Did they blow it? Time-lapse velocity variations during an open-pit mine slope failure using seismic noise interferometry

Landslides are geological events that directly impact thousands of people every year and cause significant loss of life. Landslides are often triggered by extreme weather events or earthquakes. While most slope monitoring approaches focus on surface deformation (e.g. using radar), in some cases by the time changes manifest at surface, it can be too late to provide adequate early warning. Seismic ambient noise correlation has been successfully applied in landslide monitoring, but has yet to be applied on the slope of an open-pit mine. This approach measures time-lapse seismic velocity changes in the subsurface of a slope. Several cases of precursory changes have been shown using seismic ambient noise correlation and shows promise in providing early warning of failure. We present a case study from a dense borehole geophone array installed beneath a well-instrumented slope of an open-pit mine in Australia. We applied seismic ambient noise correlation across a period of slope failure and measured a decrease in seismic velocity approximately 12 days prior to the initiation of the slope failure. We investigated this change and its relationship to seismicity, rainfall and surface deformation recorded during this period.