New life breathed into research

Mine seismology research is in need of resuscitation. Aleksander J. Mendecki, Chairman of the Institute of Mine Seismology explains how the institute, formed last year in South Africa and Australia, plans to nurse it back to health.

The progress in mine seismology research over the past ten years has been slow. Practically all the methodologies applied today are based on research done in earthquake seismology in 70s and in mine seismology in 90s.

The intellectual capacity to conduct research at the theoretical level has sadly dwindled and applied research is frequently a simple reapplication of work done in earthquake seismology using data from mine networks.

The Institute of Mine Seismology (IMS) was incorporated in March 2010 in both South Africa and Australia. Its main objective is to invigorate scientific research into seismic rock mass response to mining.

In October 2010 the institute agreed to acquire the entire shareholding of ISS International Limited and of ISS Pacific. Since then, the institute has been widely owned by its professional staff.

As of September 2011, the IMS employs 50 people, including 20 seismologists. In addition there are 24 associated trained seismological processors in South Africa and eight in China processing over 130 000 seismograms from 150 mines each day.

The IMS currently supports over 170 customers in 30 countries. There are over 50 active IMS seismic monitoring systems in South Africa, 50 in Australia and over 70 in the rest of the world. The institute is the largest mine seismology research and development organisation in the world.

The mine seismology research programme of the IMS is co-ordinated by its International Research Advisory Board. This board consists of the industry patrons of the institute, its research fellows and an independent chairman. Professor Peter Kaiser is the current chairman and the research programme is supported by Anglo American Platinum, AngloGold-Ashanti, Nickel West (BHP Billiton), El Teniente (Codelco), Goldfields, Harmony, LKAB and Newcrest.

[GRAPH 1] Intensity of ground motion around finite source propagating in a foot-wall towards the tabular stope (left), and synthetic seismograms calculated at a particular point (right).

Research projects

The 2011/12 IMS research programme supports the following projects:

1. Seismic source modelling - to obtain higher order source parameters, such the direction of rupture propagation, rise time and slip velocity. Obtaining these parameters would help to eliminate some of the ambiguities from first order source mechanism approximations and thus aid the comparison of local geology with seismogram data to better understand what happened to cause a large seismic event.
2. Modelling strong ground motion - to model strong ground motions produced by large complex events at strategic locations in mine and at the surface, as shown in Graph 1. A more accurate tool such as this would make it possible to plan new mine levels and infrastructure in such a way as to minimise the risk of seismic damage.
3. Inversion of active and passive seismic data recorded in mines - to improve the accuracy of 3D seismic velocity inversion enough so that it can be used as a routine tool to better monitor the rock mass response to mining.
4. Integration of numerical and observed mechanisms of seismic sources - to model source mechanisms of seismic events in mines, including larger complex ones with many zones of inelastic deformation that interact with or even intersect excavations and are accompanied by a local volume change. It should constrain numerical models using source mechanisms of observed seismic events and facilitate interpretation.
5. Field trials of embedded pre-stacking - to subject new time synchronisation methods and hardware as well as embedded pre-sta king algorithms to field trials to facilitate mine-scale active seismic monitoring.
6. Cave front tracking - to develop a tool for better estimation of the cave progress through high accuracy measurements of seismic velocity around the cave.
7. Automatic processing of waveforms - to develop and test automatic picking and processing algorithms for mine seismogram data, and thus reduce the reliance on manual processing before any accurate analysis is possible. This would increase the consistency and reliability of seismogram processing, as this repetitive task is sometimes subject to human error despite quality control procedures and checks.
8. Short-term seismic hazard rating - to develop an improved and objective short-term hazard rating tool capable of running online with minimal human intervention. This would help to enable continuous 24/7 rating of seismic hazard for different working places in the mine, improving miner safety.
9. Face burst hazard at West-Wits VCR - to establish seismicity patterns indicative of increased face burst hazard. If successful, potentially hazardous conditions would be better identified and thus avoided.

The institute will continue to organise the yearly seminars on monitoring and modelling seismic rock mass response to mining.

Get your diaries out, because the 22nd such seminar will start on Monday, 7 May 2012, at Assara Estate in Stellenbosch. As usual, the programme will include two days of lectures and presentations followed by three days of training courses covering different aspects of managing seismic hazard in mines.

There will also be one-day IMS seminar at the Sheraton Hotel in Perth on 27 March 2012, preceding the deep mine conference organised by the Australian Centre for Geomechanics (ACG).