In 1962, Thomas S. Kuhn published the first edition of his now classic study on the structure of scientific revolutions. He divided scientists into those working on routine problems (the puzzle solvers) and those who create the new scientific paradigms which project an existing discipline into novel and unexpected trajectories. Leon Thomsen definitely belongs to this second category.
     Along with a distinguished group of his academic and industrial peers, Leon has literally added a new dimension to exploration seismology. I refer, of course, to the emerging field of stress wave propagation in anisotropic media. The ideas have been around since the days of Love and before, but Leon reworked the entire theory into a form easily adaptable to the needs of the applied geophysicist. Thanks to these efforts, we are now beginning to infer fracture direction and fracture intensity from multicomponent recordings. The presence of fractures in the reservoir often controls its permeability, and is thus of vital economic importance. This work has inspired much recent interest in reservoir geophysics, a technology which brings explorationists into
     much closer working contact with the reservoir engineer. It is therefore no exaggeration to say that Leon is one of those directly responsible for the redirection of our efforts toward the geophysical delineation of the reservoir. His anisotropy parameters "epsilon," "delta" and "gamma" have become household words in the technical literature their use so universal that hardly anybody bothers to define them anymore. At such a juncture it is both fitting and appropriate that
     the SEG honor Leon Thomsen with the Reginald Fessenden Award.
     Leon is a native of Tulsa, Oklahoma. His father, Erik Thomsen, had a distinguished career as an exploration geophysicist with Amoco. It was my privilege to know Erik years before I met his son, though Erik was happy to confine himself strictly to isotropic pursuits. Leon did his undergraduate work at Cal Tech, from where he graduated in geophysics in 1964. It is of interest to note that he was partially supported by an SEG scholarship money well spent, on hindsight! He then entered graduate school at Columbia and received his PhD from that august institution in 1969. After brief assignments at the Centre Nationale de la Recherche Scientifique in Paris, at Cal Tech in Pasadena, and at IBM in San Jose, California, he joined the faculty of the State University of New York at Binghamton. While there, he spent a sabbatical at the Australian National University in Canberra and was also a visitor at the Goddard Space Flight Center in New York. In 1980, Leon made the decision to abandon the academic life. He
     moved back to his native Tulsa to join Amoco's Research Center. His earlier work in rock physics enabled him to view the seismogram from the perspective of a materials scientist and it was this fortuitous circumstance that enabled Leon to establish some
     of the earliest links between multicomponent seismic data and fracture patterns in the reservoir rock. Aided and stimulated by related work by his colleagues both within Amoco and elsewhere, Leon was thus able to lay the foundation for the use of seismic anisotropy in exploration work today.
     It will come as no surprise that Leon has been and is a prolific publisher of his ideas. He is the author of several key publications, but perhaps the one that has had the greatest impact is his 1986 Geophysics paper entitled "Weak elastic anisotropy," in which he defined the three anisotropy parameters now commonly associated with his name. Leon is a gifted teacher and a lucid writer his prose is a pleasure to read. He has been a natural mentor for his younger colleagues at Amoco Research Center. Several industrial "postdocs" have worked with him in recent years, collaborations which have already produced important results. A good example is Leon's work with Dave Scott (now at University College, London) in the seismic prediction of pore pressure ahead of the drill. More recently, his research with Ilya Tsvankin (now at the Colorado School of Mines) has led to further insights into the behavior of anisotropic rocks.
     Leon has been an active participant in professional affairs. He has been a loyal member of the SEG Research Committee, where all of us have learned that he is not afraid to speak his mind when the need arises. He is keenly aware of the predicament that science faces in both the energy industry and the country at large and he has spoken out forcefully in defense of exploration research.
     It is said that behind every successful man there stands a woman, and Leon is no exception. His delightful wife, Pat, no doubt has done her share to contribute to Leon's success as a scientist. In Leon Thomsen, the Society of Exploration Geophysicists is rewarding one of the finest of our profession.

     Sven Treitel