Relating high-resolution tilt measurements to the source displacement of an M2.2 event located at Mponeng gold mine
P Share, A Milev, R Durrheim, J Kuijpers, H Ogasawara
As part of JAGUARS (JApanese-German Underground Acoustic
emission Research in South Africa), high-resolution tiltmeters were
installed during 2007 at Mponeng gold mine, South Africa, in an
attempt to study and understand the risks posed by in-mine seismic
events and to subsequently use the knowledge gained to mitigate
these risks. In December 2007, an M2.2 event occurred at Mponeng
and was detected by the tiltmeters installed. The tilt expected for the
M2.2 event is modelled through the use of numerical and analytical
tools and utilizing, as input parameters, characteristics of the event
such as the rupture area, the amount of slip, elastic properties of the
rock, the state of stress before the event occurred, and frictional
parameters of the rupture. The calculated tilt values are correlated
and compared with the recorded data, and are found to be of the
same order. Certain input parameters, such as the initial rupture
point, are further constrained by varying them, during modelling,
until the calculated and observed tilt values are approximately equal.
From modelling, it can be concluded that the rupture point had to be
closer to the location of the tiltmeters. In addition, possible locations
acting as source areas for the observed aftertilt are determined.
Further modelling still needs to be done to quantify the effects of the
tunnel close to the tiltmeters and plastic deformation of the rock
mass.
Keywords: high-resolution tilt data, Mponeng gold mine, M 2.2 seismic event,
analytical modeling, numerical modeling, rupture plane.