Table Of ContentSeismic Monitoring in Mines
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Seismic
Monitoring
in Mines
Edited by
Dr A.J. Mendecki
Managing Director and Head of Research at ISS International,
Welkom, South Africa
CHAPMAN & HALL
London· Weinheim . New York· Tokyo· Melbourne· Madras
Published by Chapman & Hall, 2-6 Bouudary Row, Loudon SEI SHN, UK
Chapman & Hall, 2-6 Boundary Row, London SEI 8HN, UK
Chapman & Hall GmbH, Pappelallee 3, 69469 Weinheim, Germany
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Chapman & Hall Australia, 102 Dodds Street, South Melbourne,
Victoria 3205, Australia
Chapman & Hall India, R. Seshadri, 32 Second Main Road, CIT East,
Madras 600 035, India
First edition 1997
© 1997 Chapman & Hall
Softcover reprint ofthe hardcover I st edition 1997
Production control and typesetting by Anne Hordley
ISBN-13: 978-94-010-7187-1 e-ISBN-13: 978-94-009-1539-8
001: 10.1 007/978-94-009-1539-8
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Contents
List of contributors ix
Preface xi
Acknow ledgements Xlll
1. Seismic transducers 1
P Mountfort; A J Mendecki
1.1 Requirements imposed by ground motion 1
1.2 Theory of inertial sensor operation 6
1.3 Realizable sensor characteristics 10
1.3.1 Geophones 11
1.3.2 Accelerometers 13
1.4 Network considerations 16
1.4.1 Results of sensor evaluation field trials 17
1.5 Sensor orientation 19
2. Seismic monitoring systems 21
P Mountfort; A J Mendecki
2.1 Signal conditioning 23
2.1.1 Calibration signal injection 23
2.1.2 Anti-aliasing filters 24
2.1.3 Reduction in dynamic range 27
2.1.4 Analogue to digital conversion 28
2.1.5 Data transmission 29
2.2 Triggering and validation 31
2.2.1 Event detection 31
2.2.2 Pre-trigger data and end of event 33
2.2.3 Validation 33
2.3 Digital data communications 33
2.3.1 Maximising the information rate 34
2.3.2 Low level protocols 35
2.4 Association 36
2.5 Central processing site 39
2.6 System Performance 39
vi Contents
3. Deconvolution, polarization and 41
wavelet transform of seismic signals
A H DzhaJarov
3.1 Deconvolution 41
3.1.1 Deconvolution filters for seismic systems 41
3.1.2 Inverse digital filters for second order
Butterworth high cut filters 42
3.1.3 Inverse digital filters of integrators and
differentiators 44
3.1.4 An iterative technique for the
deconvolution of seismograms 48
3.2 Polarisation 49
3.2.1 Three axis principal components method 49
3.2.2 Complex polarization filters 53
3.3 Wavelet transform 57
4. Seismic rayt racing 67
A H DzhaJarov
4.1 Shooting and bending 68
4.2 Point-to-curve 69
4.3 Finite difference 73
4.4 Wavefront construction methods 82
5. Location of seismic events 87
A J Mendecki; M Sciocatti
5.1 Location by arrival times and/or
directions or azimuths 87
5.2 Relative location and similarity of waveforms 94
5.3 Joint hypocentre and velocity determination
for clusters of events 97
5.4 Optimal spatial distribution of seismic stations 100
5.4.1 Optimality with respect to location error -
a statistical approach 101
5.4.2 Optimality with respect to location error -
a direct approach 103
5.4.3 Example of planning the spatial configuration
of seismic stations 106
Contents vii
6. Seismic velocity inversion from microseismic data 108
S C Maxwell; R P Young
6.1 Seismic tomography 108
6.2 Arrival-time inversion 110
6.3 Application 113
6.4 Velocity inversion in a combined seismological 117
and geomechanical investigation
7. Seismic source radiation and 119
moment tensor in the time domain
J Niewiadomski
7.1 Radiation from the seismic source -
far, intermediate and near fields 119
7.2 Moment tensor 135
7.2.1 The case of a sysnchronous source and
the delta source time function 137
7.2.2 The case of an asynchronous source and
arbitrary source time function 137
8. Spectral analysis and seismic source parameters 144
A J Mendecki; J Niewiadomski
8.1 Fast Fourier transform and multitaper 144
8.2 Source parameters from spectra 152
9. Nonlinear dynamics of seismic flow of rock 159
S Radu; M Sciocatti; A J Mendecki
9.1 Phase space 160
9.2 Reconstruction of the phase space
from seismic data 164
9.3 Fractal correlation dimension 167
9.4 Numerical results 169
9.5 Lyapunov exponent and limits of predictability 173
viii Contents
10. Quantitative seismology and rockmass stability 178
A J Mendecki
10.1 Quantitative description of a seismic event 178
10.1.1 Seismic moment, source size and stress drop 179
10.1.2 Seismic energy 184
10.1.3 Apparent stress, energy index and
apparent volume 185
10.2 Quantitative description of seismicity 193
10.2.1 Seismic strain and seismic stress 195
10.2.2 Unstable system and seismic softening 198
10.2.3 Seismic viscosity, relaxation time and
seismic Deborah number 208
10.2.4 Seismic dissipation and seismic diffusion 210
10.2.5 Seismic Schmidt number 213
10.3 Nucleation of instability and time to failure 213
11. Application of quantitative seismology in mines 220
G van Aswegen; A J Mendecki; C Funk
11.1 Introduction 220
11.2 Benchmark case studies 222
11.2.1 Brunswick Mining and Smelting 222
11.2.2 Tanton fault 223
11.2.3 Western Holdings No.6 shaft pillar 226
11.2.4 Postma dyke 232
11.2.5 The Trough event 239
11.2.6 811122 Longwall 241
References 246
Index 259
Contributors
Dr A.H. Dzhafarov
ISS International, South Africa
Mr C. Funk
ISS International, South Africa
Dr S.c. Maxwell
Department of Geophysics, Keele University, UK
Dr A.J. Mendecki
ISS International, South Africa
Dr P. Mountfort
ISS International, South Africa
Dr J. Niewiadomski
ISS International, South Africa
Dr S. Radu
ISS International, South Africa
Mr M. Sciocatti
ISS International, South Africa
Dr G. van Aswegen
ISS International, South Africa
Prof R.P. Young
Department of Geophysics, Keele University, UK
Preface
Routine seismic monitoring in mines was introduced over 30 years ago with
two main objectives in mind:
• immediate location of larger seIsmIC events to guide rescue
operations;
• prediction of large rockmass instabilities.
The first objective was achieved fairly quickly, but with the subsequent
development of mine communication systems, its strategic importance has
diminished. The very limited success with prediction can, at least partially,
be attributed to three factors:
• seismic monitoring systems based on analogue technology that
provided noisy and, frequently, poorly calibrated data of limited
dynamic range;
• the non-quantitative description of a seismic event by at best its local
magnitude; and
• the resultant non-quantitative analysis of seismicity, frequently
through parameters of some statistical distributions, with a somewhat
loose but imaginative physical interpretation.
The introduction of modern digital seismic systems to mines and progress
in the theory and methods of quantitative seismology have enabled the
implementation of realtime seismic monitoring as a management tool,
quantifying rockmass response to mining and achieving the first tangible
results with prediction.
A seismic event, being a sudden inelastic deformation within the rockmass,
can now routinely be quantified in terms of seismic moment, its tensor, and
radiated seismic energy, so that the overall size of, and stress released at, the
seismic source can be estimated.
Thus seismicity, being the intermittent momentum flux due to the sudden
motion of discrete lumps of rock, and its associated stress and strain changes
in the rock, can be quantified. This brings seismology into the realms of rock
mechanics and rheology, where changes in stress, strain rate, flow viscosity
and diffusion are fundamental in determining the stability of the deforming
