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Steve Spottiswoode

University of the Witwatersrand, School of Geosciences, Alumnus

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Short CV – Dr. Stephen Morrison Spottiswoode.
Steve Spottiswoode has worked in the fields of mine seismology rock engineering for 45 years. After completing his PhD work at Wits University, Steve worked at Blyvooruitzicht gold mine for six years where he installed and operated the first mine-wide seismic system wholly owned by a mine in South Africa. In 1986 he joined the Chamber of Mines Research Organisation (COMRO), now CSIR’s Centre for Mining Innovation where he studied seismicity in relation to pillar and mine layout design, strong ground motion and control of rockburst damage.
He has investigated many rockburst sites in order to determine and understand seismic and rockburst mechanisms. He has been involved in the design and implementation of many seismic systems, including the PRISM hardware and AURA software systems. Steve is the author or co-author of over 70 papers in international journals and conferences.
Steve retired from the CSIR in 2009. He is currently working as a private consultant. His current research interests are:
• seismic source mechanisms and layout design of tabular deep-level mines; and
• relative-absolute seismic locations using full waveforms.

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University of KwaZulu-Natal

Friedemann Essrich

The University of Western Australia

Raymond Durrheim

University of the Witwatersrand

Johan WL Hanekom

Gerrie van Aswegen

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Papers by Steve Spottiswoode

Biography Academia edu Steve Spottiswoode

Steve Spottiswoode has worked in the fields of mine seismology rock engineering for 45 years. Aft... more Steve Spottiswoode has worked in the fields of mine seismology rock engineering for 45 years. After completing his PhD work at Wits University, Steve worked at Blyvooruitzicht gold mine for six years where he installed and operated the first mine-wide seismic system wholly owned by a mine in South Africa. In 1986 he joined the Chamber of Mines Research Organisation (COMRO), now CSIR's Centre for Mining Innovation where he studied seismicity in relation to pillar and mine layout design, strong ground motion and control of rockburst damage.

Audit of SIMRAC project GAP 017

The annual reports of 1993 and 1994 and the final project report, marked DRAFT and dated April 19... more The annual reports of 1993 and 1994 and the final project report, marked DRAFT and dated April 1996, were used as a measure of the work done under GAP017. The reports were assessed on their own merit and according to the GAP017 project proposal dated 95/04/28. This reviews contains suggestions for consideration by SIMRAC or the ISS team.

Seismic monitoring of a simulated rockburst on a wall of an underground tunnel

Journal- South African Institute of Mining and Metallurgy

A simulated rockburst was conducted underground at Kopanang Mine, previously called Vaal Reefs No... more A simulated rockburst was conducted underground at Kopanang Mine, previously called Vaal Reefs No. 9 Shaft. The rockburst was simulated by means of a large blast detonated in solid rock close to a crosscut sidewall. The simulated rockburst involved the design of the seismic source, seismic observations in the near and far field, high-speed video filming, a study of rock mass conditions such as fractures, joints, rock strength etc. Knowledge of the site conditions before and after the simulated rockburst was also gained. Some of the important findings are listed below: Two areas of damage were identified on the blasting wall: (i) an area of high-intensity damage in which ground velocities of 3.3 m/s were recorded by an accelerometer, which was subsequently ejected in a block of rock, (ii) an area of low-intensity damage where ground velocities of 1.6 m/s were recorded by an accelerometer which remained on the tunnel wall. High-speed filming revealed rock fragments being ejected from ...

Further assessment of seismic hazard/risk in the Bushveld Complex platinum mines and the implication for regional and local support design

The objective of this project was to assess the seismic risk in the Bushveld Complex platinum min... more The objective of this project was to assess the seismic risk in the Bushveld Complex platinum mines and to provide guidelines for regional and local support in areas where the seismic risk is considered to be high. In order to achieve this objective, seismic data from some recently installed seismic networks were analysed.

Energy and stiffness of mine models and seismicity

Copyright: 2008 Australian Centre for Geomechanics The researchers analysed seismicity in two dee... more Copyright: 2008 Australian Centre for Geomechanics The researchers analysed seismicity in two deep gold mines in terms of strain energy release during mining. Mining took place with regularly-spaced dip pillars and backfill for regional support. The mines were chosen to represent mining of the Carbon Leader reef (CLR) and the Ventersdorp Contact reef (VCR). More than 500,000 m2 of reef were mined over several years and generated more than 10,000 events of magnitude greater than 0,0 in each case. The researchers proposed a simple softening model to explain the CLR behaviour

Meaningful use of peak particle velocities at excavation surfaces for the optimisation of the rockburst criteria for tunnels and stopes

The aim of this project is optimization of rockburst support systems by the systematic evaluation... more

Study of mine stability using records of ground tilting

Tilt data are being used to study the behaviour of deep-level mine layouts, particularly the perf... more Tilt data are being used to study the behaviour of deep-level mine layouts, particularly the performance of dip pillar systems. The tilt data are being recorded by a triggered seismic recording system. The triggered data showed velocity and tilt data that correlated well in time, allowing for separation of the tilt data into coseismic and aseismic tilting. The following results have been obtained from analysis of data recorded over 109 days: Coseismic tilt jumps occur in either direction; the total amount of coseismic tilt in each direction is approximately the same; the time-of-day tilting shows the effect of blasting on the coseismic tilting and, to a lesser degree, on aseismic tilting. As a preliminary interpretation, this can be attributed to the brittle nature of the rock mass and to the “stiff” mining layouts practiced in the area. As a more definitive interpretation, this observation is compatible with a level of stress of the rock blasted at the face that is very much lower ...

Survey and assessment of techniques used to quantify the potential for rock mass instability

The development of techniques to quantify the potential for rockmass instability that may result ... more The development of techniques to quantify the potential for rockmass instability that may result in rockbursts, has been a priority for researchers in the South African gold mining industry for some decades. These techniques include numeric modelling, seismic monitoring, stress and deformation measuring. Industry, COMRO and SIMRAC funding provided for the development of these techniques. The South African research & development efforts towards early warning of large instabilities (rockbursts) are foremost in the world. The question is whether our application in the field of these methodologies, concepts and techniques is equally advanced. During this project the research direction changed slightly to cover a wider perspective of seismic risk assessment. It is therefore relevant at the outset to qualify the term seismic risk as opposed to seismic hazard.

Improvement of worker safety through the investigation of the site response to rockbursts

The objective of this investigation is to improve worker safety through a better understanding of... more The objective of this investigation is to improve worker safety through a better understanding of mine excavation response to rockbursts. The improved understanding should lead to improved mine layout and support design. The project is a continuation of GAP 201 and consists of two main enabling areas namely: a comprehensive investigation of rockbursts that have caused damage and posed a hazard to workers and measurement and analysis of the dynamic response of the rock surrounding excavations following seismic shaking.

A hybrid location methodology

Journal- South African Institute of Mining and Metallurgy

Deterministic properties of mine tremor aftershocks

Mine tremor aftershock sequences from two deep mines in the Far West Rand goldfield, South Africa... more Mine tremor aftershock sequences from two deep mines in the Far West Rand goldfield, South Africa, were analysed in order to determine the influence of geological and mining parameters on the risk posed by aftershocks. Mainshocks were stacked in time and space and the aftershock productivity was calculated for various subsets. Contrary to our working hypothesis, no significant differences were found between the aftershock productivity of mainshocks located in high stress areas and those located in low stress areas, or between mainshocks located in high strain-rate areas and those located in low strain-rate areas, or between mainshocks located near to geological features and those located further away from geological features. Thus, while the incidence of mainshocks may be affected by stress, strain rate and proximity of geological features, these factors do not have significant influence on aftershock productivity. Consequently, guidelines governing the time period and distance from...

A study of mine stability using records of ground tilting

ABSTRACT Tilt data are being used to study the behaviour of deep-level mine layouts, particularly... more ABSTRACT Tilt data are being used to study the behaviour of deep-level mine layouts, particularly the performance of dip pillar systems. The tilt data are being recorded by a triggered seismic recording system. The triggered data showed velocity and tilt data that correlated well in time, allowing for separation of the tilt data into coseismic and aseismic tilting. The following results have been obtained from analysis of data recorded over 109 days: Coseismic tilt jumps occur in either direction; the total amount of coseismic tilt in each direction is approximately the same; the time-of-day tilting shows the effect of blasting on the coseismic tilting and, to a lesser degree, on aseismic tilting. As a preliminary interpretation, this can be attributed to the brittle nature of the rock mass and to the “stiff” mining layouts practiced in the area. As a more definitive interpretation, this observation is compatible with a level of stress of the rock blasted at the face that is very much lower than would have occurred if the rock were infinitely strong and unfractured; and Tilt jumps show a power-law behaviour compatible with the Gutenberg-Richter relationship with b = 1 over more than two orders of magnitude. Numerical tools have been developed to estimate tilting from mining, assuming elastic rock mass behaviour. Some suggestions for further work are made. These include studying changes in a seismic tilting following tilt events associated with shrinking pillars. This might provide more direct insights into pillar stability than are obtained from the general results obtained here.

Improved seismic locations and location techniques

by Steve Spottiswoode, Matthew Handley, and Artur Cichowicz

The location of a seismic event is critically important because not only does a good location pro... more The location of a seismic event is critically important because not only does a good location provide a guide for the rescue effort, but also all other parameters (e.g. moment, and energy) are dependent on it. Location errors scatter the seismic locations, causing them to plot as diffuse clouds, which obscure any seismic patterns that might be emerging. This impacts negatively on seismic hazard assessment, which is often based on spatial-temporal seismicity trends, hence location error has a direct effect on mining safety. There are two broad groups of event location methodologies, namely absolute location methods, and relative location methods. An absolute location is defined in this report as a once-off location of a single seismic event using some or all the seismograms recorded by the seismic system for the event. A relative location uses some or all of the seismograms from two or more neighbouring seismic events to locate them relative to each other. The rationale for relative ...

The use of waveform similarity to define planes of mining-induced seismic events

Tectonophysics, 1998

Mining-induced seismicity results from a complex interaction of ambient and mining-induced stress... more Mining-induced seismicity results from a complex interaction of ambient and mining-induced stresses acting on a rock mass that has been intersected by a variety of geological weaknesses and discontinuities. A major challenge is to improve mine design methodology by identifying the geological features that are seismically active and then changing the direction of mining to reduce the potential for shear

Statistical Properties of Mine Tremor Aftershocks

Pure and Applied Geophysics, 2010

Mine tremors and their aftershocks pose a risk to mine workers in the deep gold mines of South Af... more Mine tremors and their aftershocks pose a risk to mine workers in the deep gold mines of South Africa. The statistical properties of mine-tremor aftershocks were investigated as part of an endeavour to assess the hazard and manage the risk. Data from two gold mines in the Carletonville mining district were used in the analysis. Main shocks were aligned in space and time and the aftershock sequences stacked and analysed. The aftershocks were found to satisfy Gutenberg-Richter scaling, with a b value close to 1. Aftershock activity diminished with time in accordance with the modified Omori law, with p values close to 1. However, the relationship between the main shock and its biggest aftershock violated Båths law, with DM L & 1.9 for main shocks with M L \ 3 and increasing for main shocks with M L [ 3. The aftershock density was found to fall-off with distance as r -1.3 , suggesting triggering by dynamic stress.

Exploring the possibility of mining the stabilising pillars in South African gold mines

Effect of the Rock Properties on Mining-induced Seismicity Around the Ventersdorp Contact Reef, Witwatersrand Basin, South Africa

Ð The Ventersdorp Contact Reef is characterised by a variety of dierent rock types that are found... more Ð The Ventersdorp Contact Reef is characterised by a variety of dierent rock types that are found above and below the reef in dierent mining areas. These variations in the host rock type have been classi®ed into six main geotechnical areas. Knowledge of the dierence in seismicity related to these geotechnical areas could in¯uence the design of deep level stopes and optimise the support systems.

Integrated seismicity around deep-level stopes in South Africa

International Journal of Rock Mechanics and Mining Sciences, 1997

Stresses acting on a rock mass, elastic deformations of the area mined out, the amount and method... more Stresses acting on a rock mass, elastic deformations of the area mined out, the amount and method of mining, geological features and rock properties are known to influence mining induced seismicity. The effect of stress and mining method on seismicity can be measured by the ratio (TE) of cumulative seismic moment to the product of rigidity and volume of elastic convergence. The seismic moment has a logarithmic nature and can be dominated by the few largest events. To reduce this effect we use a supplementary parameter that is empirically related to the incidence of rockburst fatalities (TR). As larger events are less hazardous per unit of seismic moment, 7R is less controlled by the largest seismic events.

Coseismic and other short-term strain changes recorded with Sacks-Evertson strainmeters in a deep mine, South Africa

by Steve Spottiswoode and Arthur McGarr

Geophysical Journal of the Royal Astronomical Society, 1982

Sacks-Evertson borehole dilatometers were installed at the ends of boreholes drilled into the sid... more Sacks-Evertson borehole dilatometers were installed at the ends of boreholes drilled into the sidewall of an experimental tunnel at a depth of 3.1 km in the ERPM gold mine near Johannesburg. In the following year coseismic strain changes ranging from 5 x lo-'' to values exceeding 5 x lo-(' were recorded for hundreds of mine tremors in the magnitude range -1 to 3.7 and at hypocentral distances of 5 0 m to about 2 km. Hypocentral coordinates and magnitudes were determined from seismograms recorded from an underground array of geophones. Amplitudes and polarities of the coseismic strain steps are generally in excellent agreement with theoretical expectations based on point-source dislocation theory; specifically, the strain steps are proportional to the seismic moment divided by the cube of hypocentral distance. At a strain level of 5 x lod9 or greater the tremors do not appear to be preceded by any short-term indications of instability even for tremors producing coseismic steps greater than 5 x and for which the strainmeters were within a source radius of the hypocentre. Continuous strain changes observed at the times when the mine excavation, at a distance of about 100 m, is extended are in good agreement with calculated changes based on the theory of elasticity. A similar calculation is consistent with post-seismic strain changes observed to follow some of the closer tremors. These post-seismic strains show a logarithmic dependence on time following the tremor and appear to be due to the interaction of a tremor with the adjacent mine excavation rather than to deformation within the actual seismic source region. Date Time bl 05 J u l y 77 1646 1.2 x lo-' 06 J u l y 07 J u l y OM J u l y 09 J u l y 12 J u l y 14 J u l y 16 J u l y

Volume excess shear stress and cumulative seismic moments

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1991

Biography Academia edu Steve Spottiswoode

Steve Spottiswoode has worked in the fields of mine seismology rock engineering for 45 years. Aft... more Steve Spottiswoode has worked in the fields of mine seismology rock engineering for 45 years. After completing his PhD work at Wits University, Steve worked at Blyvooruitzicht gold mine for six years where he installed and operated the first mine-wide seismic system wholly owned by a mine in South Africa. In 1986 he joined the Chamber of Mines Research Organisation (COMRO), now CSIR's Centre for Mining Innovation where he studied seismicity in relation to pillar and mine layout design, strong ground motion and control of rockburst damage.

Audit of SIMRAC project GAP 017

The annual reports of 1993 and 1994 and the final project report, marked DRAFT and dated April 19... more The annual reports of 1993 and 1994 and the final project report, marked DRAFT and dated April 1996, were used as a measure of the work done under GAP017. The reports were assessed on their own merit and according to the GAP017 project proposal dated 95/04/28. This reviews contains suggestions for consideration by SIMRAC or the ISS team.

Seismic monitoring of a simulated rockburst on a wall of an underground tunnel

Journal- South African Institute of Mining and Metallurgy

A simulated rockburst was conducted underground at Kopanang Mine, previously called Vaal Reefs No... more A simulated rockburst was conducted underground at Kopanang Mine, previously called Vaal Reefs No. 9 Shaft. The rockburst was simulated by means of a large blast detonated in solid rock close to a crosscut sidewall. The simulated rockburst involved the design of the seismic source, seismic observations in the near and far field, high-speed video filming, a study of rock mass conditions such as fractures, joints, rock strength etc. Knowledge of the site conditions before and after the simulated rockburst was also gained. Some of the important findings are listed below: Two areas of damage were identified on the blasting wall: (i) an area of high-intensity damage in which ground velocities of 3.3 m/s were recorded by an accelerometer, which was subsequently ejected in a block of rock, (ii) an area of low-intensity damage where ground velocities of 1.6 m/s were recorded by an accelerometer which remained on the tunnel wall. High-speed filming revealed rock fragments being ejected from ...

Further assessment of seismic hazard/risk in the Bushveld Complex platinum mines and the implication for regional and local support design

The objective of this project was to assess the seismic risk in the Bushveld Complex platinum min... more The objective of this project was to assess the seismic risk in the Bushveld Complex platinum mines and to provide guidelines for regional and local support in areas where the seismic risk is considered to be high. In order to achieve this objective, seismic data from some recently installed seismic networks were analysed.

Energy and stiffness of mine models and seismicity

Copyright: 2008 Australian Centre for Geomechanics The researchers analysed seismicity in two dee... more Copyright: 2008 Australian Centre for Geomechanics The researchers analysed seismicity in two deep gold mines in terms of strain energy release during mining. Mining took place with regularly-spaced dip pillars and backfill for regional support. The mines were chosen to represent mining of the Carbon Leader reef (CLR) and the Ventersdorp Contact reef (VCR). More than 500,000 m2 of reef were mined over several years and generated more than 10,000 events of magnitude greater than 0,0 in each case. The researchers proposed a simple softening model to explain the CLR behaviour

Meaningful use of peak particle velocities at excavation surfaces for the optimisation of the rockburst criteria for tunnels and stopes

The aim of this project is optimization of rockburst support systems by the systematic evaluation... more

Study of mine stability using records of ground tilting

Tilt data are being used to study the behaviour of deep-level mine layouts, particularly the perf... more Tilt data are being used to study the behaviour of deep-level mine layouts, particularly the performance of dip pillar systems. The tilt data are being recorded by a triggered seismic recording system. The triggered data showed velocity and tilt data that correlated well in time, allowing for separation of the tilt data into coseismic and aseismic tilting. The following results have been obtained from analysis of data recorded over 109 days: Coseismic tilt jumps occur in either direction; the total amount of coseismic tilt in each direction is approximately the same; the time-of-day tilting shows the effect of blasting on the coseismic tilting and, to a lesser degree, on aseismic tilting. As a preliminary interpretation, this can be attributed to the brittle nature of the rock mass and to the “stiff” mining layouts practiced in the area. As a more definitive interpretation, this observation is compatible with a level of stress of the rock blasted at the face that is very much lower ...

Survey and assessment of techniques used to quantify the potential for rock mass instability

The development of techniques to quantify the potential for rockmass instability that may result ... more The development of techniques to quantify the potential for rockmass instability that may result in rockbursts, has been a priority for researchers in the South African gold mining industry for some decades. These techniques include numeric modelling, seismic monitoring, stress and deformation measuring. Industry, COMRO and SIMRAC funding provided for the development of these techniques. The South African research & development efforts towards early warning of large instabilities (rockbursts) are foremost in the world. The question is whether our application in the field of these methodologies, concepts and techniques is equally advanced. During this project the research direction changed slightly to cover a wider perspective of seismic risk assessment. It is therefore relevant at the outset to qualify the term seismic risk as opposed to seismic hazard.

Improvement of worker safety through the investigation of the site response to rockbursts

The objective of this investigation is to improve worker safety through a better understanding of... more The objective of this investigation is to improve worker safety through a better understanding of mine excavation response to rockbursts. The improved understanding should lead to improved mine layout and support design. The project is a continuation of GAP 201 and consists of two main enabling areas namely: a comprehensive investigation of rockbursts that have caused damage and posed a hazard to workers and measurement and analysis of the dynamic response of the rock surrounding excavations following seismic shaking.

A hybrid location methodology

Journal- South African Institute of Mining and Metallurgy

Deterministic properties of mine tremor aftershocks

Mine tremor aftershock sequences from two deep mines in the Far West Rand goldfield, South Africa... more Mine tremor aftershock sequences from two deep mines in the Far West Rand goldfield, South Africa, were analysed in order to determine the influence of geological and mining parameters on the risk posed by aftershocks. Mainshocks were stacked in time and space and the aftershock productivity was calculated for various subsets. Contrary to our working hypothesis, no significant differences were found between the aftershock productivity of mainshocks located in high stress areas and those located in low stress areas, or between mainshocks located in high strain-rate areas and those located in low strain-rate areas, or between mainshocks located near to geological features and those located further away from geological features. Thus, while the incidence of mainshocks may be affected by stress, strain rate and proximity of geological features, these factors do not have significant influence on aftershock productivity. Consequently, guidelines governing the time period and distance from...

A study of mine stability using records of ground tilting

ABSTRACT Tilt data are being used to study the behaviour of deep-level mine layouts, particularly... more ABSTRACT Tilt data are being used to study the behaviour of deep-level mine layouts, particularly the performance of dip pillar systems. The tilt data are being recorded by a triggered seismic recording system. The triggered data showed velocity and tilt data that correlated well in time, allowing for separation of the tilt data into coseismic and aseismic tilting. The following results have been obtained from analysis of data recorded over 109 days: Coseismic tilt jumps occur in either direction; the total amount of coseismic tilt in each direction is approximately the same; the time-of-day tilting shows the effect of blasting on the coseismic tilting and, to a lesser degree, on aseismic tilting. As a preliminary interpretation, this can be attributed to the brittle nature of the rock mass and to the “stiff” mining layouts practiced in the area. As a more definitive interpretation, this observation is compatible with a level of stress of the rock blasted at the face that is very much lower than would have occurred if the rock were infinitely strong and unfractured; and Tilt jumps show a power-law behaviour compatible with the Gutenberg-Richter relationship with b = 1 over more than two orders of magnitude. Numerical tools have been developed to estimate tilting from mining, assuming elastic rock mass behaviour. Some suggestions for further work are made. These include studying changes in a seismic tilting following tilt events associated with shrinking pillars. This might provide more direct insights into pillar stability than are obtained from the general results obtained here.

Improved seismic locations and location techniques

by Steve Spottiswoode, Matthew Handley, and Artur Cichowicz

The location of a seismic event is critically important because not only does a good location pro... more The location of a seismic event is critically important because not only does a good location provide a guide for the rescue effort, but also all other parameters (e.g. moment, and energy) are dependent on it. Location errors scatter the seismic locations, causing them to plot as diffuse clouds, which obscure any seismic patterns that might be emerging. This impacts negatively on seismic hazard assessment, which is often based on spatial-temporal seismicity trends, hence location error has a direct effect on mining safety. There are two broad groups of event location methodologies, namely absolute location methods, and relative location methods. An absolute location is defined in this report as a once-off location of a single seismic event using some or all the seismograms recorded by the seismic system for the event. A relative location uses some or all of the seismograms from two or more neighbouring seismic events to locate them relative to each other. The rationale for relative ...

The use of waveform similarity to define planes of mining-induced seismic events

Tectonophysics, 1998

Mining-induced seismicity results from a complex interaction of ambient and mining-induced stress... more Mining-induced seismicity results from a complex interaction of ambient and mining-induced stresses acting on a rock mass that has been intersected by a variety of geological weaknesses and discontinuities. A major challenge is to improve mine design methodology by identifying the geological features that are seismically active and then changing the direction of mining to reduce the potential for shear

Statistical Properties of Mine Tremor Aftershocks

Pure and Applied Geophysics, 2010

Mine tremors and their aftershocks pose a risk to mine workers in the deep gold mines of South Af... more Mine tremors and their aftershocks pose a risk to mine workers in the deep gold mines of South Africa. The statistical properties of mine-tremor aftershocks were investigated as part of an endeavour to assess the hazard and manage the risk. Data from two gold mines in the Carletonville mining district were used in the analysis. Main shocks were aligned in space and time and the aftershock sequences stacked and analysed. The aftershocks were found to satisfy Gutenberg-Richter scaling, with a b value close to 1. Aftershock activity diminished with time in accordance with the modified Omori law, with p values close to 1. However, the relationship between the main shock and its biggest aftershock violated Båths law, with DM L & 1.9 for main shocks with M L \ 3 and increasing for main shocks with M L [ 3. The aftershock density was found to fall-off with distance as r -1.3 , suggesting triggering by dynamic stress.

Exploring the possibility of mining the stabilising pillars in South African gold mines

Effect of the Rock Properties on Mining-induced Seismicity Around the Ventersdorp Contact Reef, Witwatersrand Basin, South Africa

Ð The Ventersdorp Contact Reef is characterised by a variety of dierent rock types that are found... more Ð The Ventersdorp Contact Reef is characterised by a variety of dierent rock types that are found above and below the reef in dierent mining areas. These variations in the host rock type have been classi®ed into six main geotechnical areas. Knowledge of the dierence in seismicity related to these geotechnical areas could in¯uence the design of deep level stopes and optimise the support systems.

Integrated seismicity around deep-level stopes in South Africa

International Journal of Rock Mechanics and Mining Sciences, 1997

Stresses acting on a rock mass, elastic deformations of the area mined out, the amount and method... more Stresses acting on a rock mass, elastic deformations of the area mined out, the amount and method of mining, geological features and rock properties are known to influence mining induced seismicity. The effect of stress and mining method on seismicity can be measured by the ratio (TE) of cumulative seismic moment to the product of rigidity and volume of elastic convergence. The seismic moment has a logarithmic nature and can be dominated by the few largest events. To reduce this effect we use a supplementary parameter that is empirically related to the incidence of rockburst fatalities (TR). As larger events are less hazardous per unit of seismic moment, 7R is less controlled by the largest seismic events.

Coseismic and other short-term strain changes recorded with Sacks-Evertson strainmeters in a deep mine, South Africa

by Steve Spottiswoode and Arthur McGarr

Geophysical Journal of the Royal Astronomical Society, 1982

Sacks-Evertson borehole dilatometers were installed at the ends of boreholes drilled into the sid... more Sacks-Evertson borehole dilatometers were installed at the ends of boreholes drilled into the sidewall of an experimental tunnel at a depth of 3.1 km in the ERPM gold mine near Johannesburg. In the following year coseismic strain changes ranging from 5 x lo-'' to values exceeding 5 x lo-(' were recorded for hundreds of mine tremors in the magnitude range -1 to 3.7 and at hypocentral distances of 5 0 m to about 2 km. Hypocentral coordinates and magnitudes were determined from seismograms recorded from an underground array of geophones. Amplitudes and polarities of the coseismic strain steps are generally in excellent agreement with theoretical expectations based on point-source dislocation theory; specifically, the strain steps are proportional to the seismic moment divided by the cube of hypocentral distance. At a strain level of 5 x lod9 or greater the tremors do not appear to be preceded by any short-term indications of instability even for tremors producing coseismic steps greater than 5 x and for which the strainmeters were within a source radius of the hypocentre. Continuous strain changes observed at the times when the mine excavation, at a distance of about 100 m, is extended are in good agreement with calculated changes based on the theory of elasticity. A similar calculation is consistent with post-seismic strain changes observed to follow some of the closer tremors. These post-seismic strains show a logarithmic dependence on time following the tremor and appear to be due to the interaction of a tremor with the adjacent mine excavation rather than to deformation within the actual seismic source region. Date Time bl 05 J u l y 77 1646 1.2 x lo-' 06 J u l y 07 J u l y OM J u l y 09 J u l y 12 J u l y 14 J u l y 16 J u l y

Volume excess shear stress and cumulative seismic moments

International Journal of Rock Mechanics and Mining Sciences & Geomechanics Abstracts, 1991