Abstract. A number of observations indicate that an upper stability transition occurs along well-developed faults, such as the San Andreas, as a result of unconsolidated gouge within shallow regions of these faults. These observations include the depth distribution of seismicity along faults with and without well-developed gouge zones, correlations between seismicity and shallow crustal structure, and modeling of coseismic and post-seismic slip. In addition, recent experimental friction studies indicate that thick layers of simulated gouge exhibit a positive slip-rate dependence of frictional resistance (velocity strengthening) and thus inherently stable slip, whereas bare rock surfaces and thin gouge layers exhibit potentially unstable velocity weakening behavior. Subduction zones with large accretionary wedges also exhibit an upper stability transition in that slip is aseismic within the accretionary wedge. A stability transition due to the presence of unconsolidated material can also be invoked in this case.

The roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep. We have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 -5 to 1 m. using field and laboratory scale profilimeters.

No abstract

No abstract