Tunnel Seismic Reflection Survey Planning Using 3D Numerical Simulations at South Deep Gold Mine, South Africa

Abstract

Summary In this study we use 3D numerical simulations to show how seismic wavefields propagate in deep gold mining environments. In order to do this, we computed a 3D seismic survey using realistic source and receiver parameters as well as existing geological models of the site. We position the source at depth of 3 km below surface in a working tunnel and the receivers are placed on surface. As the wavefield propagates from underground towards the surface, low amplitude reflections can be observed as it moves from quartzite to lava. The seismic waves experience less interference when travelling from lava to dolomite, this can be attributed to the lesser acoustic impedance contrast between the two mediums. When the wavefield interacts with the in-mine working tunnels, it undergoes rapid peak particle velocity (PPV) variations and multiple mode conversions. We attribute these PPV variations to the high velocity and density contrast between the tunnels and the surrounding lithologies. It is through the numerical simulations that we can characterize wavefield interactions using a variety of survey acquisition parameters. As a result we can rely on numerical simulations to give us estimates of the different wavefield responses for real seismic surveys of this kind.