Our fundamental research focuses on the main differences between processes leading to earthquakes and the seismic rock mass response to mining.
In earthquake seismology the driving forces are fairly constant and relatively slow facilitating the processes of self-organisation. Rock mass subjected to such a process would migrate towards a subcritical state – a state at which the correlation length becomes comparable with the system size and at which the system can develop and maintain reproducible relationships among its distant parts. It is assumed that the growth of long-range correlations within the rock mass allows for progressively larger events to be generated. An important agent in the development of spatial and temporal correlations is seismic activity itself. By breaking numerous asperities, seismic events smooth the system, allowing transfer of stresses over larger distances and thus paving the way for even larger events.
In mines, the rate of the transient convergence associated with rock extraction is at least an order of magnitude greater than that of crustal deformation, which imposes different dynamics on rock mass excitation and on the relaxation processes that follow. If excitation is strong the relaxation process is intermittent with diverging relaxation time and accumulated loading. It is therefore important to appreciate the spatial and temporal extent of these processes.
Mining is not a spontaneous process. It induces stresses at a particular place, at a particular time and at a particular rate, which are all highly variable compared to the tectonic regime This process is controlled more by the commodity prices than by the plate tectonics. This intermittent dynamics influences the development of spatial and temporal correlations and interfering with the act of self-organization. In general mining scenarios that induce spatial and temporal heterogeneity, or disorder, that de-correlate the system are less likely to develop larger dynamic instabilities.
Consequently, unlike earthquakes, the seismic rock mass response to mining can be controlled to a certain degree. The main objective of our fundamental research programme is to understand these control parameters and their limitations.
The main thrust of the applied research is to support the following objectives of seismic monitoring in mines.
- To quantify and to explain the difference between the observed and the expected seismic rock mass response to mining.
- To confirm the rock mass stability related assumptions made during the design process and enable an audit of, and corrections to, the particulars of a given design while mining.
- To quantify and to monitor seismic hazard.
- To detect strong and unexpected changes in seismic rock mass behaviour.
Applied Research also covers our Rock Physics programme, which aims to routinely use other geophysical techniques to monitor the rock mass response to mining. These techniques include the use of controlled, repeatable seismic sources to make routine high-precision measurements of seismic velocities in different zones of the mine. This is known as Active Seismic Monitoring
Applied Research contains another programme called Numerical Stress Modelling, which aims to combine the 3D seismic event data of where the rock is actually failing with the mine geometry and resulting stress fields contained with numerical stress models.
Forensic mine seismology involves a detailed back-analysis of relevant data, in particular seismological records, to confront different plausible scenarios leading to a particular outcome, e.g: increase in seismic activity, rock mass instability and/or damage to the underground or surface structures.
ROUTINE SEISMOLOGICAL SERVICES
Once a new methodology has been developed, it is offered as a cost effective service to the customers. Today we offer the following services.
- Seismological processing of waveforms.
- Seismic system administration.
- Daily/weekly/monthly reporting on seismic activity and associated hazard plus on-line monitoring of particular areas of interest.
- Daily/weekly/monthly numerical modelling of stress and strain changes due to mining for reconciliation with associated seismic activity.
SEISMIC MONITORING TECHNOLOGY
IMS is the leading microseismic monitoring technology provider to mines world wide. We also provide technical services associated with installation, maintenance and 24/7 technical support.