TY - JOUR
T1 - The Effects of Shear Strain, Fabric, and Porosity Evolution on Elastic and Mechanical Properties of Clay-Rich Fault Gouge
AU - Kenigsberg, Abby R.
AU - Rivière, Jacques
AU - Marone, Chris
AU - Saffer, Demian M.
N1 - Funding Information:
We thank S. Swavely for the technical help in the laboratory; David C. Bolton, Srisharan Shreedharan, Parisa Shokouhi, and Charles Ammon for the key discussions; and two anonymous reviewers for the insightful input. We gratefully acknowledge support from the GDL Foundation, DOE geothermal program (DOE EERE DE‐EE0006762), and the NSF Geophysics program (NSF‐EAR award 1215856 to D.S. and EAR‐1520760 and EAR‐1547286/1547441 to C.M.). All data are available at Penn State ScholarSphere ( https://scholarsphere.psu.edu/ , specifically at https://doi.org/10.26207/977t‐mv11 , https://doi.org/10.26207/s0qc‐gw60 , https://doi.org/10.26207/71hz‐j207 , https://doi.org/10.26207/50by‐de04 , https://doi.org/10.26207/sqd0‐5929 ).
Funding Information:
We thank S. Swavely for the technical help in the laboratory; David C. Bolton, Srisharan Shreedharan, Parisa Shokouhi, and Charles Ammon for the key discussions; and two anonymous reviewers for the insightful input. We gratefully acknowledge support from the GDL Foundation, DOE geothermal program (DOE EERE DE-EE0006762), and the NSF Geophysics program (NSF-EAR award 1215856 to D.S. and EAR-1520760 and EAR-1547286/1547441 to C.M.). All data are available at Penn State ScholarSphere (https://scholarsphere.psu.edu/, specifically at https://doi.org/10.26207/977t-mv11, https://doi.org/10.26207/s0qc-gw60, https://doi.org/10.26207/71hz-j207, https://doi.org/10.26207/50by-de04, https://doi.org/10.26207/sqd0-5929).
PY - 2019/11/1
Y1 - 2019/11/1
N2 - The elastic and mechanical properties of fault gouge are key controls on fault zone stiffness, strength, damage, healing, and sliding stability. Clay minerals are prevalent in fault zones and have significant effects on friction, porosity, elastic properties, and shear fabric development. Although clay-rich gouges are well studied, the roles of porosity evolution and fabric formation in modulating elastic and mechanical properties are unclear. We have found that with progressive shear, the role of strain localization and fabric development may compete with densification to control the evolution of friction and elastic moduli. We report on a suite of double-direct shear experiments on synthetic gouge composed of 50% Ca-montmorillonite and 50% granular quartz at a normal stress of 25 MPa. We measure the coefficient of friction, porosity, P and S wave speeds, and bulk and shear moduli, and their evolution with shearing, to shear strains up to ~25. We find that the evolution of Vp, Vs, and elastic moduli are controlled by the interplay of porosity loss, shear fabric development, and particle contact stiffness. In general, Vp, Vs, and elastic moduli increase with shear strain and are accompanied by gradual densification and porosity loss. However, at intermediate shear strains (~2–8) a decrease in Vp, Vs, and elastic moduli is superimposed on this overall trend. Based on previous microstructural studies, we hypothesize that fabrics develop parallel to shear direction (perpendicular to wave propagation) over this range of strains, leading to reduced fault stiffness and competing with porosity loss as the dominant control on elastic properties.
AB - The elastic and mechanical properties of fault gouge are key controls on fault zone stiffness, strength, damage, healing, and sliding stability. Clay minerals are prevalent in fault zones and have significant effects on friction, porosity, elastic properties, and shear fabric development. Although clay-rich gouges are well studied, the roles of porosity evolution and fabric formation in modulating elastic and mechanical properties are unclear. We have found that with progressive shear, the role of strain localization and fabric development may compete with densification to control the evolution of friction and elastic moduli. We report on a suite of double-direct shear experiments on synthetic gouge composed of 50% Ca-montmorillonite and 50% granular quartz at a normal stress of 25 MPa. We measure the coefficient of friction, porosity, P and S wave speeds, and bulk and shear moduli, and their evolution with shearing, to shear strains up to ~25. We find that the evolution of Vp, Vs, and elastic moduli are controlled by the interplay of porosity loss, shear fabric development, and particle contact stiffness. In general, Vp, Vs, and elastic moduli increase with shear strain and are accompanied by gradual densification and porosity loss. However, at intermediate shear strains (~2–8) a decrease in Vp, Vs, and elastic moduli is superimposed on this overall trend. Based on previous microstructural studies, we hypothesize that fabrics develop parallel to shear direction (perpendicular to wave propagation) over this range of strains, leading to reduced fault stiffness and competing with porosity loss as the dominant control on elastic properties.
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U2 - 10.1029/2019JB017944
DO - 10.1029/2019JB017944
M3 - Article
AN - SCOPUS:85074830742
VL - 124
SP - 10968
EP - 10982
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - 11
ER -