# Albert Tarantola

**Albert Tarantola** was a Spanish-born physicist (Barcelona, June 15, 1949 — December 6, 2009), of the University of Paris (Institut de Physique du Globe), and author of the book *probabilistic formulation of inverse problems* (Tarantola, 1987, 2005). Tarantola was the leader of the Geophysical Tomography Group, that during the years 1985—2000 developed modern methods for the interpretation of waveform data. Apart from doing scientific research, Tarantola has taught both at his own institute in Paris and at other universities.

## SEG Maurice Ewing Medal 2018

Albert Tarantola is universally recognized as the principal contributor to the emerging field of full-waveform inversion. His writings on the subject have become legendary. He was also the first to recognize the close relationship between seismic migration and seismic inversion by proving that seismic migration is the first step in an iterative attempt to solve a full-waveform seismic inversion problem. His pioneering research in inverse problem theory, Bayesian probabilistic formulation, and uncertainty analyses has had a far-reaching impact not just in exploration geophysics, but also in global geophysics, medical imaging, and other branches of science and economics.

### Biography Citation for the 2018 Maurice Ewing Medal ^{[1]}

Albert Tarantola was one of the foremost theoretical geophysicists of his generation. He was a genius, full of energy and enthusiasm, which are rare traits among great theoreticians. His traits were extreme in every sense of the word, in his life as well as in his way of thinking. Albert left Spain at an early age for Paris, where he built a successful career. His first doctorate degree was in astrophysics. He became interested in the early development of global navigation satellite systems, subsequently in global positioning systems and geodesy. He used the relativity theory to apply corrections between different satellites and clocks, got interested in geophysics, and completed a second doctorate degree in geophysics.

Working with Bernard Valette at the Institut de Physique du Globe de Paris, he wrote two of the most important papers on inverse theory titled “Inverse problems: Quest for information” and “Generalised non-linear inverse problems solved using the least squares criterion.” They were written in 1982 using a probabilistic approach, setting up the framework for discrete inverse problems. The papers were instantaneously recognized by the earth science community.

Albert extended this theory to seismic waveform inversion and wrote several papers, starting from acoustic to elastic. These papers formed the foundation of seismic full-waveform inversion. He established the concept of adjoint source and the crosscorrelation between modeled data and residual in order to compute the gradient for waveform inversion.

He also showed that the first iteration of seismic waveform inversion is migration. The industry recognized the importance of this work and funded a consortium where he started testing these ideas on synthetic and real data and where he trained brilliant students who took positions in the industry.

I joined the group in 1988. Coming from the analytical school, I had to fight my way in as Albert did not believe in approximations or working in transformed domains, such as frequency domain. Albert was a purist and believed in numerical methods. Recognizing the importance of computers in seismic waveform inversion, Albert established a national super-computing center at IPG Paris.

Identifying the limits of conversional waveform inversion, Albert moved his attention to important sampling using Monte-Carlo methods. He then published several papers with Klaus Mosegaard and established a whole new area of research. In his view, we should sample the whole model space and look at movies and images that most often appear to be the most probable solution, providing a posteriori probability distribution. In the later part of his life, he started working on the law of physics using his probabilistic approach and wrote a book on the Elements for Physics.

The last lunch I had with Albert was in June 2009 discussing a common project with Total. We also talked about his recent visit to Chile and Easter Island. After his return from Easter Island he had a stroke in Chile and was then repatriated to France. I saw him 3 December; he passed away 6 December 2009. His contribution to inverse problem theory will remain alive forever.

### Roel Snieder's remarks on Albert Tarantola

Thank you for awarding Albert Tarantola the Maurice Ewing Medal, and thank you for asking me to receive this medal on his behalf. Albert's wife, Maria, is not able to be here, and I will make sure she receives Albert's Maurice Ewing Medal. Maria, we hold you in our thoughts tonight. You are with us in spirit for this moment as we celebrate the work of Albert.

I am truly humbled to be here in this role and feel like I am standing in shoes I cannot fill. Albert was a friend and colleague. He wrote two quotes in books that I would like to share with you because they shed light on Albert's character. When I worked with Albert in Paris, he discovered I had never studied general relativity. He muttered “c'est impossible,” went over to his bookshelf, took the book of Weinberg, and gave it to me after he wrote in it: “Rend mois le meme poids en retour, mais en idées” — return the same weight to me, but as ideas. Albert was a man of ideas. In fact, he mostly cared about ideas, and the more fundamental they were, the more important they were for him. And in my copy of his book Elements for Physics he wrote “Pour Roel, En souvenir d'une longue complicité intellectuelle,” for Roel, as a memory for a long intellectual complicity. This is what Albert loved, an intellectual complicity. It has been an honor for me to be part of Albert's intellectual world, which involved bold ideas and bold confrontations, all with the purpose of moving forward.

I will not attempt to give a laudation but instead will try to capture what I think Albert would have said tonight. Guessing what Albert would say is hazardous — he sometimes would change ideas at the spur of the moment — but this is my best guess of what Albert would say if he could accept the Maurice Ewing Medal in person.

He first would thank SEG and everybody who made this honor possible. Then he would thank Maria for her support over many years. Albert would recount how he started to work on what we now call full-waveform inversion in the 1980s as an outgrowth of his work on Bayesian statistics. He would tell us about starting the Equipe de Tomographie Géophysique in Paris, and what an exciting time it was with visitors who would come and go, and with gadgets like the connection machine — Albert loved gadgets. Albert would tell us that he realized in the 1990s that his dream of full-waveform inversion did not work, that he wanted to be honest, and that is why at the IUGG meeting in Vienna he had to get up in front of hundreds of people to tell them that he could not make his dream a reality. And then Albert would tell us about the amazing surprise that, around 2005, full-waveform inversion came back, that his vision became realized with the computers of that time, and how thrilled he was to see that happen. Albert would thank the people he worked with, the people he collaborated with and sparred with intellectually.

And then Albert would tell us that what he really wanted was to devise a theory that would change the world. Perhaps a theory where through the torsion of space-time one could explain the stability of the electron, or some bold theory like that.

There are a few things I want to tell you, Albert. You may not have changed our worldview in the way you wanted to, but without a doubt you have changed geophysics. And there is more I want to tell you, dear Albert. We love you. We love your brilliant mind. We love your lively and animated spirit. We love your unwavering courage to stand up for what you think is right. And we love the many moments of laughter that we have had with you.

## Notable publications

### Books

- Tarantola, Albert (2005).
*Inverse Problem Theory and Methods for Model Parameter Estimation*. Society for Industrial and Applied Mathematics (SIAM). ISBN 978-0-89871-572-9. - Tarantola, Albert (2006).
*Elements for Physics Quantities, Qualities, and Intrinsic Theories*. Springer Science+Business Media. ISBN 978-3-642-06452-4.

### Scientific articles

- Tarantola, Albert; Valette, Bernard (1982). "Inverse Problems = Quest for Information".
*Journal of Geophysics***50**: 159–170. - Tarantola, Albert; Valette, Bernard (May 1982). "Generalized Nonlinear Inverse Problems Solved Using the Least Squares Criterion".
*Reviews of Geophysics and Space Physics***20**: 219–232. doi:10.1029/RG020i002p00219. - Tarantola, Albert (October 1986). "A strategy for nonlinear elastic inversion of seismic reflection data".
*Geophysics***51**(10): 1893–1903. doi:10.1190/1.1442046. - Mosegaard, Klaus; Tarantola, Albert (1995). "Monte Carlo Sampling of Solutions to Inverse Problems".
*Journal of Geophysical Research***100**(B7): 12,431-12,447. doi:10.1029/94jb03097.

## References

- ↑ (2018). ”Honors and Awards.”
*The Leading Edge*, 37(11), 842–854. http://dx.doi.org/10.1190/tle37110842.1

## External links

- Honorable mention - Best Paper of
*Geophysics*(2011):*Quest for consistency, symmetry, and simplicity -- The legacy of Albert Tarantola,*Klaus Mosegaard - Albert Tarantola's web page