Carolyn Boulton - PhD Summary

Faults accommodate strain in the Earth’s crust either by creeping aseismically or by rupturing seismically. Near the Earth’s surface, fault slip commonly occurs on thin (mm-cm) surfaces composed of granular fault gouge. The frictional behaviour of fault gouge may govern whether faults creep or rupture. Through laboratory experiments and microstructural analyses, this research aims to assess the frictional strength and seismic behaviour of fault gouge formed within New Zealand rocks.

A custom-built annular shear apparatus (rheometer) in the Department of Geological Sciences can shear fault gouge at velocities experienced during earthquake slip (~1 ms-1). Initial experiments have succeeded in creating fault gouge under normal loads of 10 MPa; crushing, melting, and acoustic emissions accompanied fault gouge creation. Future experiments will measure the frictional resistance to shear and constrain the normal loads at which fault gouge weakens during high-velocity sliding.

Experiments in the rheometer will produce fault gouge with microstructures formed at known sliding velocities and strain rates. Comparison of these experimentally produced fault gouges with those collected from natural exposures of the Alpine Fault will provide new insights into the nature of faulting and strain accommodation along this seismically active plate boundary. These experiments have important implications for understanding seismic efficiency and estimating rupture top depth, a seismic engineering parameter.