Elasticity: Stress and strain: BASIC SEISMOLOGY 3

E lasticity is the property that enables a fluid or solid body to resist change in size and shape when an external force is applied and to return to its original size and shape when the force is removed. This concept is a major building block in seismology because it is the elastic properties of rocks which allow seismic waves to propagate through the earth. The theory of elasticity is one of the major achievements of classical physics. Its architects include many of the colossal scientific figures of the 17th, 18th and 18th centuries, among whom are Robert Hooke, Gottfried Wilhelm Leibniz, James Bernoulli and his nephew Daniel Bernoulli, Leonhard Euler, Thomas Young, Charles Augustin Coulomb, Augustin Louis Cauchy, Claude Louis Marie Navier, Simeon Denis Poisson and George Gabriel Stokes. The framework, which they and others constructed to quantify and analyze elasticity, derives from the basic concepts of classical mechanics known as stress and strain and the mathematical linkage known as Hooke’s Law. Stresses are forces per unit area that are transmitted through a material, i.e., forces exerted by one part of a body on a neigbboring part. Stresses that act perpendicularly to a surface are