A scientific paper written 39 years ago by UH research professor Leon Thomsen holds the current record for the most citations in geophysics. The paper, titled 鈥淲eak Seismic Anisotropy,鈥� was published in 1986 in the journal Geophysics and has been cited 6,435 times in other scientific publications, according to data compiled in June 2025.
The paper developed a series of equations to describe weak anisotropy in materials, which was a state of bulk elastic media that had been recognized by previous workers but had not been simplified into a series of equations prior to this 1986 publication. In the early 1980s, most geophysicists understood the term 鈥渁nisotropy鈥� to mean polar anisotropy, because of the layered structure of sedimentary rocks. But the presence of oriented fractures in the subsurface removes the azimuthal symmetry and invalidates the assumption. Such fractured reservoirs may be detected from the surface using various seismic signatures of azimuthal anisotropy.
These observations were made by Thompson and colleagues at Amoco in the early 1980s but not released to the public until the Thompson publication was submitted in 1985 and published in 1986. Since that time, these ideas on weak anisotropy have become implemented throughout the oil industry, especially since wide-azimuth marine acquisition has become feasible. This concept of weak anisotropy remains central to research on shale gas prospects since the shales are seismically and hydraulically anisotropic.
鈥淟eon鈥檚 1986 paper is a milestone,鈥� said Dr. Yingcai Zheng, a professor of geophysics in the Department of Earth and Atmospheric Sciences. 鈥淗e discovered delta, or weak anisotropy, which lights up the darkness. It鈥檚 like F=ma鈥攆orce equals mass times acceleration鈥攆or physicists. Many people use this concept without citing it. The real impact of the paper is much greater than the number of citations.鈥�
Dr. Robert Stewart, director of the Allied Geophysical Lab in UH鈥檚 Department of Earth and Atmospheric Sciences, also praised Thomsen鈥檚 contributions. 鈥淒r. Thomsen not only discovered a compelling approximation to a complex elastic equation鈥攚hich describes a wide variety of rock types鈥攈e has tirelessly and clearly taught its theory and application to students and industry practitioners alike,鈥� Stewart said.
Thomsen completed his BS in geophysics from Caltech in 1964 and his PhD at Columbia University in 1969. Following his PhD, he was a tenured professor of geophysics at State University of New York at Binghamton, followed by a senior research position with BP-Amoco from 1980 to 2008, where he completed the work on weak anisotropy in 1986. Since 2008, he has served as a Research Professor of Exploration Geophysics in the 葫芦影业鈥檚 Department of Earth and Atmospheric Sciences. His recent research focuses on anisotropy and poroelasticity, which refers to how a porous rock鈥檚 elastic properties depend on the compressibility of its pore fluid.