A tribute to Thomas C. Hanks, a USGS geophysicist who showed himself to be a generous mentor, as well as a leading scientist.
By Wayne Thatcher, U.S. Geological Survey
Tom was one-of-a-kind, and one of my oldest friends. We met as Caltech graduate students in the late 1960s. He stood out from the start: very self-confident, Princeton frat boy vibe, blowing smoke rings with his Lucky Strikes. Like that. His high intelligence was obvious, his intellectual curiosity insatiable. He needed to know how the Earth worked; he was going to find out and he was going to make his mark.
He and I bonded on a trip to England in 1968, where we attended a (not very good) international scientific meeting, after which we briefly visited Ireland and Wales. Tom had never traveled outside the country, whereas I’d done a gap year in Europe. I’d never cared much for beer, but Tom was a gifted beer drinker. I may’ve taught him a bit about international travel. He certainly taught me how to drink beer. And so, we became lifelong friends.
As a grad student, Tom had very original ideas and wide-ranging, eclectic interests. These included Earth’s thermal history, flexure of oceanic lithosphere at island arcs, thermo-mechanics of mid-oceanic ridges, as well as his main thesis work on seismic source mechanics. All resulted in well-received publications by the time Tom got his Ph.D. in 1972.
Collaborating with Tom as students, and later as professionals at the USGS, was quite a ride. We were both ambitious, competitive and hard-working — burning to succeed. And if I may say so now, we were perhaps a little too full of ourselves.
Our thesis advisor, Jim Brune, had written a brilliant theoretical paper on earthquake source characteristics with clear and immediate application to analysis of Caltech’s local earthquake seismogram collection. As a result, Tom and I worked furiously over several years to publish several influential and well-cited papers while still graduate students. We were definitely well launched, and definitely pleased with ourselves.
By the mid-1970s, Tom and my scientific interests followed separate tracks. Tom and his wife Peg started a family before my wife and me, and so our paths inevitably diverged. We nonetheless followed each other’s research, shared insights, and generally cheered on and supported one another. Tom continued to make important contributions to seismic source studies with particular application to estimating earthquake strong ground motion and its relevance to engineering seismology and probabilistic seismic hazard assessment (PSHA).
Concurrently, Tom, through his personal and professional friendship with USGS earthquake geologist Bob Wallace, became interested in the creation, preservation and erosion of the surface fault scarps created by earthquake faulting. This interest culminated in Tom’s intuitively appealing and mathematically straightforward model for the diffusional erosion of fault scarps and related landforms, like coastal marine terraces and those created by river erosion. It was an elegant, beautiful piece of science. Oh, how I wished I’d thought of it myself!
Tom’s later career included not only his continuing research interests, but also his service to the USGS and the earthquake science community. He served a term as chief of the Survey’s branch of ground motion and faulting. He led a 5-year-long project to estimate the upper bound of extreme ground motions that could be expected at Yucca Mountain, NV, then the proposed long-term nuclear waste storage repository for the United States. He also labored long to compose an accessible, plain-English primer on PSHA principles and practices that, although never formally published, was highly esteemed, widely read and very influential.
Tom was a generous and unselfish mentor to both young and not-so-young colleagues. He had a knack for gently engaging in ongoing scientific conversations that germinated ideas for productive new research. After helping to plant the seed, Tom would gracefully step back, allowing the colleague to carry the project to completion and shine in their own right.
I can speak to this approach from my own experience. Analyzing repeat Global Positioning System (GPS) observations from the Tibetan Plateau, I was able to make space-based geodetic estimates of present-day slip rates on the largest active faults in the region. Previous work, as well as my own, had uncovered large discrepancies between these rates and independently obtained geologic estimates. In discussing these disagreements with Tom, he quickly identified previously unappreciated problems with the geologic rates, telling me he’d write a ‘term paper’ for me on the topic. Several weeks later, my very own private copy arrived — an original, carefully reasoned critique describing serious shortcomings in the published geologic interpretations. As Tom pointed out, the methodology actually provided both upper and lower bound slip rates, with the lower bound being sensibly consistent with the geodetic rates. Tom’s ‘term paper’ was subsequently circulated around a small specialist community and soon informally accepted as a possible resolution to the slip rate discrepancy. Other geologists were independently reaching similar conclusions that subsequently appeared in several published papers. Their geologic interpretations, as well as Tom’s, are now generally accepted as definitive and the rate discrepancy is resolved. When I gratefully thanked Tom for setting me straight and offered co-authorship in my study he forthrightly declined, saying simply he’d done it “for friendship.”
In the last 15 or so years of his life, I saw another even more generous side of Tom. During that time, he increasingly cared for Peg, his wife of more than 40 years, as she declined from Parkinson’s disease. Determined that she should remain at home, he assumed the major role in her care until her death in 2020. As his own health subsequently declined, he nonetheless remained the same Tom, actively engaging with colleagues, enjoying the families of his two daughters — especially his two granddaughters — and closely following the fates of the San Francisco Giants. I had the good fortune to interact with him during his final year, going with him to the USGS offices periodically for meetups and seminars. Our conversations focused mostly on matters of the moment, but we also shared stories of our good old days — some of which may’ve even been true.
Tom was one of a kind, and one of my oldest friends. I, like many others will surely miss him.
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