Wave attenuation in South African gold mines

• We investigated temporal changes in seismic attenuation of S waves from small earthquakes that pass through a fault zone, including the source regions of M~2 earthquakes that occurred in February and April 2003, in the Bambanani gold mine, South Africa. Repeating microearthquakes, whose source locations and mechanisms can be regarded to be identical, occurred both before and after the M~2 earthquakes. We calculated the spectral ratios of S waves for the repeating earthquake pairs which were recorded by a closely situated geophone.
  
  We found an increase in the S wave attenuation for frequencies higher than 100 Hz, corresponding to times after the M~2 earthquakes. This can be explained by an increment of scattering attenuation with the characteristic scale of damage in the fault zone. Moreover, we also found a weak increase in the S-wave attenuation across the fault zone prior to the M~2 earthquakes, with a similar characteristic scale of damage.
  
  
  Normalized relative spectral amplitudes for all earthquake pairs of interest (gray) and synthetic ones (black), (a) in the period which contain no earthquakes, (b)(c) in the period prior to the M2 earthquakes, (d)(e) in the priod which contain M2 earthquakes.
  
  See Yoshimitsu et al. (2012) for a detailed description.
  Temporal changes in attenuation of S waves through a fault zone in a South African gold mine