Surface waves are often looked at as noise when a seismic survey is performed to evaluate the subsurface. However, when a natural seismic event of maginude 7.0 or greater occurs, the surface waves produced still have large amplitude even after traveling great distances. Large Rayleigh wave amplitudes can produce measurable water-level changes in confined aquifers. Calculated pressures from Rayleigh waves can then be used to estimate specific storage of aquifers through a seismic-efficiency calculation, in a similar method to barometric-efficiency and tidal-efficiency calculations. The seismic-efficiency method has benefits over other methods of determining specific storage such as requiring a shorter period of data record. Calculations of specific storage for the Balcones Fault Zone of the Edwards Aquifer using the seismic-efficiency method show a range in specific storage from 2.80E-07 to 3.82E-06 ft-1. These results have been statistically compared to barometric efficiency values calculated for the same wells. Storativity varies from 1.40E-04 to 2.68E-03 across the aquifer, which is an estimate of the heterogeneity of storativity in the Balcones Fault Zone aquifer. By comparison, most models assume uniform storativity.