1887

Abstract

Summary

A near-vertical hydrothermally active fault zone, embedded in sheared and fractured crystalline rocks of the Central Swiss Alps, has been drilled and geophysically explored in view of its potential similarities with planned petrothermal reservoirs in the Northern Alpine foreland. The GDP1 Grimsel Pass borehole acutely intersects the core of Grimsel Breccia Fault and is situated entirely within its surrounding deformation zone. Pervasive brittle deformation, which overprints Alpine shear zones is characterized by fractures of varying aperture and is the dominant response in all of the borehole data. In this study, we utilize borehole radar data to image fluid-filled fractures outside of the immediate vicinity of the borehole. This is possible due to their strong permittivity contrast with respect to the granitic host rock. In combination with optical televiewer data analysis, the borehole radar image indicates a complicated network of intersecting fractures. Additionally, to shed more light on the characteristics of the system, we use tube wave data from a hydrophone VSP survey and self-potential data. The former is responsive to mechanically compliant and hydraulically transmissive areas, whereas the latter may indicate zones of in- and outflow.

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/content/papers/10.3997/2214-4609.201802588
2018-09-09
2024-04-25
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References

  1. Abrecht, J.
    [1994] Geologic units of the Aar massif and their pre-Alpine rock associations: a critical review: the pre-Alpine crustal evolution of the Aar-, Gotthard- and Tavetsch massifs. Schweizerische mineralogische und petrographische Mitteilungen74(1), 5–27.
    [Google Scholar]
  2. Agemar, T., Weber, J. and Schulz, R.
    [2014] Deep Geothermal Energy Production in Germany. Energies7(7), 4397.
    [Google Scholar]
  3. Bakku, S. K., Fehler, M. and Burns, Daniel
    . [2013] Fracture compliance estimation using borehole tube waves. Geophysics78(4), D249–D260.
    [Google Scholar]
  4. Cheng, Y. and Renner, J.
    [2018] Exploratory use of periodic pumping tests for hydraulic characterization of faults. Geophysical Journal International212(1), 543–565.
    [Google Scholar]
  5. Egli, D., Baumann, R., Küng, S., Berger, A., Baron, L. and Herwegh, M.
    [2018] Structural characteristics, bulk porosity and evolution of an exhumed long-lived hydrothermal reservoir. Tectonophysics in submission.
    [Google Scholar]
  6. Greenwood, A., Caspari, E., Egli, D., Baron, L., Zahner, T., Hunziker, J. and Holliger, K.
    [2018] Characterization and imaging of a hydrothermally active near-vertical fault zone in crystalline rocks based on hydrophone VSP data. Tectonophysics in submission.
    [Google Scholar]
  7. Hofmann, B. A., Helfer, M., Diamond, L. W., Villa, I. M., Frei, R. and Eikenberg, J.
    [2004] Topography-driven hydrothermal breccia mineralization of Pliocene age at Grimsel Pass, Aar massif, Central Swiss Alps. Schweizerische mineralogische und petrographische Mitteilungen84(3), 271–302.
    [Google Scholar]
  8. Wehrens, P., Berger, A., Peters, M., Spillmann, T. and Herwegh, M.
    [2016] Deformation at the frictional-viscous transition: Evidence for cycles of fluid-assisted embrittlement and ductile deformation in the granitoid crust. Tectonophysics693, Part A, 66–84.
    [Google Scholar]
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