  We assess if a characteristic length for a non-linear interfacial slip
instability follows from theoretical descriptions of sliding friction. We
examine friction laws and their coupling with the elasticity of bodies in
contact and show that such a length does not always exist. We consider a range
of descriptions for frictional strength and show that the area needed to
support a slip instability is negligibly small for laws that are more faithful
to experimental data. This questions whether a minimum earthquake size exists
and shows that the nucleation phase of dynamic rupture contains discriminatory
information on the nature of frictional strength evolution.
