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Fault trace geometry within the San wrench tectonics. Bull. Am. Ass. Petrol. Geol. 57, 74--96. Andreas and Calaveras Fault Zones--A clue to the YEATS, R. S. 1973. Newport Inglewood fault zone, Los evolution of some transcurrent fault zones. In: KovAc8, Angeles basin California. Bull. Am. Ass. Petrol. Geol. R. L. & NUR, A. (eds) Proc. of Con]. on Tectonic 57, 117-35. Problems of the San Andreas Fault System. Stanford Univ. Pub., Geol. Sci., 13, 251-8. Received 22 March 1977; read 2 November 1977; revised typescript received 17 January 1978. HOWARD DAVID JOhnSON, Koninklijke/Shell Exploratie en Produktie Laboratorium, Rijswijk (ZH), The Netherlands. BRUCE KEVIN LEVELL, Dept. of Geology & Mineralogy, Parks Road, Oxford OX1 3PR. STANISLAW SIEDLECKI, Norges Geologiske Undersekelse, P.O. Box 3006, 7001 Trondheim, Norway. Disemsion MR W. B. HARLAr,~ commented on the clear descrip- of breccia and mylonite in so important a transcurrent tion of the Trollfjord-Komagelv fault as an example of fault and he suggested that the fault surface transpression in which strike-slip coupled with com- irregularities might not only be accommodated by sup- pression seemed to have acted together judging by the plementary strike-slip and splay faulting but possibly appearance in cross-sections of steeply dipping strata by squeezing out of material, in reverse dip-slip mo- and minor high angle faults near the major fault. The tion, that would then be lost to view. authors confirmed that the intensity of deformation decreased away from the main fault. Transpressive tectonics should, in theory, be very common, occurring THE Atymoas REPLY" The fault zone was, in fact, at any plate margin oblique to plate motion and yet initially interpreted as a reverse fault system (Sied- the structures were often not so easily interpreted. Mr lecka & Seidlecki 1967) on the basis of the associated Harland was surprised at the relatively small amount steep dips and small-scale reverse faults. Although Downloaded from http://pubs.geoscienceworld.org/jgs/article-pdf/135/5/533/4885633/gsjgs.135.5.0533.pdf by guest on 02 October 2021 534 H. D. Johnson, B. K. Levell & S. Siedlecki there is no evidence of the amount, or even the axes parallel to the fault zone perhaps suggests that direction of any dip-slip movement on the fault, it is the regional transpressive component was minor. entirely probable, to judge from recent strike-slip fault The small amount of fault brec~a and mylonite had systems, that dip-slip did occur. This could have been also surprised the authors, who were grateful for any related to a regional transpression or a local compres- suggestions (such as that of Mr Harland) which might sion across the fault. However the lack of regional fold help clarify the problem. 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