Observation of mining-induced faults in an intact rock mass at depth

摘要

Sloping of a highly-stressed remnant in adeep South African gold mine was accompanied byconsiderable seismic activity and some significantrockbursts. The larger seismic events were registeredsome 60 km away at a World-wide Standard SeismographNetwork (WSSN) station. Several shear ruptures wereencountered subsequently in a tunnel driven to follow the mining faces.A careful study based on detailed exploration of twoof these ruptures proved them to be the source of twoof the larger rockbursts. The ruptures wereessentially planar features of considerable arealextent with shear displacements of up to 100 mm of a normal dip-slip sense.Certain striking features were revealed by a scanningelectron microscopic study of some of the freshcataclastic rock-flour which formed part of thecomminuted filling of these ruptures. These providedstrong evidence for extremely violent fracturingphenomena in the faulting process. A properunderstanding of these phenomena could provide usefulinsight into the source mechanism of rockbursts andthe control of the accompanying damage.Because of the many similarities in morphology of thefaults and in the nature of the seismic signals itcould be argued that the rockburst rupture is amicrocosm of the pristine earthquake. Understandingof the mechanics of the rockburst shear rupture mighttherefore have some relevance in the study of the earthquake source.