LOW-ANGLE NORMAL FAULT, PANAMINT VALLEY, CA.

We investigate the relationship between frictional strength and clay mineralogy of natural fault gouge from a low-angle normal fault in Panamint Valley, CA. Gouge samples were collected from the fault zone at five locations along a North-South transect of the rangebounding fault system, spanning a variety of bedrock lithologies. Samples were powdered and sheared in the double-direct shear configuration at room-temperature and humidity. The coefficient of friction, µ, was measured at a range of normal stresses from 5 MPa-150 MPa for all samples. Our results reinforce the intuitive understanding that natural fault gouge zones are inherently heterogeneous. Samples from a single location exhibit dramatic differences in behavior, yet all three were collected within a meter of the fault core. For most of the samples, friction varies from µ = 0.6-0.7, consistent with Byerlee’s law. However, samples with greater than 50 wt. % total clay content were much weaker (µ = 0.2-0.4). Expandable clay content of the samples ranged from 10 to 40 wt. %. Frictional weakness did not correlate with expandable clays. Our results indicate that friction decreases with increasing total clay content, rather than with the abundance of expandable clays. The combination of field relations, analytical results, and friction measurements indicate a correlation between clay content, fabric intensity and localization of strain in the fault core. A micromechanical model is suggested for weakening of fault gouge composed of mixed clay and granular material. We provide broad constraints on the depth of gouge generation and the depth at which fault weakness initiates. We hypothesize that slip on the Panamint Valley fault and similar low-angle normal faults is mechanically feasible in the mid-upper crust if the strength of the fault is limited by weak, clay-rich fault gouge.

[1]  F. Chester,et al.  Fracture surface energy of the Punchbowl fault, San Andreas system , 2005, Nature.

[2]  J. Anthony,et al.  Influence of particle characteristics on granular friction , 2005 .

[3]  J. Brune,et al.  Particle size and energetics of gouge from earthquake rupture zones , 2005, Nature.

[4]  K. Livi,et al.  Magnetic and clast fabrics as measurements of grain-scale processes within the Death Valley shallow crustal detachment faults , 2004 .

[5]  D. Lockner,et al.  Crystallographic controls on the frictional behavior of dry and water-saturated sheet structure minerals , 2004 .

[6]  C. Marone,et al.  Comparison of smectite- and illite-rich gouge frictional properties: application to the updip limit of the seismogenic zone along subduction megathrusts , 2003 .

[7]  T. Cladouhos,et al.  Structural geology and kinematic history of rocks formed along low-angle normal faults, Death Valley, California , 2003 .

[8]  A. Kopf,et al.  Compositional and Fluid Pressure Controls on the State of Stress on the Nankai Subduction Thrust , 2003 .

[9]  J. Knott,et al.  Quaternary low-angle slip on detachment faults in Death Valley, California , 2003 .

[10]  Karen Mair,et al.  Influence of grain characteristics on the friction of granular shear zones , 2002 .

[11]  R. Sibson,et al.  Normal faults, normal friction? , 2001 .

[12]  P. Vrolijk,et al.  The dating of shallow faults in the Earth's crust , 2001, Nature.

[13]  K. Mair,et al.  Laboratory results indicating complex and potentially unstable frictional behavior of smectite clay , 2001 .

[14]  J. Mutter,et al.  Evidence for fault weakness and fluid flow within an active low-angle normal fault , 2001, Nature.

[15]  Marek Cichanski Low-angle, range-flank faults in the Panamint, Inyo, and Slate ranges, California: Implications for recent tectonics of the Death Valley region , 2000 .

[16]  Daniel M. Mueth,et al.  Signatures of granular microstructure in dense shear flows , 2000, Nature.

[17]  D. Lockner,et al.  The effect of mineral bond strength and adsorbed water on fault gouge frictional strength , 2000 .

[18]  N. Snyder,et al.  Depositional and tectonic evolution of a supradetachment basin: 40Ar/39Ar geochronology of the Nova Formation, Panamint Range, California , 2000 .

[19]  M. Murphy,et al.  Range-front fault scarps of the Sierra El Mayor, Baja California: Formed above an active low-angle normal fault? , 1999 .

[20]  J. Morgan,et al.  Numerical simulations of granular shear zones using the distinct element method: 1. Shear zone kinematics and the micromechanics of localization , 1999 .

[21]  Julia K. Morgan,et al.  Numerical simulations of granular shear zones using the distinct element method: 2. Effects of particle size distribution and interparticle friction on mechanical behavior , 1999 .

[22]  C. Marone LABORATORY-DERIVED FRICTION LAWS AND THEIR APPLICATION TO SEISMIC FAULTING , 1998 .

[23]  Carolyn Z. Mutter,et al.  Shallow dips of normal faults during rapid extension: Earthquakes in the Woodlark‐D'Entrecasteaux rift system, Papua New Guinea , 1997 .

[24]  B. Wernicke Low-angle normal faults and seismicity: A review , 1995 .

[25]  D. Hill,et al.  Fault orientations in extensional and conjugate strike-slip environments and their implications , 1991 .

[26]  D. B. Slemmons,et al.  Right‐lateral displacements and the Holocene slip rate associated with prehistoric earthquakes along the Southern Panamint Valley Fault Zone: Implications for southern Basin and Range tectonics and Coastal California deformation , 1990 .

[27]  C. Scholz The Mechanics of Earthquakes and Faulting , 1990 .

[28]  Robert C. Reynolds,et al.  X-Ray Diffraction and the Identification and Analysis of Clay Minerals , 1989 .

[29]  B. Wernicke,et al.  On the role of isostasy in the evolution of normal fault systems , 1988 .

[30]  S. Biehler A geophysical investigation of the Northern Panamint Valley, Inyo County, California: Evidence for possible low‐angle normal faulting at shallow depth in the crust , 1987 .

[31]  B. Burchfiel,et al.  Geology of Panamint Valley ‐ Saline Valley Pull‐Apart System, California: Palinspastic evidence for low‐angle geometry of a Neogene Range‐Bounding Fault , 1987 .

[32]  C. Scholz Wear and gouge formation in brittle faulting , 1987 .

[33]  A. Ruina Slip instability and state variable friction laws , 1983 .

[34]  J. Byerlee,et al.  Strain Hardening and Strength of Clay-Rich Fault Gouges , 1982 .

[35]  P. R. Vaughan,et al.  The drained residual strength of cohesive soils , 1981 .

[36]  J. Byerlee Friction of rocks , 1978 .

[37]  J. Handin,et al.  On the Coulomb‐Mohr failure criterion , 1969 .

[38]  H. Rietveld A profile refinement method for nuclear and magnetic structures , 1969 .

[39]  B. Burchfiel,et al.  “PULL-APART” ORIGIN OF THE CENTRAL SEGMENT OF DEATH VALLEY, CALIFORNIA , 1966 .

[40]  C. R. Longwell Low‐angle normal faults in the basin‐and‐range province , 1945 .

[41]  G. Axen Mechanics of Low-Angle Normal Faults , 2003 .

[42]  C. Dengo,et al.  Chapter 2 Fabrics of Experimental Fault Zones: Their Development and Relationship to Mechanical Behavior , 1992 .

[43]  K. Hodges,et al.  Chapter 19: Structural unroofing of the central Panamint Mountains, Death Valley region, southeastern California , 1990 .

[44]  J. Jackson,et al.  Normal faulting in the upper continental crust: observations from regions of active extension , 1989 .

[45]  R. C. Reynolds,et al.  The Thermal Transformation of Smectite to Illite , 1989 .

[46]  F. Chester,et al.  Composite planar fabric of gouge from the Punchbowl Fault, California , 1987 .

[47]  N. Yoshioka FRACTURE ENERGY AND THE VARIATION OF GOUGE AND SURFACE ROUGHNESS DURING FRICTIONAL SLIDING OF ROCKS , 1986 .

[48]  Frederick M. Chester,et al.  Implications for mechanical properties of brittle faults from observations of the Punchbowl fault zone, California , 1986 .

[49]  A. Lachenbruch,et al.  9: Models of an extending lithosphere and heat flow in the Basin and Range province , 1978 .

[50]  K. Terzaghi,et al.  Soil mechanics in engineering practice , 1948 .