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Title: Nonlinear softening of unconsolidated granular earth materials

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—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.
Authors:
ORCiD logo [1] ; ORCiD logo [2] ;  [3] ; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of Memphis, Memphis, TN (United States)
  3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of Nevada, Reno, NV (United States)
Publication Date:
Report Number(s):
LA-UR-17-26614
Journal ID: ISSN 2169-9313
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 122; Journal Issue: 9; Journal ID: ISSN 2169-9313
Publisher:
American Geophysical Union
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE Office of Science (SC); USDOE Laboratory Directed Research and Development (LDRD) Program
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Earth Sciences; Material Science; granular materials; softening; wave motion; resonance; nonlinear elasticity failure
OSTI Identifier:
1469541

Lieou, Charles Ka Cheong, Daub, Eric G., Guyer, Robert A., and Johnson, Paul Allen. Nonlinear softening of unconsolidated granular earth materials. United States: N. p., Web. doi:10.1002/2017JB014498.
Lieou, Charles Ka Cheong, Daub, Eric G., Guyer, Robert A., & Johnson, Paul Allen. Nonlinear softening of unconsolidated granular earth materials. United States. doi:10.1002/2017JB014498.
Lieou, Charles Ka Cheong, Daub, Eric G., Guyer, Robert A., and Johnson, Paul Allen. 2017. "Nonlinear softening of unconsolidated granular earth materials". United States. doi:10.1002/2017JB014498. https://www.osti.gov/servlets/purl/1469541.
@article{osti_1469541,
title = {Nonlinear softening of unconsolidated granular earth materials},
author = {Lieou, Charles Ka Cheong and Daub, Eric G. and Guyer, Robert A. and Johnson, Paul Allen},
abstractNote = {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—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.},
doi = {10.1002/2017JB014498},
journal = {Journal of Geophysical Research. Solid Earth},
number = 9,
volume = 122,
place = {United States},
year = {2017},
month = {8}
}