1. By Alex Milev, Steve Spottiswoode and Thabang Kgarume
Coseismic and Aseismic Deformations of the Rock Mass Around Deep Level Mining By
Alex Milev, Steve Spottiswoode and Thabang Kgarume

2. Coseismic and Aseismic Deformations of the Rock Mass Around Deep Level Mining
Definition of quasi-static and dynamic deformations
Integrated monitoring systems
Underground sites
Data analysis
Case study of M 2.1 seismic event at Mponeng mine
Coseismic and aseismic deformations related to mining
Conclusions

3. South Rand VAAL RIVER WEST WITS Moab Khotsong Mponeng Tau Lekoa /
Johannesburg
VAAL RIVER
WEST WITS
Moab
Khotsong
Mponeng
Tau
Lekoa /
Goedgenoeg
Tona Ko
panang
Great N
oligwa
Weltevreden
Kloof
Ergo
Tau Tona

4. Tilt – monitoring system and data analysis

5. Cubby Borehole Geophones (G GY & GZ) Side Wall (SW) Geophone
Tilt meters (T1 &T2)
Cubby
Borehole Geophones
(G GY & GZ)
Data recorder
Side Wall (SW)
Geophone
Footwall Wall (FW)
Pier 0.7 m into
the Footwall SW
Tilt meter

6. Mponeng Mine Level 113 Cross-cut 45
Borehole Geophones
GX, GY & GZ T2
+TX2
+TY2 T1
+TX1
+TY1 SW FW

7. Mponeng Mine Level 116 Cross-cut 45
JP/DE G3
TUNNEL y
CUBBY
T 2 x x
1.0 m x
T 1
JP/DE y BB y G1 G2
G1, G2 and G3 – CSIR geophones
T1 and T2 – CSIR Tiltmeters
BB – USGS Broadband
JP/DE – Japan/Germany Instrumentation

8. Acquisition system Dynamic section Quasi-static section
Store readings from both geophones
and tilt meters in a trigger mode
Store readings from the tilt
meters every minute

9. Coseismic and aseismic tilt
Coseismic tilt
Aseismic tilt
Time
Aseismic tilt is measured as a change in the tilt between two consecutive events

10. Coseismic and aseismic tilt

11. Tilt during the “fast” seismic event
-10 10 20 30 40 50 60 70 80
-20
-15 -5 5 15
Time (min)
Tilt (microradians)
Tilt X
Tilt Y
Tilt before 'fast' seismic event
08/02/ :45:51
Tilt after 'fast' seismic event
Before tilt
After tilt

12. Example of “slow” seismic event
Tilt before and after a "slow" seismic event (2006/07/06 07:36)
-60
-50
-40
-30
-20
-10 10 20 30 40 50
100
150
200
250
Time (minutes)
Tilt difference (microradians)
x (T1)
y (T1)
x (T2)
y (T2)
Tilt before and after a "slow" seismic event (2006/10/16 16:02)
-200
-150
-100

13. Tilt associated with M=2
Tilt associated with M=2.1 seismic event on 12/27/2007 located close to the
Site 116 Mponeng mine

14. Tilt associated with M=2
Tilt associated with M=2.1 event on 12/27/2007 located close to the Site 116, Mponeng mine

15. Tilt changes associated with M=2
Tilt changes associated with M=2.1 event on 12/27/2007 located close to the Site 116, Mponeng mine

16. Closure – monitoring system and data analysis

17. Instrumentation Closure Meter PVD Triaxial geophone meter Closure

18. Underground site at Klerksdorp area

19. Strong ground motion and closure

20. Coseismic and aseismic deformations relative to mining

22. Conclusions
The coseismic tilt and closure suddenly increase during the seismic event and blasting
Much of quasi-static deformations were found to occur independently of seismic events and were described as ‘slow’ or aseismic events
The tilt before and after a seismic event shows lack of after-tilt in most of the cases studied
The after-tilt associated with M=2.1 seismic event is a result of the aftershock sequence following the event
Coseismic deformations are associated with stress regime outside the fracture envelope while the aseismic deformations are associated with mobilization of fractures and stress relaxation within the fracture envelope

23. Thank you