Cinna Lomnitz

Cinna Lomnitz Aronsfrau (4 May 1925 – 7 July 2016) was a Chilean-Mexican geophysicist known for his contributions in the fields of rock mechanics and seismology.

Early life and education Lomnitz was born to a Jewish family in Cologne, Germany. He graduated as engineer from the University of Chile in 1948. He then studied with Karl von Terzaghi in Harvard University and obtained a Master's degree in soil mechanics.

Lomnitz received his doctorate from Caltech in 1955 with a dissertation on creep measurements in igneous rocks. Its principal thesis, a logarithmic creep behavior observed in rocks, was reformulated as the "Lomnitz Law" by Harold Jeffreys in 1958. The Lomnitz law is expressed as, where, is the time-varying creep (or, strain), is the constant stress load on the material, is the shear modulus, is a positive material constant, and is the creep constant. Though the Lomnitz law was inferred empirically from rheological measurements on rocks, its validity was firmly established by Pandey and Holm by deriving it from the physical principles in the framework of fractional calculus. They had used a time-varying Maxwell model in their analysis and found that the underlying physical mechanism in rocks that led to the Lomnitz law was a linearly time-varying viscosity, , where is the constant part of the viscosity and is the time-varying part of the viscosity, such that . Such a property with increasing viscosity with time corresponds to rheopecty, or anti-thixotropy, a special class of Non-Newtonian fluid. Pandey and Holm extracted the physical interpretation of the parameters of the Lomnitz law as follows: where, is the relaxation time during which the transition from the elastic- to creep-type deformation occurs.

Cinna Lomnitz died in Mexico City in 2016, aged 91.