Discussion

Abstract

A. Whittaker writes: My comments on the paper presented by Muir Wood and Mallard are partly about the scientific concepts and arguments advanced, but also about semantics. I find the concept of the ‘current tectonic regime’ to be useful. It is certainly to be preferred, in the consideration of whether or not a fault is active, to criteria based simply upon some arbitrarily-decided, extrinsic time period. However, I wonder whether the term ‘current tectonic regime’ is the most appropriate. The authors concede that the ‘current tectonic regime’ can only be described by its manifestations, i.e. observation of the stresses and strains within the Earth’s crust. Would it not be more informative to the non-specialist to make it explicit and clear that, essentially, it is crustal stress that is being referred to? A similar concept was advanced at the Society’s meeting on neotectonics held in 1984 (Hancock & Williams 1986). At this meeting Hancock, in discussion of the temporal scope of neo- tectonics, suggested that the selection of an arbitrary Neogene or Quaternary date to be applied globally for the beginning of the period during which neotectonic structures form, is unhelpful. He brought forward the alternative notion that for a given region the neotectonic phase could be thought of as having begun when the present day disposition of relevant plate boundaries (and their associated motions) was estab- lished. A suggestion to modify this proposal was made by Blen- kinsop (Hancock & Williams 1986). It was to the effect that the neotectonic