Temporal changes in attenuation of S waves through a fault zone in a South African gold mine



We investigated the temporal changes in the seismic attenuation of a fault zone using near-source recordings of S waves from repeating microearthquakes that occurred both before and after M ∼ 2 earthquakes in the Bambanani gold mine, South Africa. Because the source locations and the mechanisms of repeating earthquakes can be regarded as identical, the attenuation change can be estimated using the spectral ratios for repeating earthquake pairs. We found an increase in the S-wave attenuation parameter inline image on the vertical component which is positively correlated with frequency, corresponding to times before and after the M ∼ 2 earthquakes. This increase can be explained by scattering attenuation, with a typical scale of damage in the fault zone of ∼3 m.