Challenges in mine seismology Steve Spottiswoode CSIR

Some challenges facing Mine Seismologists Socio-political environment Economic and cultural globalisation Risk-aversion and safety Who are we? Are we geophysicists or rock engineers? Science (rock strength) Forecasting: long-term Prediction: short-term Seismology and engineering Preconditioning Managing strong ground motion How to use numbers from forecasting and prediction? Near-field vs far-field ground motion Which events are going to be damaging? Mining for less rockburst damage & risk © CSIR 2009 www.csir.co.za

Socio-political environment Are we geophysicists or rock engineers? Economic and cultural globalisation Rock Mechanics conferences, especially Australia, South Africa & Canada Mining companies increasingly source information from around the world. “Just Google it” Boom and bust conditions (sourcing post-grad students) Risk-aversion and safety Investors want to quantify the risks before committing money Financial & safety (will not mine under unsafe conditions) Where, when and how large will the next potentially damaging tremor be? “Seismologist sometimes needs reminding that there is a real world with problems seeking practical engineering solutions. Engineers sometimes need reminding that there is a lot to be learned by properly analysing the problem.” (Wesseloo, 2009) © CSIR 2009 www.csir.co.za

Rock strength Sources at high stress s1 What is the rock strength and how do miners and tunnellers handle failed rock? At a recent conference (SHIRMS) considerable discussion focussed on describing the strength of rock (e.g. Kaiser). The most interesting aspect is in the low-stress region close to mining excavations. Sources at high stress s1 Many modifictions of the Hoek-Brown strength criterion s3 Damage at low stress, often in already damaged rock © CSIR 2009 www.csir.co.za

Can we predict events? Mining seismicity offers many opportunities (challenges) for quantitative models with long-term drivers such as: Stress Stress change or energy “forecasting” Geological discontinuities Aftershocks Can we predict seismic events in the short term? Summary of the state of the art for earthquake prediction was presented by Tom Jordan yesterday As with earthquakes, no, but roof collapses and open-pit failures do seem to be predictable Why? © CSIR 2009 www.csir.co.za

Nature works hard to close up mining voids What controls the amount of seismicity? © CSIR 2009 www.csir.co.za

Stress and stress change Seismicity driven by active mining Seismicity near old mining © CSIR 2009 www.csir.co.za

Mining as a driver of seismicity © CSIR 2009 www.csir.co.za

Drivers of seismicity: geologcal discontinuities © CSIR 2009 www.csir.co.za

Short-term prediction Tom Jordan referred yesterday to the “heroic quest” of searching for the “silver bullet” or intuitive approach to looking for precursors Some mines in SA follow a policy of asessing seismicity on a daily basis to provide estimates of seismic hazard. Hazard changes as mining geometry changes, but does seismicity hold additional information? From aftershocks? Yes From changing patterns of seismicity? Successful predictions of falls of ground? © CSIR 2009 www.csir.co.za

Short-term variations in seismicity by stacking events before & after large events: M>2.5 & 100m in plan Cumulated seismicity, with adjustments for long-term average Running average of properties © CSIR 2009 www.csir.co.za

Radar is being used to predict slope stability Deformation rate Naismith (2005) © CSIR 2009 www.csir.co.za

Predicting falls of ground in a platinum mine with seismicity Cumulated seismicity © CSIR 2009 www.csir.co.za

Seismology and engineering Preconditioning Managing strong ground motion How to use numbers from forecasting and prediction? Near-field vs far-field ground motion Which events are going to be damaging? Mining for less rockburst damage & risk © CSIR 2009 www.csir.co.za

Engineering the rock by preconditioning © CSIR 2009 www.csir.co.za

Engineering: Managing strong ground motion How to use numbers from forecasting and prediction? Must be ~10 times more likely for prediction Near-field vs far-field ground motion Many questions on strong ground motion Which events are going to be damaging? Mining for less rockburst damage & risk Keep people away from possible rockburst damage © CSIR 2009 www.csir.co.za

Conclusions Socio-political environment Science (rock physics) Defined risk and high safety Mines see seismologists as working for rock engineers? Science (rock physics) Forecasting: long-term Prediction: short-term Engineering Preconditioning Managing strong ground motion How to use numbers from forecasting and prediction? Near-field vs far-field ground motion Which events are going to be damaging? Mining for less rockburst damage & risk © CSIR 2009 www.csir.co.za

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