AMOS M. NUR (1938-2024)

BY MARK ZOBACK

AMOS MICHAEL NUR, Wayne Loel Professor of Earth Sciences, emeritus, at Stanford University, pioneer of rock physics, and leader of modern geophysics, died in his home office at Stanford on June 10, 2024.

Amos was born in Haifa, Israel, on Feb. 9, 1938, shortly after his parents, Zwi Hermann Nordheimer and Judith Herta Weiser, moved to Israel from Leipzig, Germany. He earned a B.S. in geology from Hebrew University in Jerusalem. After briefly studying at ETH in Zürich and receiving his Ph.D. in geophysics from MIT in 1969, he joined the Stanford faculty in 1970. To his many advisees, Amos was a creative and original thinker, as well as an inspirational advisor with a broad range of interests. He encouraged and celebrated student creativity and self-confidence. Over the course of his career, he advised 50 doctoral students and 25 master’s students.

Early in his career, Amos conducted laboratory studies on how applied stress affects the velocity of seismic waves traveling through rock. He discovered that applied stress induces seismic anisotropy — a directional variation in velocity — which led to the recognition that shear waves could be used to probe crustal stress. He further demonstrated that shear-wave splitting occurs when shear waves traveling through the earth’s crust are polarized into a fast shear wave, followed by a slow shear wave with orthogonal polarization. Building on studies of fluid effects on rock properties, Amos pioneered the use of seismic velocity measurements to monitor the evolution of oil and gas reserves before, during, and after development.

Throughout his career, his research focused on advancing a fundamental understanding of seismic data through both laboratory and theoretical studies. Through innovative experiments, theoretical advances, practical demonstrations, and a healthy dose of evangelism, he helped transform rock physics from a niche discipline into a central part of modern geophysics. He was widely recognized for promoting the computational modeling of rock properties — also known as digital rock physics — and for advancing the application of rock physics to four-dimensional (4D) seismic imaging. More than 30 years ago, he authored a seminal paper advocating for 4D seismic imaging, a data acquisition procedure that has since become critical in geophysical research. He was among the first to propose the dilatancy/diffusion hypothesis to explain reported seismic anomalies observed in the former Soviet Union. Reports suggested that just before large earthquakes occurred, there were measurable decreases in compressional seismic wave velocity, followed by a recovery of wave velocity. Amos hypothesized that as an earthquake approaches, increasing stress would first cause dilatancy — the formation of microcracks near the impending earthquake. Because these rapidly opened microcracks would be dry, there would be a temporary decrease in seismic velocity due to reduced pore pressure. As fluid diffusion into the microcracks occurs, fluid pressure would recover, seismic velocity would return to its initial value, and the earthquake would be triggered. While his hypothesis was well-supported by laboratory experiments, the wave speed variations reported by Soviet scientists could not be validated or replicated elsewhere.

Amos also studied large-scale tectonic questions, including the origin of back-arc and pull-apart basins. Using a simple physical model, he demonstrated how crustal block rotations could explain the seemingly complex coexistence of compressional, extensional, and strike-slip faults within the same geographic region. Along with earth scientist Zvi Ben-Avraham, Amos controversially hypothesized that fragments from the lost-continent of Pacifica explain how unusual crustal blocks were accreted to the continents surrounding the Pacific Basin. During the latter part of his career, he spoke extensively on the topic of oil and war, focusing on the intricate relationships between and among petroleum supply, national security, and international conflict.

Amos was a member of the National Academy of Sciences delegation to the People’s Republic of China in 1976, partly due to his work on the dilatancy/diffusion hypothesis since Chinese seismologists at the time were actively pursuing earthquake prediction. He served on the Seismology Committee of the National Research Council (1974-77), the Advisory Board of the National Science Foundation (1974-77), and the Hydrocarbon Research Committee of the National Research Council (1987-88).

Throughout his career, Amos earned a number of prestigious awards. In 1974, he received the American Geophysical Union’s Macelwane Medal, recognizing early-career contributions to Earth and space science. That same year, he was awarded the Newcomb Cleveland Prize from the American Association for the Advancement of Science for the paper he presented at the AAAS annual meeting, “Origin of Velocity Changes before Earthquakes: The Dilatancy Diffusion Hypothesis and Its Confirmation.” In 1991, he won the Silver Apple Award at the National Educational Film and Video Festival for his documentary The Walls Came Tumbling Down, which combined archaeological, geophysical, historical, and biblical evidence to explore the role of earthquakes in ancient civilizations. In 2011, in recognition of his lifetime contributions to rock physics, he received the Maurice Ewing Medal, the highest honor from the Society of Exploration Geophysicists. In 2013, the University of Haifa awarded him an honorary doctor of philosophy. Amos was an elected fellow of the American Geophysical Union, the Geological Society of America, and the California Academy of Sciences. A frequent invited speaker, he lectured at universities worldwide.

Amos published more than 250 peer-reviewed papers and authored three books. A highly original 1975 paper proposed the melt squirt hypothesis, suggesting that the pore-scale flow of partial melt could explain the viscoelastic behavior of Earth’s asthenosphere. His paper on critical porosity led to the development of quantitative tools for determining the elastic properties of oil and gas reservoirs. His subsequent stiff sand and soft sand models became essential tools for rock physics analyses of reservoirs and aquifers. Two of his seminal papers investigated the effects of porosity and clay content in sedimentary rocks, forming the foundation of rock physics principles applied to oil and gas reservoirs. His best-known book, Apocalypse: Earthquakes, Archaeology, and the Wrath of God (2008, co-authored with Dawn Burgess, Princeton University Press), argued that biblical accounts, mythology, and the archaeological record contain clues that ancient civilizations were destroyed by earthquakes rather than solely by wars.

He founded the Stanford Rock and Borehole Geophysics industrial affiliates consortium as well as the Stanford Center for Earth Resources Forecasting. These industrial consortia demonstrated the mutual benefits of academia and industry collaborations and highlighted the importance of fundamental research in solving real-world challenges. He also co-founded two successful companies, Petrophysical Services Inc. (1984), which performed special core analysis services for the oil and gas industry, and Ingrain (2008), which utilized digital rock physics technology — based on 3D micro-CT and FIB-SEM imaging — to calculate complex rock properties.

In addition to his research and teaching, Amos served, from 2000 to 2005, as director of the Stanford Bing Overseas Studies Program. This program provides transformational educational experiences in stimulating global settings. One undergraduate participant wrote to Amos: “You changed the way I look at everything — the world, my life, my education — what more can I say?” He was the first scientist to lead the program and made a profound impact by founding new academic opportunities, including a program in Australia focused on the Great Barrier Reef.

Amos is survived by his wife, Francina Lozada-Nur of Stanford, California; his son, Boaz Nur of Barcelona, Spain; and three grandchildren, Sofia, Sebastian, and Olivia Nur, all of Barcelona.