Microseismicity and Acoustic Emission in Deep Gold Mine in South Africa
The study of faulting and rupture processes requires direct observations. In the Earth crust deep mines provide a unique opportunity for this purpose by giving access to the focal depth of earthquakes. To investigate the physics of earthquakes and link laboratory and seismological observations, the JAGUARS (Japanese-German Acoustic Emission Research in South Africa) Working Group was established. The JAGUARS project continuously monitors microseismic activity at 3.5km depth in Mponeng gold mine, Republic of South Africa.
The deep gold mine is a unique natural laboratory to study kinematic and dynamic properties both of source and propagation of seismic events, fault properties as well as stress conditions. The seismic monitoring can provide direct observations of local instabilities in the rock mass induced by mine excavations and in existing geological structures such as dyke contacts or natural faults.
JAGUARS’ network is located 90m below the gold reef, where intensive mining is performed next to the pink dyke which is a major local geologic feature. The major components of the network are currently 8 acoustic emission sensors (denoted AE, see figure), one three-component accelerometer (ACC-36) and two strainmeters. The sampling frequency of the acquisition system is 500 kHz and the total frequency range recorded is between 50Hz and 200 000Hz. The whole system works in triggering mode.
In the time period end of May 2007 and beginning of April, 2008 almost 300,000 events were successfully recorded from which more then 84000 were automatically located by the systems software. In general, high frequency events (>40 kHz) are recorded from distances up to 50m from the network. Events with frequencies below 40kHz are recorded from distances up to 400m. The analysis of events recorded is on-going.
In future larger scale measurements are also planned within the NELSAM-project at TauTona-Mine.