Borehole-to-borehole hydrologic response across 2.4 km in the upper oceanic crust: Implications for crustal-scale properties

A. T. Fisher, E. E. Davis, Keir Becker

Research output: Contribution to journalArticle

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Abstract

Subseafloor hydrologic observatories (CORKs) were installed in four boreholes in young seafloor on the eastern flank of the Juan de Fuca ridge to evaluate the hydrogeology of the upper oceanic crust. Two CORKs installed at Site 1301 were incompletely sealed, allowing cold bottom water to flow into basement at 2-5 L/s and causing a pressure perturbation in a preexisting sealed CORK at Site 1027, which was 2.4 km away. The pressure perturbation at Site 1027 is analyzed using conventional aquifer test methods, yielding transmissivity of T = 0.5 to 1.2 × 10-2 m2/s and bulk permeability of k = 0.7 to 2 × 10-12 m2 in the upper 300 m of basement. Storativity (a parameter that includes fluid and aquifer compressibilities, porosity, and layer thickness) is S = 1 to 3 × 10-3, corresponding to a crustal aquifer (matrix) compressibility of βm = 3 to 9 × 10-10 Pa-1. The inferred basement permeability is consistent with, but at the low end of, permeabilities calculated from single-hole packer experiments at this and other young oceanic crustal sites; it is much less than values estimated from numerical models, analyses of formation response to tidal pressure oscillations, or pressure responses to coseismic strain events. The relatively low permeability indicated by the cross-hole response may result from the basement aquifer in this area being azimuthally anisotropic, with a preferential flow direction oriented subparallel to the abyssal hill topography and tectonic structural fabric created at the ridge axis; this hypothesis will be tested during future experiments.

Original languageEnglish (US)
Article numberB07106
JournalJournal of Geophysical Research C: Oceans
Volume113
Issue number7
DOIs
StatePublished - Jul 4 2008

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aquifers
boreholes
Boreholes
Aquifers
basements
upper crust
oceanic crust
crusts
permeability
borehole
aquifer
compressibility
Compressibility
ridges
hydrogeology
perturbation
abyssal hill
Hydrogeology
pressure oscillations
Packers

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science
  • Atmospheric Science
  • Astronomy and Astrophysics
  • Oceanography

Cite this

Borehole-to-borehole hydrologic response across 2.4 km in the upper oceanic crust : Implications for crustal-scale properties. / Fisher, A. T.; Davis, E. E.; Becker, Keir.

In: Journal of Geophysical Research C: Oceans, Vol. 113, No. 7, B07106, 04.07.2008.

Research output: Contribution to journalArticle

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