Rayleigh wave and well head response to calculate porosity in the Edwards aquifer of south-central Texas, USA
We use the magnitude and period of Rayleigh wave along with the fluctuation amplitude of well head to calculate effective porosity of karst aquifers at site scale. The radial and vertical displacements of Rayleigh wave are at first related to the confining pressure which is then related to fluid pressure via Gassmann equation. Three seismograms recorded at station 633A of USARRAY and the induced responses of Well J-17 in the Edwards Aquifer, Texas, result in an effective porosity between 17.0 and 24.4 percent, the average of which is close to the total porosity determined by geophysical well logs. This paper provides a very new method to measure effective porosity in aquifers. Because of the large wavelength of Rayleigh wave, the interdisciplinary method is advantageous in that second porosity represented by large conduits and voids can be detected.