Frictional heating on a fault zone with finite thickness

Summary. The problem of frictional heating on a fault of finite thickness is considered. Temperature distributions during and after faulting are obtained for faults of various thicknesses. A thick fault approximation is shown to be valid if a fault has a thickness greater than about 1 cm. The thickness of the melted zone is predicted for various frictional stress levels and displacements. The predicted thicknesses are shown to be in reasonable agreement with field observations.     

A back-of-the-envelope approach to boudinage mechanics

Smith has shown from linear hydrodynamic stability that pinch-and-swell boudinage is possible only in a non-Newtonian material. By assuming uniaxial stress and strain and large viscosity contrast between the competent layer and the incompetent matrix, Smith's result can be derived in a very simple way. The one-dimensional force balance also predicts growth rates, although not dominant wavelengths. However, we question the ability of even linear stability analysis to accurately predict boudin widths.     

A fluid model for the shape of accretionary wedges

In this paper the accretionary wedges landward of most oceanic trenches are modelled assuming a Newtonian fluid rheology.It is shown that lubrication theory is applicable and that the addition of material to the wedges can be neglected in determining the shape of the wedges. The predicted shape of the wedges is in good agreement with bathymetric profiles across the Kurile, Ryukyu and Aleutian wedges. From the shape of the above wedges, it is deduced that accretionary sediments have viscosities between 10¹⁸ and 10¹⁹ poise.     

On the statistical mechanics of distributed seismicity

In order to understand the underlying physics of distributed seismicity better we have considered a 2-D array of slider blocks connected by springs and interacting via static friction with a surface. There is no driving plate in this model. The time evolution of the system is found from numerical simulations in a cellular automata formulation. Energy is conserved and is the single control parameter. The distribution of energies in the springs is found to obey a modified Maxwell-Boltzmann statistics. It is found that the number-size statistics of clusters of unstable sliding blocks is identical to those in percolation clusters in the site-to-site percolation model. There is a well-defined critical point when unstable blocks become connected across the array. It has been previously suggested that distributed seismicity in a seismic zone is the percolation backbone of a 3-D percolation cluster. The fact that low-level seismicity satisfies the Gutenberg-Richter frequency-magnitude relation and is nearly constant in time also suggests that this background seismicity is similar to thermally induced noise.