In Memory of Ari Ben-Menachem

Ari Ben-Menachem

(1928 - 2026)

We mourn the passing of Professor Ari Ben-Menahem on April 9, 2026. A Professor of Geophysics at the Weizmann Institute of Science (WIS), he was a pioneering seismologist, a prolific author, a polymath, and a distinguished historian of science whose work shaped generations of researchers and students.

Born in Berlin on November 4, 1928, Prof. Ben-Menahem earned an M.Sc. in Physics from the Hebrew University of Jerusalem (1954) and a Ph.D. from the California Institute of Technology (1961). He continued at Caltech for postdoctoral research, working with Hugo Benioff and Frank Press (1962-1965), before joining the Weizmann Institute, where he built an internationally recognized program in seismology and geophysics.

His doctoral work helped establish modern seismic-source electrodynamics, advancing the theory of wave radiation from finite rupturing faults. Among the foundational ideas he introduced were the concepts of directivity and potency, which contributed to the development and interpretation of the seismic moment tensor. These contributions continue to underpin how rupture processes and earthquake source parameters are inferred from recorded seismic waveforms.

Prof. Ben-Menahem's scholarship extended well beyond earthquake source theory. In 1975, he analyzed seismic and barometric records of the Tunguska event (June 30, 1908) to estimate the height and energy of the explosion, offering one of the earliest feasible non-cometary mechanisms for this extraordinary extraterrestrial encounter.

A testament to his extraordinary breadth was his six-volume Historical Encyclopedia of Natural and Mathematical Sciences (Springer, 2009)—a monumental 6,000-page work tracing the evolution of ideas across the sciences and mathematics through biographies, essays, and historical context.

The Encyclopedia skillfully combines scholarly detail with broad historical perspective, revealing who influenced science, when they did so, what was achieved, and how these discoveries changed our view of nature.

Colleagues and former students remember Prof. Ben-Menahem for his intellectual generosity, high standards, and curiosity across disciplines. His legacy endures in the scientific tools he developed, the questions he inspired, and the people he influenced through teaching and writing.

We extend our heartfelt condolences to Prof. Ben-Menahem’s family, friends, colleagues, and students. May his memory be a blessing.