Frictional Constitutive Behavior of Natural Fault Gouge Materials: Effects of Mineralogy

Saffer EAR-0229585

Defining physical and mechanical properties of fault gouge and their

relationship to fault behavior remains a fundamental step toward

understanding earthquakes and faulting. Frictional velocity

dependence is considered the most likely mechanism to explain

differences between stable sliding (aseismic) and unstable stick-slip

(seismogenic) behavior. Materials that exhibit velocity-strengthening

behavior produce only inherently stable frictional slip, whereas

those that exhibit velocity-weakening are capable of hosting unstable

rupture. This work will define the frictional properties of a suite

of natural and synthetic mixed-mineralogy gouges, as a function of

composition. The experimental plan will focus on testing (1) natural

samples of subduction zone materials that have undergone progressive

alteration at temperatures up to ~250 degrees C, and (2) a suite of

synthetic mixtures of montmorillonite, illite, and quartz, and

developing the appropriate constitutive equations to describe their

behavior. This work will include: (1) quantitative x-ray diffraction

(XRD) to determine the composition of natural gouges, (2) a series of

shearing experiments for each material, over a wide range of

experimental conditions, and (3) petrographic and SEM

characterization of microstructures in experimentally deformed gouges

and comparison with natural microstructures observed in the sample

localities. The work will provide high-quality measurements of

frictional constitutive properties for realistic natural fault gouge

materials relevant to seismic faulting, and define variations in

these properties with gouge composition. This work will constitute an

important step toward a better understanding of fault behavior and

its potential variability with depth and along-strike. In addition,

detailed characterization of fabric development in experimentally

deformed gouges will provide important insights into application of

laboratory measurements to natural faults.