g. kwiatek and jaguars research group

To understand earthquake rupture process in picoscale: Two To understand earthquake rupture process in picoscale: Two years of high-frequency seismic monitoring at the years of high-frequency seismic monitoring at the Mponeng gMponeng gold old

mine in South Africamine in South Africa

G. Kwiatek and JAGUARS Research Group

AIM Workshop, Prague, 29-30 September 2011

Aims of JAGUARS projectAims of JAGUARS project▶Investigate the self similarity of earthquake rupture process▶Link laboratory studies and nano-picoseismicity recorded in-situ

Courtesy of E. Charalampidou; W.D. Ortlepp, RaSiM5 proceedings; Wikipedia

cm-scale m-scale km-scale


Mponeng „Look with pride” deep gold mineMponeng „Look with pride” deep gold mine

JAGUARS materials, google maps, Anglogold Ashanti materials


JAGUARS in-situ geomechanical laboratoryJAGUARS in-situ geomechanical laboratory▶Depth 3540m; vicinity of a dyke and active mining (exploitation level ~90m above the network). Small area (300x300x300m) monitored.

N

A B


AE-sensor

JAGUARS materials (M. Nakatani)AIM Workshop, Prague, 29-30 September 2011

NetworkNetwork

▶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


Accelerometer (ACC)Accelerometer (ACC)▶Developed by ISS (now IMS)▶3-component and 1-component sensors▶Sensitivity between 50Hz-25000Hz

JAGUARS materials


Acoustic emission (AE) sensorsAcoustic emission (AE) sensors▶Developed by Gesellschaft für Materialprüfung und Geophysik (GMuG mbH) ▶Installation & coupling issues

JAGUARS materials (M. Nakatani)


Network sensitivityNetwork 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)


Seismic data | Aftershock sequenceSeismic data | Aftershock sequence▶MW1.9 30m from the network, followed by 25,000 aftershocks

▶No accelerating activity (immediate foreshocks) before the main event

(Naoi et al., 2011, Bull Seism. Soc. Am. 101 (5); Focal mechanism calculated by M. Boettcher, Univ. New Hampshire

Before mainshock After mainshock


Madariaga!

Seismic data | Aftershock sequenceSeismic data | Aftershock sequence▶Aftershock activity follows Gutenberg-Richter scaling relation▶b=1.26, Mc=-4.30 for the fault plane (F)

(Kwiatek et al., 2010, Bull. Seism. Soc. Am. 100)

b=1.26

MC=-4.30


Seismic data | Post-blasting activitySeismic 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)


Seismic data | Post-blasting activitySeismic data | Post-blasting activity▶Post-blasting also follows scaling relations with b=1.16

(Kwiatek et al., 2010, Bull. Seism. Soc. Am. 100)


Extensive scaling relation studyExtensive 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)

Scaling relations Scaling relations (stress drop)(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



Scaling relations Scaling relations (apparent stress)(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



Tired of self-similarity and scaling relations?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, 2011b, Phys. Res. Lett., in preparation)

(Davidsen & Kwiatek, 2011a, Phys. Res. Lett., submitted)


Evidences for slow rupturesEvidences 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

▶ Influences stress drop/apparent stress values!!!


This ratio youtypically observe


Non-double-couple componentsNon-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)


Shear Tensile


Variations in stress drop and apparent stressVariations in stress drop and apparent stress▶Depends on geological setup (cracked/isotropic)▶Various rupture velocities?



SummarySummary

▶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 time-dependent 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.


Thank you for your attention!

AcknowledgmentsAcknowledgmentsThe The Rock EngineeringRock Engineering and and GeologyGeology departments (R. Carstens, C. Miller, M. Pienaar and G. Flitton) departments (R. Carstens, C. Miller, M. Pienaar and G. Flitton) at Mponeng gold mine at Mponeng gold mine (AngloGold Ashanti), (AngloGold Ashanti), ISS CarletonvilleISS Carletonville, , ISS Stellenbosch ISS Stellenbosch and and CSIR Johannesburg CSIR Johannesburg are acknowledged for providing us with are acknowledged for providing us with many useful information and electronic materials.many useful information and electronic materials. We would like to thank R. Barth,We would like to thank R. Barth, O. Germer, L. Vasquez and M. O. Germer, L. Vasquez and M. Wieprich for helping us with the manual preparation of the dataset.Wieprich for helping us with the manual preparation of the dataset. Y. Ben-Zion is acknowledged for many valuable Y. Ben-Zion is acknowledged for many valuable discussions.discussions.


g. kwiatek and jaguars research group

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