Ortlepp Shears — Dynamic Brittle Shears of South African Gold Mines

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.