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Title: Slow dynamics and strength recovery in unconsolidated granular earth materials: a mechanistic theory

Abstract

Rock materials often display long-time relaxation, commonly termed aging or “slow dynamics”, after the cessation of acoustic perturbations. In this paper, we focus on unconsolidated rock materials and propose to explain such nonlinear relaxation through the Shear-Transformation-Zone (STZ) theory of granular media, adapted for small stresses and strains. The theory attributes the observed relaxation to the slow, irreversible change of positions of constituent grains, and posits that the aging process can be described in three stages: fast recovery before some characteristic time associated with the subset of local plastic events or grain rearrangements with a short time scale, log-linear recovery of the elastic modulus at intermediate times, and gradual turnover to equilibrium steady-state behavior at long times. Here we demonstrate good agreement with experiments on aging in granular materials such as simulated fault gouge after an external disturbance. These results may provide insights into observed modulus recovery after strong shaking in the near surface region of earthquake zones.

Authors:
ORCiD logo [1]; ORCiD logo [2]; ORCiD logo [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of Memphis, Memphis, TN (United States). Center for Earthquake Research and Information
Publication Date:
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
OSTI Identifier:
1394978
Report Number(s):
LA-UR-17-24249
Journal ID: ISSN 2169-9313
Grant/Contract Number:
AC52-06NA25396
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 122; Journal Issue: 10; Journal ID: ISSN 2169-9313
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Earth Sciences; Material Science

Citation Formats

Lieou, Charles Ka Cheong, Daub, Eric G., Ecke, Robert E., and Johnson, Paul A. Slow dynamics and strength recovery in unconsolidated granular earth materials: a mechanistic theory. United States: N. p., 2017. Web. doi:10.1002/2017JB014131.
Lieou, Charles Ka Cheong, Daub, Eric G., Ecke, Robert E., & Johnson, Paul A. Slow dynamics and strength recovery in unconsolidated granular earth materials: a mechanistic theory. United States. doi:10.1002/2017JB014131.
Lieou, Charles Ka Cheong, Daub, Eric G., Ecke, Robert E., and Johnson, Paul A. Fri . "Slow dynamics and strength recovery in unconsolidated granular earth materials: a mechanistic theory". United States. doi:10.1002/2017JB014131.
@article{osti_1394978,
title = {Slow dynamics and strength recovery in unconsolidated granular earth materials: a mechanistic theory},
author = {Lieou, Charles Ka Cheong and Daub, Eric G. and Ecke, Robert E. and Johnson, Paul A.},
abstractNote = {Rock materials often display long-time relaxation, commonly termed aging or “slow dynamics”, after the cessation of acoustic perturbations. In this paper, we focus on unconsolidated rock materials and propose to explain such nonlinear relaxation through the Shear-Transformation-Zone (STZ) theory of granular media, adapted for small stresses and strains. The theory attributes the observed relaxation to the slow, irreversible change of positions of constituent grains, and posits that the aging process can be described in three stages: fast recovery before some characteristic time associated with the subset of local plastic events or grain rearrangements with a short time scale, log-linear recovery of the elastic modulus at intermediate times, and gradual turnover to equilibrium steady-state behavior at long times. Here we demonstrate good agreement with experiments on aging in granular materials such as simulated fault gouge after an external disturbance. These results may provide insights into observed modulus recovery after strong shaking in the near surface region of earthquake zones.},
doi = {10.1002/2017JB014131},
journal = {Journal of Geophysical Research. Solid Earth},
number = 10,
volume = 122,
place = {United States},
year = {Fri Sep 08 00:00:00 EDT 2017},
month = {Fri Sep 08 00:00:00 EDT 2017}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on September 8, 2018
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