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Russian Geology and Geophysics

2006 year, number 5


V.Yu. Zaitsev and L.A. Matveev*
Institute of Applied Physics, 46 ul. Ul'yanova, Nizhny Novgorod, 603600, Russia
* Nizhny Novgorod University, 23 prosp. Gagarina, Nizhny Novgorod, 603950, Russia
Keywords: Microinhomogeneous medium, elastic nonlinearity, linear dissipation, amplitude dependent dissipation
Pages: 694-709


We discuss a mechanism of nonhysteretic strain-amplitude dependent dissipation of elastic waves in microinhomogeneous media containing linearly dissipative and nonlinear elastic soft defects. The combined effect of these factors can cause well-pronounced essentially dissipative nonlinearity of elastic waves. The mechanism presumably works in rocks and other materials with microstructure where cracks and grain contacts act as soft inclusions. Unlike homogeneous materials where strain dependent variations of dissipation and elasticity are commonly of the same order, dissipation variations in microinhomogeneous materials can be times as great as the respective elasticity variations. A slight (a few percent) change in Young's modulus can correspond to a manifold dissipation change at moderate strain typical of acoustic and seismic applications. Moreover, in the case of variable frequency, this nonlinear mechanism can increase or decrease Young's modulus or reduce its variation to zero at certain frequencies while dissipation variations remain quite large. The nonhysteretic mechanism may act concurrently with hysteretic mechanisms, which are due to friction and adhesion effects and are commonly invoked for materials with microstructure, and influence the relationship between strain dependent dissipation and elasticity observed in experiments on nonlinear dissipative effects.