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which occur when high stress concentrations are induced around underground openings (Hoek, 2006) in brittle rock or rock masses with brittle structure. The Canadian Rockburst Handbook (Kaiser, McCreath, and Tannant, 1996) defines a rockburst as: ‘damage to an excavation that occurs in a sudden or violent manner and is associated with a seismic event’. Codelco (2008) uses the following definition of rockburst: ‘Loss of continuity of the production process of the mining operation, caused by the rupture and instant projection of the rock mass, associated with a seismic event.’ It is important to note the evolution, through these three definitions, from a term describing a mechanical phenomenon to a general and then a specific form of damage causing defined consequences. From a hazard and risk management perspective it is important to maintain a separation between the physical process of ‘dynamic rupture’ of the rock around a tunnel (the hazard) and the operational ‘rockburst’ impact (risk). The assessment of the hazard of dynamic rupture is the subject of this paper. In mining, there are many different mechanisms that lead to rockbursts. Pillar failure can be very violent if the pillar core reaches capacity and the mine geometry is such that instantaneous deformations (system unloading) are large. Large stress changes associated with large-scale mining can result in fault slip distant from the drift or shaft but capable of inducing sympathetic strain-bursts (due to stress wave propagation) or seismically induced falls of ground involving previously damaged rock. In tunnelling, however, the most important mechanism, is ‘strain bursting’ (Kaiser, McCreath, and Tannant, 1996) of walls and the tunnel face, with or without structural control and as a result of the complex stress path within the near-field rock as the tunnel advances (Diederichs, Eberhardt, and Fisher, 2013). In this case the stress changes, energy storage, and release mechanisms are often coincident and local to the tunnel boundary. This mechanism is one of dynamic rupture of a competent rock at high induced stress around the tunnel, as shown in Figure 1. The extent and dynamic intensity of the failure can be mitigated by (or enhanced by) structural, compositional, and geometrical components within the rock-tunnel system. The dynamic rupture event can be selftriggered (spontaneous failure of rock with rapid release of stored strain energy), or can be triggered by a seismic strain wave from more distant structures or excavation influence zones. Kaiser, McCreath, and Tannant (1996) classify low-, medium-, and high-level strain bursts (termed here ‘dynamic rupture events’) as involving depths of rupture less than Early assessment of dynamic rupture hazard for rockburst risk management in deep tunnel projects