GENERATING AQUIFER SPECIFIC STORAGE FROM GROUNDWATER RESPONSES TO SEISMIC RAYLEIGH WAVES

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. However, most groundwater data loggers are set to record measurements several orders of magnitude too slow for comprehensive comparison with seismic shaking. A new computation procedure has been developed to deal with this sparse amount of water level data relative to seismological data. The method is applicable for water level data collected in a particular well for which a good estimate of aquifer transmissivity is available. The method demonstrates that water level deflection measurements during a single earthquake, 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.