A microseismic monitoring system provides a vital window into a rock mass to see where stress induced fracturing is occurring in relation to mining operations. A main factor for the accuracy of the microseismic locations is the velocity model assumed for the rock mass. The majority of mines that use microseismic systems use a single velocity model for location purposes which assumes the same elastic modulus properties throughout the volume. This study shows examples of event locations that were calculated using a velocity model that accounts for multiple complex shaped geological units each with their own properties. The method allows multiple voids to be added that could be air filled, brine filled, or cement paste back filled, thus mimicking mining and geotechnical operations such as stope mining, cave mining, solution mining, or underground cavern storage. Going beyond the dots, microseismic systems provide an important way to understand the failure mechanics of the rock fracturing. With good data quality, each located event can be solved for the source mechanism (moment tensor) and interpreted in terms of whether the event is dominantly tensile opening, closing, or shear slip. The orientation of each event failed zone can be quantified providing useful information about the discrete fracture network (DFN). This paper provides examples of source mechanism solutions using a full 3D velocity model. It is shown that the ray path of each sensor does affect the source mechanism solution when comparing a single velocity model solution and a 3D velocity model solution. Microseismic systems offer important daily information for mine operation, safety and planning. Improvements to the accuracy of seismic results by using enhanced processing methods and regular calibration, allow a mine to more confidently integrate seismic results with numerical models and make decisions. This is especially important as mines move to different excavation methods such as block caving and extend to greater depths and stresses. Recently, microseismics are playing an essential role in applications such as the monitoring of shale gas hydraulic fracturing and underground storage caverns (Baig et al. 2012). Being able to monitor a 3D volume of rock deep under the ground in real time is very important for tracking any rock fracturing and coalescence that may be occurring. https://papers.acg.uwa.edu.au/p/1410_48_Collins/ 3D velocity model with complex geology and voids for microseismic location and mechanism DS Collins et al.

The National Research Council of Canada has developed a novel ultrasound based Rock Bolt Sensor (RBS™) to monitor load, deformation, and integrity of rock bolts. Several RBSs were deployed to monitor bolts in the roof of an intersection of two drifts and with another region of monitoring tens of metres away in the roof of the drift. The intersection spanned two rock types with different stiffness characteristics. The region was also covered by an extensive seismic system with a mixture of triaxial geophones and both triaxial and uniaxial accelerometers. Using three weeks of recorded data, the loading on 12 bolts was monitored during the production of several nearby stopes and analysed alongside the recorded seismicity. A significant increase in loading on the bolts in the roof was recorded when production occurred within 40 m of the instrumented intersection despite several other stopes producing more significant seismicity following blasting. The load was also taken up asymmetrically, with more substantial changes in load occurring in the bolts in the greywacke. During the study period, several large seismic events occurred within 500 m of the study area. Seismic moment tensor analysis was conducted on several of the seismic events to estimate the mechanism of failure and, using seismic stress inversion, the orientation of the observed fractures was estimated and the directions of principal stress. There was a strong increase in the load on the bolts located in the intersection, across the two different formations, several hours after a large seismic event occurred on that contact several hundred metres away. This work showed a connection between loading on the bolt and large changes in the local stress field due to nearby production and significant seismicity along structures in the region. In addition to monitoring the loading of the rock bolts, the Rock Bolt Sensor can be utilised to better understand the coseismic and post-seismic deformation within the mine and improve models of the local stress field.

The majority of seismic hazard assessment tools are solely based on statistical analyses of several seismic source parameters such as event rate and time, and seismic moment. These analyses are often applied to the entire mining area which can impact the accuracy and reliability of the hazard assessment tool in each zone. Experience has shown that mining geomechanical risk is complex and its mitigation needs a broad understanding of other geotechnical factors such as rock mass properties, geological structures, mining method, stress regime, etc. Since all the contributing parameters and their impact are not entirely understood, it is critical to apply a range of geotechnical/geomechanical analyses in correlation to each other and quantify the changes in the rock mass behaviour. The goal of this paper is to develop a seismic hazard assessment tool calibrated for each geotechnical domain within the mine. To develop the tool, we incorporated mine geotechnical and geological data, seismic source parameters, and tomography analyses from a hard rock underground mine in North America. There exist several sub-vertical faults and one horizontal structure in the mine which create clear contrasts in rock mass behaviour across the structure. The results show good correlation among the different datasets, and a calibrated seismic hazard tool has been developed that provides ongoing updates to the mine operation.

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