Authors: Taylor, G; de Wit, T

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Taylor, G & de Wit, T 2023, 'Observing the anatomy of slope failure using time-lapse seismic velocity changes', in PM Dight (ed.), SSIM 2023: Third International Slope Stability in Mining Conference, Australian Centre for Geomechanics, Perth, pp. 733-740,

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The seismic velocity of an Earth material is a key physical characteristic that can provide critical information such as composition, porosity, and overall cohesion of said material. Although such physical properties are typically assumed to be static in time for any given rock mass, it has been observed that the seismic velocity of natural materials can vary with time in response to a variety of processes, which can include environmental, anthropogenic, or tectonic effects. Such processes may include stress-induced slip events or changes in pore fluid pressure. The temporal changes in seismic velocity that result from these effects are typically extremely small (<1%), and are therefore difficult to observe reliably. The best approach to observing temporal seismic velocity variations within a medium does not involve the measurement of travel time delays in direct waves from ballistic seismic events, but instead focuses on multiple scattered waves contained within the ambient seismic noise field. We present a novel experiment in which continuous recordings of ambient seismic noise made within the open pit wall of the Century Mine in Australia are used to track variations in seismic velocity during a period of substantial failure in the stability of the pit wall. We observe a decrease in the bulk seismic velocity of 0.5% during the course of the failure, with the onset of this decrease occurring approximately two weeks prior to the initiation of major surface deformation. The precursory decrease in seismic velocity begins following a nearby mining blast and precedes the onset of other geophysical signals that herald the slope failure, including conventional seismic monitoring, and geodetic observations. We propose that the routine monitoring of seismic velocity variations may be provide critical information, including early warning, in the management of landslide hazards.

Keywords: slope monitoring and its interpretation, slope stability in weak rocks and rock dumps, case studies

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