Small slow‐strain steps and their forerunners observed in gold mine in South Africa

Naoi, Makoto; Ogasawara, Hiroshi; Takeuchi, J.; Yamamoto, Akihito; Shimoda, Naoyuki; Morishita, K.; Ishii, Hiroshi; Nakao, Shigeru; Aswegen, Gerrie van; Mendecki, A. J.; Lenegan, Patrick; Ebrahim-Trollope, R; Iio, Yoshihisa

doi:10.1029/2006gl026507

Cited by 18 publications

(10 citation statements)

References 6 publications

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“…The result of this study indicates the possibility of frequency-dependent increase in the seismic attenuation of transmitting waves through a fault zone before earthquakes. Naoi et al (2006) reported that aseismic slow strain steps were observed in the vicinity of the M ∼ 2 focal regions, and that these Figure 10. Normalized relative spectral amplitudes for all earthquake pairs of interest (dark grey for seismograms of events marked with asterisk in Table 1 and light grey for stacked waveforms) and synthetic ones calculated with suitable values of a and ( ε 2 ) 1/2 (black).…”

Section: Frequency Dependent Pre-seismic Changes In S-wave Attenuationmentioning

confidence: 90%

“…Naoi et al. (2006) reported that aseismic slow strain steps were observed in the vicinity of the M ∼ 2 focal regions, and that these aseismic slow strain steps increased after FebM2 and increased at a greater rate after AprM2.…”

Section: Temporal Changes In the S‐wave Attenuationmentioning

confidence: 99%

“…Although the strainmeter was installed within 10 m of the M ∼2 source fault ( Fig. 1), no strain acceleration was detected before these M ∼ 2 earthquakes (Naoi et al 2006).…”

Section: Site and Datamentioning

confidence: 99%

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Temporal changes in attenuation ofSwaves through a fault zone in a South African gold mine

Yoshimitsu

Kawakata

Yamamoto

et al. 2012

Geophysical Journal International

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SUMMARY We investigated the temporal changes in the seismic attenuation of a fault zone using near‐source recordings of S waves from repeating microearthquakes that occurred both before and after M ∼ 2 earthquakes in the Bambanani gold mine, South Africa. Because the source locations and the mechanisms of repeating earthquakes can be regarded as identical, the attenuation change can be estimated using the spectral ratios for repeating earthquake pairs. We found an increase in the S‐wave attenuation parameter on the vertical component which is positively correlated with frequency, corresponding to times before and after the M ∼ 2 earthquakes. This increase can be explained by scattering attenuation, with a typical scale of damage in the fault zone of ∼3 m.

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Section: Frequency Dependent Pre-seismic Changes In S-wave Attenuationmentioning

confidence: 90%

Section: Temporal Changes In the S‐wave Attenuationmentioning

confidence: 99%

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Temporal changes in attenuation ofSwaves through a fault zone in a South African gold mine

Yoshimitsu

Kawakata

Yamamoto

et al. 2012

Geophysical Journal International

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“…This paper presents our analysis of the seismicity around an advancing mining front using AE monitoring data in the Cooke 4 Mine (previously known as the Ezulwini Gold Mine) in South Africa. Deployed as part of the Science and Technology Research Partnership for Sustainable Development (SATREPS) program, [15][16][17][18][19][20] sensors have located AEs as small as À 4 in moment magnitude (M w ) or even smaller. We applied the joint hypocenter determination (JHD) method 21 to these AE data to improve the absolute location accuracy followed by the double difference (DD) method 22 to improve the relative location accuracy.…”

Section: Introductionmentioning

confidence: 99%

Delineation of large localized damage structures forming ahead of an active mining front by using advanced acoustic emission mapping techniques

Moriya

Naoi

Nakatani

et al. 2015

International Journal of Rock Mechanics and Mining Sciences

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a b s t r a c tWe applied advanced mapping techniques to 291 230 acoustic emission (AE) events as small as around M À 4 that were recorded over 50 days by an ultra-high resolution network close to the active front of a tabular mining stope being advanced northward at 1 km depth in the Cooke 4 Gold Mine in South Africa. We first applied joint hypocenter determination (JHD) to improve absolute locations, and then applied the double-difference relative location algorithm to the JHD output. These steps resolved the seemingly continuous, dense cloud of AEs that extend about 20 m ahead of the stope front into several discrete, steeply dipping tabular clusters a few meters thick and 10-30 m in dip extent, separated by quiet intervals a few meters thick. The clusters have a strike parallel to the stope face and a dip of about 65°, resembling commonly observed large shear fractures along the plane of maximum shear (Ortlepp shears). In general, the activity of the clusters changed in similar ways as the stope face advanced, but each cluster remained stationary and the gaps between clusters were impressively quiet. This study demonstrates that high-resolution AE mapping can delineate the formation of large structures of localized damage in the highly stressed intact rock mass ahead of the stope face, a process that may culminate in hazardous seismic events.

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“…meters (Takeuchi, 2005;Naoi et al, 2006) and several-kHz frequency-band seismometers (Yamada et al, 2005(Yamada et al, , 2007.…”

Section: Introductionmentioning

confidence: 99%

Observation of numerous aftershocks of an Mw 1.9 earthquake with an AE network installed in a deep gold mine in South Africa

Yabe

Philipp²,

Nakatani

et al. 2009

Earth Planet Sp

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This is the first report from the JAGUARS (JApanese-German Underground Acoustic Emission Research in South Africa) project, the overall aim of which is to observe ultra-small fracturing in a more or less natural environment. We installed a local (∼40-m span) network of eight acoustic emission (AE) sensors, which have the capability to observe up to 200 kHz at a depth of 3.3 km in a South African gold mine. Our specific objective was to monitor a 30-m thick dyke that remains as a dip pillar against active mining ∼90 m above our network. An M w 1.9 earthquake whose hypocenter was ∼30 m above the network occurred in the dyke. Although the mineowned geophone (4.5 Hz) network detected only five earthquakes in the surrounding 200×200×150-m 3 volume within the first 150 h following the main shock, our AE network detected more than 20,000 earthquakes in the same period. More than 13,000 of these formed a distinct planar cluster (∼100×80 m 2 ) on which the main shock hypocenter lay, suggesting that this cluster delineates the main shock rupture plane. Most of the aftershocks were presumably very small, probably as low as M ∼ −4. The aftershock cluster dipped ∼60• . This is consistent with normal faulting under a nearly vertical compression field, as indicated by nearly horizontal breakouts found in a borehole crossing the rupture plane.

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Small slow‐strain steps and their forerunners observed in gold mine in South Africa

Cited by 18 publications

References 6 publications

Temporal changes in attenuation ofSwaves through a fault zone in a South African gold mine

Temporal changes in attenuation ofSwaves through a fault zone in a South African gold mine

Delineation of large localized damage structures forming ahead of an active mining front by using advanced acoustic emission mapping techniques

Observation of numerous aftershocks of an Mw 1.9 earthquake with an AE network installed in a deep gold mine in South Africa

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