Tidal influence on self-potential measurements

D. J. MacAllister, M. D. Jackson, A. P. Butler, J. Vinogradov

Research output: Contribution to journalArticle

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Abstract

Long-term surface and borehole self-potential (SP) monitoring was conducted in the UK Chalk aquifer at two sites. The coastal site is c. 1.7 km from the coast and the inland site is c. 80 km from the coast. At both sites, power spectral density analysis revealed that SP data contain the main ocean tidal periodic components. However, the principal lunar component (M2), the dominant ocean tidal component, was most significant at the coastal site. The M2 signal in surface-referenced SP data at the inland site was partly due to telluric currents caused by the geomagnetic ocean dynamo. Earth and/or atmospheric tides also contributed, as the SP power spectrum was not typical of a telluric electric field. The M2 component in borehole-referenced data at the inland site was below the significance level of the analysis method and was two orders of magnitude smaller than the M2 signal in borehole-referenced SP data at the coastal site. The tidal response of the SP data in the coastal borehole is, therefore, primarily driven by ocean tides. These cause changes in fluid pressure and chemical concentration gradients within the coastal aquifer, leading to time varying electrokinetic and exclusion-diffusion potentials. Borehole-referenced SP measurements could be used to characterize and monitor tidal processes in coastal aquifers such as the intrusion of seawater.
Original languageEnglish
Pages (from-to)8432–8452
Number of pages21
JournalJournal of Geophysical Research: Solid Earth
Volume121
Issue number12
Early online date10 Nov 2016
DOIs
Publication statusPublished - 1 Dec 2016

Fingerprint

self potential
Boreholes
boreholes
Aquifers
borehole
Tides
aquifers
oceans
Coastal zones
coastal aquifer
coasts
Calcium Carbonate
ocean
Power spectral density
Power spectrum
atmospheric tide
Seawater
atmospheric tides
telluric currents
ocean tide

Keywords

  • self-potential
  • hydrogeophysics
  • tides
  • groundwater hydrology
  • electrokinetic potential
  • exclusion-diffusion potential
  • instruments and techniques : monitoring
  • magnetic and electrical methods
  • water management

Cite this

Tidal influence on self-potential measurements. / MacAllister, D. J. ; Jackson, M. D.; Butler, A. P. ; Vinogradov, J.

In: Journal of Geophysical Research: Solid Earth, Vol. 121, No. 12, 01.12.2016, p. 8432–8452 .

Research output: Contribution to journalArticle

MacAllister, D. J. ; Jackson, M. D. ; Butler, A. P. ; Vinogradov, J. / Tidal influence on self-potential measurements. In: Journal of Geophysical Research: Solid Earth. 2016 ; Vol. 121, No. 12. pp. 8432–8452 .
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note = "DJM was supported by NERC CASE studentship NE/I018417/1. The authors would also like to thank Southern Water for access to the borehole at Saltdean. Atkins Global and Southern Water are thanked for funding installation of the equipment and for additional funding under the NERC studentship. The laboratory components of this work were carried out in the TOTAL Reservoir Physics Laboratory at Imperial College London and their support is gratefully acknowledged. Jackson acknowledges partial support from TOTAL under the TOTAL Chairs programme. The data supporting the conclusions of this work are available through the corresponding author.",
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N2 - Long-term surface and borehole self-potential (SP) monitoring was conducted in the UK Chalk aquifer at two sites. The coastal site is c. 1.7 km from the coast and the inland site is c. 80 km from the coast. At both sites, power spectral density analysis revealed that SP data contain the main ocean tidal periodic components. However, the principal lunar component (M2), the dominant ocean tidal component, was most significant at the coastal site. The M2 signal in surface-referenced SP data at the inland site was partly due to telluric currents caused by the geomagnetic ocean dynamo. Earth and/or atmospheric tides also contributed, as the SP power spectrum was not typical of a telluric electric field. The M2 component in borehole-referenced data at the inland site was below the significance level of the analysis method and was two orders of magnitude smaller than the M2 signal in borehole-referenced SP data at the coastal site. The tidal response of the SP data in the coastal borehole is, therefore, primarily driven by ocean tides. These cause changes in fluid pressure and chemical concentration gradients within the coastal aquifer, leading to time varying electrokinetic and exclusion-diffusion potentials. Borehole-referenced SP measurements could be used to characterize and monitor tidal processes in coastal aquifers such as the intrusion of seawater.

AB - Long-term surface and borehole self-potential (SP) monitoring was conducted in the UK Chalk aquifer at two sites. The coastal site is c. 1.7 km from the coast and the inland site is c. 80 km from the coast. At both sites, power spectral density analysis revealed that SP data contain the main ocean tidal periodic components. However, the principal lunar component (M2), the dominant ocean tidal component, was most significant at the coastal site. The M2 signal in surface-referenced SP data at the inland site was partly due to telluric currents caused by the geomagnetic ocean dynamo. Earth and/or atmospheric tides also contributed, as the SP power spectrum was not typical of a telluric electric field. The M2 component in borehole-referenced data at the inland site was below the significance level of the analysis method and was two orders of magnitude smaller than the M2 signal in borehole-referenced SP data at the coastal site. The tidal response of the SP data in the coastal borehole is, therefore, primarily driven by ocean tides. These cause changes in fluid pressure and chemical concentration gradients within the coastal aquifer, leading to time varying electrokinetic and exclusion-diffusion potentials. Borehole-referenced SP measurements could be used to characterize and monitor tidal processes in coastal aquifers such as the intrusion of seawater.

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