Transcript (Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in

To understand earthquake rupture process in picoscale: Two
years of high-frequency seismic monitoring at the Mponeng gold
mine in South Africa
G. Kwiatek and JAGUARS Research Group
AIM Workshop, Prague, 29-30 September 2011
Aims of JAGUARS project
▶Investigate the self similarity of earthquake rupture process
▶Link laboratory studies and nano-picoseismicity recorded in-situ
cm-scale
m-scale
km-scale
Courtesy of E. Charalampidou; W.D. Ortlepp, RaSiM5 proceedings; Wikipedia
AIM Workshop, Prague, 29-30 September 2011
Mponeng „Look with pride” deep gold mine
JAGUARS materials, google maps, Anglogold Ashanti materials
AIM Workshop, Prague, 29-30 September 2011
JAGUARS in-situ geomechanical laboratory
▶Depth 3540m; vicinity of a dyke and active mining (exploitation level ~90m above
the network). Small area (300x300x300m) monitored.
A
N
AIM Workshop, Prague, 29-30 September 2011
B
AE-sensor
JAGUARS materials (M. Nakatani)
AIM Workshop, Prague, 29-30 September 2011
Network
▶8 Acoustic emission (AE)
sensors (1kHz-170kHz)
▶One 3C, high frequency
accelerometer (0.05-25kHz)
▶Located in boreholes
▶Triggering mode
▶In-situ location and
acquisition
▶Sampling frequency 500kHz
AIM Workshop, Prague, 29-30 September 2011
Accelerometer (ACC)
▶Developed by ISS (now IMS)
▶3-component and 1-component sensors
▶Sensitivity between 50Hz-25000Hz
JAGUARS materials
AIM Workshop, Prague, 29-30 September 2011
Acoustic emission (AE) sensors
▶Developed by Gesellschaft für
Materialprüfung und Geophysik
(GMuG mbH)
▶Installation & coupling issues
JAGUARS materials (M. Nakatani)
AIM Workshop, Prague, 29-30 September 2011
Network sensitivity
▶System capable of recording MW -4.5 (source size of few cm) @ ~80m
▶Significant damping & scattering due to local engineering structures
▶Strong variations in magnitude of completeness
(Plenkers, Schorlemmer, Kwiatek, 2011, Bull. Seism. Soc. Am. 101 (6), in press)
AIM Workshop, Prague, 29-30 September 2011
Seismic data | Aftershock sequence
▶MW1.9 30m from the network, followed by 25,000 aftershocks
▶No accelerating activity (immediate foreshocks) before the main event
Before mainshock
After mainshock
Madariaga!
(Naoi et al., 2011, Bull Seism. Soc. Am. 101 (5); Focal mechanism calculated by M. Boettcher, Univ. New Hampshire
AIM Workshop, Prague, 29-30 September 2011
Seismic data | Aftershock sequence
▶Aftershock activity follows Gutenberg-Richter scaling relation
▶b=1.26, Mc=-4.30 for the fault plane (F)
MC=-4.30
b=1.26
(Kwiatek et al., 2010, Bull. Seism. Soc. Am. 100)
AIM Workshop, Prague, 29-30 September 2011
Seismic data | Post-blasting activity
▶Post-blasting activity starts right after blasting (~6-7pm). The Omori decay is visible
even 12 hours after blasting.
(Plenkers & Kwiatek, 2010, Seismological Research Letters 81)
AIM Workshop, Prague, 29-30 September 2011
Seismic data | Post-blasting activity
▶Post-blasting also follows scaling relations with b=1.16
(Kwiatek et al., 2010, Bull. Seism. Soc. Am. 100)
AIM Workshop, Prague, 29-30 September 2011
Extensive scaling relation study
▶Gutenberg-Richter scaling relation
▶Static and dynamic scaling relations
(stress drop vs seismic moment,
apparent stress vs seismic moment)
▶Magnitude clustering and
interevent time clustering
Selection for source parameters:
Post-blasting activity, aftershocks
located far away
Analysis:
Spectral fitting + spectral ratio
(Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press)
AIM Workshop, Prague, 29-30 September 2011
Scaling relations
(stress drop)
► Constant static stress drop
scaling relation observed
between MW -0.8 and -4.1
▶ Frequency range 500-17kHz
(source radius 4m-5cm)
▶ Rupture proces self-similar
(Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press)
AIM Workshop, Prague, 29-30 September 2011
Scaling relations
(apparent stress)
▶Uniform energy release per unit
slip and unit area
▶Rupture process self-similar
▶Second-order disturbances
identified as originating from
limited frequency band
(Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press)
AIM Workshop, Prague, 29-30 September 2011
Tired of self-similarity and scaling relations?
▶We found no evidence for time-dependent magnitude clustering both for
aftershock sequence of MW1.9 event and post-blasting activity.
–Assumption of time-independent magnitudes is justified
–Existence of magnitude correlations is an artificact related to catalog incompleteness
–Important for statistical models e.g. PSHA or ETAS-related
▶We found no evidence for correlation between subsequent interevent times both
for foreshocks of MW1.9 event and natural seismic activity
(Davidsen & Kwiatek, 2011a, Phys. Res. Lett., submitted)
(Davidsen & Kwiatek, 2011b, Phys. Res. Lett., in preparation)
AIM Workshop, Prague, 29-30 September 2011
Evidences for slow ruptures
▶Low corner frequency fP/fS ratio
observed
▶Rupture governed by rupture time
(low rupture velocity preferred)
Low radiation efficiency observed
▶ Suggest low rupture velocity
This ratio you
typically observe
▶ Influences stress drop/apparent stress values!!!
(Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press)
AIM Workshop, Prague, 29-30 September 2011
Non-double-couple components
▶Low ES/EP ratio observed in the whole magnitude range
▶Many events possibly display a non-DC behavior
▶Work in progress (co-op with Y. Ben-Zion)
Tensile Shear 
(Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press)
AIM Workshop, Prague, 29-30 September 2011
Variations in stress drop and apparent stress
▶Depends on geological setup (cracked/isotropic)
▶Various rupture velocities?
(Kwiatek et al., 2011, Bull. Seism. Soc. Am. 101 (6), in press)
AIM Workshop, Prague, 29-30 September 2011
Summary
▶The combined AE-ACC network allowed to bridge the gap between laboratory
experiments on rock samples and induced seismicity.
▶Earthquake rupture process is governed by similar physics over a range of
magnitudes between laboratory experiments and small earthquake. This is
supported by G-R relation, dynamic and static source parameters and timedependent statistical analysis of magnitude clustering and event-time interval
▶Local variations in stress drop and apparent stress clearly depend on geological
setup. Rupture velocity must be addressed in future works on scaling relations
(Brodsky & Kanamori, AGU Monograph).
▶We reached the frequency limit of the recording system calibrated in an absolute
sense that allows to calculate reliably the source parameters.
AIM Workshop, Prague, 29-30 September 2011
Thank you for your attention!
Acknowledgments
The Rock Engineering and Geology departments (R. Carstens, C. Miller, M. Pienaar and G. Flitton) at Mponeng gold mine
(AngloGold Ashanti), ISS Carletonville, ISS Stellenbosch and CSIR Johannesburg are acknowledged for providing us with
many useful information and electronic materials. We would like to thank R. Barth, O. Germer, L. Vasquez and M.
Wieprich for helping us with the manual preparation of the dataset. Y. Ben-Zion is acknowledged for many valuable
discussions.
AIM Workshop, Prague, 29-30 September 2011