature of the compensation for topographic loads. It was the very different behavior of the Earth in northern Alberta compared to the Basin and Range Province that focused attention on the problem of flexure. Surfaces underlying the flat-topped Caribou Mountains in Alberta showed no deflection because of their very substantial load, yet if the Earth behaved the same way as Crittenden had described for Pleistocene Lake Bonneville, we would expect to see a downward flexure of several kilometers. Because this was not so, the lithosphere had to support the load and spread the compensation and thus be many times stiffer under the Interior Plains of Canada. From that conclusion it was natural to proceed to estimating the stiffness of the lithosphere in other examples of surface loading.
“I returned to New Zealand in 1975 and joined Hugh Bibby in extending his earlier work on measurement of shear strains from reobservations of old surveying networks. Repeated triangulation estimates of deformation resulting from earthquakes were common in New Zealand and elsewhere, but with the instruments then available, only changes in angles could be determined with accuracy so that the displacement vector of any particular trig point could not be obtained. However, as F.C. Frank showed, the shear-strain components of the deformation of any triangle could be unambiguously measured. Hugh had showed that repeated triangulations could indeed give sensible shear-strain estimates in an area of rapid tectonic deformation and, importantly, that the triangulations need not be of highest geodetic standard; old surveys, although not of great accuracy in themselves, could provide excellent estimates of the deformation because of the long period between repeated surveys. It was clear that abundant information already existed in national archives to obtain extensive coverage and thus map the rate and direction of relative displacements during the intervening period. With mapped shear strains it was possible to estimate the kinematics of the deformation. Thus it was shown that the current rate of deformation across the Pacific-Australian plate boundary through New Zealand had the same sense, rate, and direction as that predicted by the Euler vector describing relative plate motion on a geological timescale.”
—RICHARD I. WALCOTT, Victoria University of Wellington, New Zealand