Open AccessReply to comment by S. H. Lamb on ‘Deformation of the NE Basin and Range Province: the response of the lithosphere to the Yellowstone plume?’ by R. Westaway
Author(s) -
Westaway Rob
Publication year - 1991
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1991.tb05710.x
Subject(s) - geology , lithosphere , basin and range topography , vorticity , geometry , shear (geology) , oblique case , slip (aerodynamics) , seismology , basin and range province , orientation (vector space) , simple shear , geodesy , pure shear , counterexample , mathematics , mathematical analysis , physics , mechanics , tectonics , vortex , thermodynamics , combinatorics , petrology , linguistics , philosophy
(i) Lamb’s (1991) first point is incorrect. Conditions exist whereby a single set of faults can take up distributed simple shear and extensional pure shear and where the strain rate tensor is uniaxial (see Westaway 1991). Whether faults in any set that satisfies these conditions take up pure normal slip or oblique slip simply depends on their orientation relative to the local extension direction. (ii) Lamb (1991) correctly states that equation (2.19) of Westaway (1989) does not correctly describe slip sense on faults during uniaxial extension where vertical vorticity is non-zero. Westaway (1991) has indeed already shown this. Westaway (1991) has also developed appropriate new theory and has applied this theory to the NE Basin and Range Province. (iii) Westaway’s (1989) result that rotation rate around a vertical axis, o, of elongated blocks equals half the local vertical vorticity, xz, is correct for vorticity associated with concentric flow (an important special case) but is not correct in general. Lamb (1991) illustrates this point with two counterexamples that have already been noted by Westaway (1991). However, the orientation of active faults in the NE Basin and Range Province corresponds to neither of these counterexamples. Given this, x z / 2 remains a reasonable approximate estimate for w in the absence of any clear general method for obtaining a better estimate.