GNGTS 2013 - Atti del 32° Convegno Nazionale

high input impedance (1TΩ) buffer amplifiers. The system was tested in the field to monitor the SP anomalies due to the fluctuations of the sea level during tides. It is seen that the combination of various sources of SP due to the tides can affect the SP response with time. These effects are most likely due to the electrokinetic effect and diffusion potentials induced by the tidal fluctuations. The graphite electrodes used in this work for SP acquisition are proven to be stable in laboratory. In the field they were not subjected to relevant drifts over the entire duration of acquisition (10 days), as well. Acknowledgements. Many thanks to professor Marco Vannini (University of Firenze) for getting us involved in this project and to professor Nicola Casagli (University of Firenze) for letting us take part in the summer scientific expedition. We are grateful to professor Gabriella Losito (University of Firenze) and professor Stefano Mancuso (University of Firenze) for discussing with us about several aspects of the instrumentation. Special thanks also to Eng. Riccardo Susini (National Instrument) for his technical assistance. The assembly work could not have been done without the collaboration of Nadia Bazihizina, Alessandro Anastassopoulos and Francesco Spennati. We also wish to express gratitude to the people who contributed to the field work in Kenya: Giorgia Campiero, Stefano Giannotti, Giulia Giberti, Veronica Lisini Baldi, Alessia Lotti, Alessio Raspanti, Leonardo Terreni, and the Kenyan guides of Mida Creek. References Clerc, G., Petiau G., Perrier F.; 1998: The Garchy 1995-1996 electrode experiment technical report. INSU-CNRS/CEA, Paris. Corry C.E., De Moully G.T., Gerety M.T.; 1983: Field Procedure Manual for Self-Potential Surveys. Z.E.R.O. Publishing, Arizona, USA. Corwin R. F., Hoover D.B.; 1979: The self-potential method in geothermal exploration. Geophysics, 44 , 226 – 245, doi: 10.1190/1.1440964. Di Maio R., Di Sevo V., Giammetti S., Patella D., Piscitelli S., Silenziario C.; 1996: Self-potential anomalies in some Italian volcanic areas. Annals of Geophysics, 39 (1) , 179-188, doi: 10.4401/ag-3960. Fournier C.; 1989: Spontaneous potentials and resistivity surveys applied to hydrogeology in a volcanic area: case history of the Chaıˆnedes Puys (Puy-de-Doˆme,France). Geophys. Prosp., 37 (6) , 647–668, doi: 10.1111/j.1365-2478.1989. tb02228.x. Jardani A., Revil A., Bolève A., Dupont J.P., Barrash W., Malama B.; 2007: Tomography of groundwater flow from self- potential SP data. Geophysical Research Letters, 34 , L24403, doi: 10.1029/2007GL031907. Jouniaux L., Maineult A., Naudet V., Pessel M., Sailhac P.; 2009: Review of self-potential methods in hydrogeophysics. C.R. Geoscience, 341 (10-11) , 928-936, doi: 10.1016/j.crte.2009.08.008. Fig. 3 – On the top the tide data (black dots) obtained from the Tide Table of Mombasa harbour, the reconstructed sea level (dashed black line) and the sea level in Mida Creek (solid black line) obtained shifting in time the reconstructed sea level to match the delayed arrival of the tide in Mida Creek recorded by on-site sea level measurements. On the bottom the time-lapse mapping of the SP anomalies obtained from the data at five different time instants (a-e). 142 GNGTS 2013 S essione 3.2

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