TY - JOUR
T1 - Observation of numerous aftershocks of an Mw 1.9 earthquake with an AE network installed in a deep gold mine in South Africa
AU - JAGUARS
AU - Yabe, Yasuo
AU - Philipp, Joachim
AU - Nakatani, Masao
AU - Morema, Gilbert
AU - Naoi, Makoto
AU - Kawakata, Hironori
AU - Igarashi, Toshihiro
AU - Dresen, Georg
AU - Ogasawara, Hiroshi
N1 - Funding Information:
Acknowledgments. Comments by M. Boettcher, the University of New Hampshier, and by an anonymous reviewer were useful to improve the quality of this manuscript. Permission has been given by the Mponeng gold mine, AngloGold Ashanti Ltd, to publish some of the mine’s data. This study was partly supported by Grant-in-Aid for Scientific Research (A-18253003, A-14204040, B-18403007), the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan under its Observation and Research Program for Prediction of Earthquakes and Volcanic Eruptions, Earthquake Research Institute cooperative research program, and Tohoku University’s 21st Century COE program.
Publisher Copyright:
© 2009, Springer Berlin Heidelberg. All Rights reserved.
PY - 2009/10
Y1 - 2009/10
N2 - 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 Mw 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-m3 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 m2) 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.
AB - 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 Mw 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-m3 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 m2) 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.
KW - Acoustic emission
KW - Aftershocks
KW - Deep South African gold mines
KW - Main shock rupture plane
KW - Mining-induced earthquake
KW - Semi-controlled earthquake generation experiment
UR - http://www.scopus.com/inward/record.url?scp=84889711328&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84889711328&partnerID=8YFLogxK
U2 - 10.1186/BF03352963
DO - 10.1186/BF03352963
M3 - Letter
AN - SCOPUS:84889711328
VL - 61
SP - e49-e52
JO - Earth, Planets and Space
JF - Earth, Planets and Space
SN - 1343-8832
IS - 10
ER -