Nonlinear softening of unconsolidated granular earth materials
| Autor: | Paul A. Johnson, Charles K. C. Lieou, Robert A. Guyer, Eric G. Daub |
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| Rok vydání: | 2017 |
| Předmět: |
Materials science
010504 meteorology & atmospheric sciences Modulus Mechanics Particle displacement Granular material 01 natural sciences Seismic wave Geophysics Space and Planetary Science Geochemistry and Petrology Fault gouge Nonlinear resonance 0103 physical sciences Earth and Planetary Sciences (miscellaneous) Geotechnical engineering 010306 general physics Elastic modulus Softening 0105 earth and related environmental sciences |
| Zdroj: | Journal of Geophysical Research: Solid Earth. 122:6998-7008 |
| ISSN: | 2169-9313 |
| Popis: | Unconsolidated granular earth materials exhibit softening behavior due to external perturbations such as seismic waves; namely, the wave speed and elastic modulus decrease upon increasing the strain amplitude above dynamics strains of about 10−6 under near-surface conditions. In this letter, we describe a theoretical model for such behavior. The model is based on the idea that shear transformation zones (STZs) – clusters of grains that are loose and susceptible to contact changes, particle displacement, and rearrangement – are responsible for plastic deformation and softening of the material. We apply the theory to experiments on simulated fault gouge composed of glass beads, and demonstrate that the theory predicts nonlinear resonance shifts, reduction of the P-wave modulus, and attenuation, in agreement with experiments. The theory thus offers insights on the nature of nonlinear elastic properties of a granular medium, and potentially into phenomena such as triggering on earthquake faults. |
| Databáze: | OpenAIRE |
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