AQUIFER STORAGE PROPERTIES GENERATED FROM GROUNDWATER RESPONSES TO SEISMIC RAYLEIGH WAVES IN THE GRANDE RONDE AQUIFER, PALOUSE GROUNDWATER BASIN

A direct comparison between measurable groundwater fluctuations induced by seismic waves from large global earthquakes has previously been shown to be useful for evaluating specific storage of aquifers. A new computation procedure has been developed to deal with the sparse amount of water level data relative to seismological data. The method demonstrates that, given the transmissivity of a confined uniformly porous aquifer, a single water level deflection measurement, if normalized to an appropriately filtered power spectrum of the associated Rayleigh wave motion, can provide a rough but unbiased estimate of the aquifer specific storage. Given a sufficient number of appropriate water level measurements during the passage of Rayleigh waves, specific storage can be computed to a similar accuracy as for continuous water level data. As a result of calculating the Rayleigh wave spectrum independently for each water level measurement during earthquakes, results from multiple earthquakes can be superposed to ensure a low computational error. Of course, the overall accuracy of the method depends not only on the computation procedure but also on the fit of the aquifer to the initial assumptions and on the extent to which the aquifer transmissivity is known.