Adam Dziewonski was a giant in solid Earth geophysics, a major contributor to our knowledge of Earth’s internal structure, and a relentless advocate for the infrastructure needed to support research.
Adam was born in Lwów, then part of Poland, in 1936. While he was studying at the University of Warsaw, he participated in the Polish International Geophysical Year Scientific Expedition to Vietnam (1958–1959), where he was in charge of operating a remote geomagnetic observatory. The harsh conditions in the field gave him a keen appreciation for observatory science.
After earning a doctorate from the Academy of Mines and Metallurgy in Kraków (1965), Adam left for the Southwest Center for Advanced Studies in Dallas, Texas, where Anton Hales became his cherished mentor. In 1972, he moved to Harvard University and settled there for the rest of his career, retiring from teaching in 2009.
During his time in Dallas, Adam worked on mathematical techniques to quantify the dispersion of seismic surface waves. Notably, he developed the “multiple-filter technique” to extract single-mode group velocity dispersion by moving window analysis, an approach still used today.
With Freeman Gilbert, he collaborated on the measurement and analysis of normal mode eigenfrequencies from records of vibrations from the 1964 Alaska earthquake, obtaining the first direct proof that Earth’s inner core is solid (1971). Digitizing the Alaska data set took 2 years, something hard to conceive for young researchers entering the field today.
Global Earth Models and Preliminary Reference Earth Model
Combining the 1964 normal mode data set with other available data provided unprecedented constraints for the development of several one-dimensional global Earth models. Then, in 1977, the International Union of Geodesy and Geophysics asked Adam and Don L. Anderson to construct a reference Earth model for the benefit of the community.
The resulting Preliminary Reference Earth Model (PREM, 1981), which, for the first time, included radial anisotropy and depth-dependent attenuation, met with resounding success. It was called “preliminary” because, as Adam said in his 2015 tribute to Don Anderson, “we thought that it would be improved in a few years.” At present, PREM is still a reference model of choice in seismology and is widely used by the mineral physics community to test candidate mantle and core compositions.
A Pioneer in Global Seismic Tomography
In 1976–1977, Adam spent a year at the Lincoln Laboratory at the Massachusetts Institute of Technology, where he could access and analyze the unique global travel time data set assembled by the International Seismological Centre, then freshly available on magnetic tapes. Using 700,000 P travel time residuals (differences between the observed and predicted travel times of seismic P waves), he obtained the first global long-wavelength three-dimensional (3-D) model of Earth’s lower mantle (1977).
With then graduate student Brad Hager and Hager’s adviser Rick O’Connell, Adam discovered the negative correlation between degrees 2 and 3 structure seismic structure in the deep mantle and the geoid. The robustness of this striking deep structure was later confirmed in a higher-resolution study (1984), highlighting, for the first time, the presence, near the core-mantle boundary, of a ring of high velocities surrounding two large antipodal and equatorial low-velocity regions. These features, now awkwardly named “large low-shear-velocity provinces”—Adam recently preferred the term “pillars of the Earth”—are still the focus of many deep-Earth studies.
The arrival at Harvard of John Woodhouse in 1979 started a decade of fruitful collaborations, producing some major achievements. These include the following:
- development of the centroid moment tensor (Harvard CMT) methodology using long-period waveforms to infer earthquake source parameters (1981)
- development of the first global 3-D upper mantle model entirely based on long-period teleseismic waveforms (1984)
- discovery, with graduate student Andrea Morelli, of inner core anisotropy (1986) to interpret the travel times of inner core–sensitive P waves
Adam, a tenacious workaholic, and John would work late at night because “things were most quiet then.” Adam chain-smoked during these late-night sessions, until he suddenly decided to quit on 16 January 1987, a date he still remembered 30 years later. Still further discoveries were in store, notably, with graduate student Miaki Ishii in 2002, the identification of a region of distinct anisotropy in the central part of the inner core, which they called the innermost inner core.
Over the next decades, as he and his students developed several generations of global mantle shear velocity models, Adam always insisted on the significance of “degrees 2 and 3 structure”—the longest wavelength heterogeneity in the mantle—for mantle dynamics.
Adam, Ved Lekic, and I recently continued investigating this topic. Until shortly before his death, Adam had been advising us on the construction of a 3-D reference Earth model, a critical step beyond PREM for further advances in the understanding of mantle mineralogy and dynamics. We will miss his insight and wisdom as this project develops!
An Advocate for Broadband Seismology Infrastructure
When broadband digital seismology became a reality in the mid-1970s, Adam embraced the quest for developing a new generation of state-of-the-art global seismic observatories. With a handful of midcareer seismologists from academia, with whom he shared enthusiasm, vision, and energy, he worked relentlessly on the establishment of the Incorporated Research Institutions for Seismology (IRIS). When IRIS was finally established in 1984, he served on its first executive committee and later chaired several others.
Adam contributed in other ways toward the seismological infrastructure of today. With graduate student Joe Steim, he initiated and supported the development of the Very-Broadband Seismometer (1986), which became the gold standard for the International Global Seismographic Network. He was a founding member of what’s now the International Federation of Digital Seismograph Networks (FDSN, 1986), which still coordinates instrument standards and data exchange internationally. He was also a founding member of the International Ocean Network (ION, 1992), which aimed to extend the deployment of broadband seismic observatories to the ocean floor. He advised the International Seismological Centre and served as chair of its governing council from 1998 to 2005.
Adam was a man of relatively few words, which he chose carefully. He defended his vision with a strong and deep voice that made a lasting impact. Most recently, he proposed the Global Array of Broadband Arrays (widely known as GABBA) as the next ambitious endeavor for global seismology, a concept that is making its way in the community.
Adam’s influence reached well beyond global seismology. He was keenly aware of the importance of combining different disciplines to really understand “how the Earth works.” In this context, he was a key player in the development of the now thriving Cooperative Institute for Dynamic Earth Research (CIDER).
Adam shared the 1998 Crafoord Prize with Don L. Anderson “for their fundamental contributions to our knowledge of the structures and processes in the interior of the Earth.” He received the 2002 Bowie Medal from the American Geophysical Union (AGU) and many other honors, including the Gold Medal of the Ettore Majorana Foundation and Centre for Scientific Culture (1999) and the Harry Fielding Reid Medal of the Seismological Society of America (1999). He was elected to the National Academy of Sciences in 1995.
Adam greatly inspired several generations of young researchers and unselfishly supported the careers of those in whom he recognized talent. I had the privilege of closely collaborating with him on many infrastructure endeavors since the mid-1980s, notably FDSN, ION, and, most recently, CIDER, and I enjoyed many stimulating research discussions with him, even as we often sparred. I will miss him as a mentor, collaborator, and close friend.
—Barbara Romanowicz, Department of Earth and Planetary Science, University of California, Berkeley; e-mail: [email protected]