We have investigated the distribution and thickness of damage zones for a system of secondary normal faults in the subsurface of the Wangxuzhuang oilfield, China. Based on seismic variance analysis, we find (1) four isolated faults with approximately 2 km length and approximately 200 m damage-zone thickness. The damage zones of these isolated faults reveal a decaying intensity of deformation from the fault core to the protolith, which fits a power-law form similar to that observed in the field. (2) A merged fault with approximately 400 m thickness. (3) A bifurcated fault with approximately 400 m thickness and three linked segments. Damage zones that consist of several subsidiary faults are thicker than those of isolated faults. The displacement-length analyses of the four isolated faults suggest the constant-length growth of the limestone in this case. We determine the potential to apply seismic variance to systematically characterize damage zones as potential fluid migration conduits on the basin scale.