HR: 0800h
AN: S41B-0965 [Abstracts]
TI: Apparent Stresses of Mining Earthquakes with Seismic Moments of $10^{8}
EM: yoshimura@hakusan.s.kanazawa-u.ac.jp
AF: Gradurate school of Natural science and Technology, Kakuma, Kanazawa, 920-1192
AU: HIRAMATSU, Y
EM: yoshizo@hakusan.s.kanazawa-u.ac.jp
AF: Gradurate school of Natural science and Technology, Kakuma, Kanazawa, 920-1192
AU: FURUMOTO, M
EM: furumoto@hakusan.s.kanazawa-u.ac.jp
AF: Gradurate school of Natural science and Technology, Kakuma, Kanazawa, 920-1192
AB:
Mining at a deeper part in the crust usually causes micro- to small earthquakes in the close vicinity of stopes. Seismogenic
processes of earthquakes can be monitored at very short hypocentral distances with sensors installed in seismogenic areas.
However, it has been controversial if a mining earthquake and an ordinary earthquake can be treated as an identical
earthquake phenomenon. Richardson and Jordan(2002) shows that mining earthquakes are classified into two kinds from their
characteristics and that the two kinds are different in a scaling relation between the apparent stress and the seismic
moment. The purpose of this report is to determine precise apparent stresses of many mining events using high quality data
and to compare them with those of natural earthquakes.
To observe mining events, nine three components borehole accelerometers were installed in Precambrian quartzite (typical
Young's modulus of 70Gpa) within 200 m along a haulage tunnel at a depth of 2650m in Mponeng mine in South Africa. The
observation was carried out from February to December in 1996. More than 25 thousand seismic events were recorded with a
sampling frequency of 15 kHz and a dynamic range of 120 dB. We selected 378 events with high S/N from the events. The
hypocentral distance of the events, which are determined by assuming an infinite medium with the P-wave velocity 5.5 km/s and
the S-wave velocity 3.2 km/s, are in a range of 15m to 1km. We estimate the apparent stress $\Delta \sigma _a$ of the events
by applying the same method that was used by Ide and Beroza(2001).
The obtained apparent stresses of the mining events are $0.4< \Delta \sigma _a<8MPa$ for events with the seismic moments
$10^{8}
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting