Ortlepp Shears — Dynamic Brittle Shears of South African Gold Mines

Authors: van Aswegen, G

DOI https://doi.org/10.36487/ACG_repo/808_160

Cite As:
van Aswegen, G 2008, 'Ortlepp Shears — Dynamic Brittle Shears of South African Gold Mines', in Y Potvin, J Carter, A Dyskin & R Jeffrey (eds), SHIRMS 2008: Proceedings of the First Southern Hemisphere International Rock Mechanics Symposium, Australian Centre for Geomechanics, Perth, pp. 111-119, https://doi.org/10.36487/ACG_repo/808_160

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Abstract:
For many, Mr David Ortlepp will be best remembered for his detailed descriptions of the dynamic brittle shears, being the sources of some typical rockbursts in South African mines. In this paper the distinguishing features of these shears are reviewed and it is argued that they are sufficiently unique to warrant a special name – Ortlepp shears. Three examples are used to explain characteristic features of these shear zones, introducing the terms ‘overshoot’, ‘shear zone wall lineations’ and ‘breakthrough shear ruptures’ as part of the terminology describing the phenomenon. The once-off dynamic origin in strong, siliceous quartzites explains the lack of the classic shear zone fabrics described by Tchalenko (1970) and others.

References:
Bosman, J.D. and van Aswegen, G. (2003) Dynamic failure of pillar remnants – case studies, ISRM 2003–Technology roadmap for rock mechanics, SAIMM, Johannesburg, pp. 143–149.
Brummer, R.K. (1987) Fracturing and deformation at edges of tabular excavations: development of a numerical model describing such phenomena, Unpub. PhD thesis, Rand Afrikaans University, p. 204.
Gay, N.C. and Ortlepp, W.D. (1978) The anatomy of a mining induced fault zone, Geol. Soc. Am. Bull., Part 1, 90, pp. 47–58.
Jager, A.J. and Ryder, J.A. (1999) A handbook on rock engineering practice for tabular hard rock mines, SIMRAC, Johannesburg, p. 371.
Lockner, D.A., Byerlee, J.D., Kuksenko, V., Ponomarev, A. and Sidorin, A. (1992) Observations of quasi-static fault growth from acoustic emissions, In: Fault Mechanics and Transport Properties of Rocks, Evans, B. and Wong, T-F. (editors), Academic Press, San Diego, pp. 3–31.
Logan, J.M., Friedman, M., Higgs, N., Dengo, C. and Shimamoto, T. (1979) Experimental studies of simulated fault gouge and their application to studies of natural fault zones, Proc. Conf. VIII, Analysis of Actual Fault Zones in Bedrock, U.S. Geol. Surv., Open-File Rept., 79–1239, pp. 305–343.
McGarr, A. (1971) Violent deformation of rock near deep level, tabular excavations – seismic events, Bull. Seismological Soc. Amer., 61, No. 5, pp. 1453–1466.
McGarr, A., Pollard, D., Gay, N.C. and Ortlepp, W.D. (1979) Observations and analysis of structures in exhumed mine-induced faults, U.S. Geological Survey Open File Report., 79–1239, pp. 101–120.
McGarr, A., Spottiswoode, S.M. and Gay, N.C. (1979) Observations relevant to seismic driving stress, stress drop and efficiency, J. Geoph. Res., 84, B3, pp. 2251–2261.
Ortlepp, W.D. (1997) Rock Fracture and Rockbursts – An Illustrative Study, SAIMM, Johannesburg, p. 98.
Ortlepp, W.D. (2000) A Study of Rockburst Source Mechanism, Final Project Report, GAP 524, SIMRAC, Johannesburg.
Reches, Z. and Dewers, T.A. (2005) Gouge Formation by Dynamic Pulverization During Earthquake Rupture, Earth and Planetary Science Letters, 235, pp. 361–374.
Sibson, R.H. (1986) Brecciation processes in fault zones: inferences from earthquake rupturing, Pure Appl. Geophys., 124, pp. 159–175.
Tchalenko, J.S. (1970) Similarities between shear zones of different magnitudes, Geol. Soc. Amer. Bull., 81, pp. 41–60.
van Aswegen, G. (in prep) Observational and seismological aspect of an extreme rockburst, RaSiM7.
Wibberley, C.A.J., Petit, J.-P. and Rives, T. (2000) Micromechanics of shear rupture and the control of normal stress, J. Struct. Geol., 22, pp. 411–427.
Wilson, B., Dewers, T.A., Reches, Z. and Brune, J. (2005) Particle size and energetics of gouge from earthquake rupture zones, Nature 434, pp. 749–752.




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