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Wet Fault or Dry Fault? A Laboratory Approach to Remotely Monitor the Hydro-Mechanical State of a Discontinuity Using Controlled-Source Seismics
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
2014 (English)In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 171, no 11, 2887-2897 p.Article in journal (Refereed) Published
Abstract [en]

Stress variation and fluid migration occur in deformation zones, which are expected to affect seismic waves reflected off or propagating across such structures. We developed a basic experimental approach to monitor the mechanical coupling with respect to seismic coupling across a single discontinuity between a granite sample in contact with a steel platen. Piezoceramics located on the platen were used to both generate and record the P and S wave fields reflected off the discontinuity at normal incidence. This way, normal (B (n) ) and tangential (B (t) ) compliances were calculated using Schoenberg's linear slip theory (Schoenberg, J Acoust Soc Am 68:1516-1521, 1980) when the roughness, the effective pressure (P (eff), up to 200 MPa), and the nature of the filling (gas or water) vary. We observe that increasing the effective pressure decreases B (n) and B (t) , which is interpreted as the effect of the closure of the voids at the interface, permitting more seismic energy to be transmitted across the interface. Values of B (n) are significantly higher than those of B (t) at low P (eff) (< 60-80 MPa) in dry conditions, and significantly drop under water-saturated conditions. The water filling the voids therefore helps to transmit the seismic energy of compressional waves across the interface. These results show that the assumption B (n) a parts per thousand B (t) commonly found in some theoretical approaches does not always stand. The ratio B (n) /B (t) actually reflects the type of saturating fluids and the effective pressure, in agreement with other experimental studies. However, we illustrate that only the relative variations of this ratio seem to be relevant, not its absolute value as suggested in previous studies. Consequently, the use of B (n) against B (t) plots may allow effective pressure variation and the nature of the pore fluid to be inferred. In this respect, this experimental approach at sample scale helps to pave the way for remotely monitoring in the field the hydro-mechanical state of deformation zones, such as seismogenic faults, fractured reservoirs, or lava conduits.

Place, publisher, year, edition, pages
2014. Vol. 171, no 11, 2887-2897 p.
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Research subject
Geophysics with specialization in Solid Earth Physics
URN: urn:nbn:se:uu:diva-239974DOI: 10.1007/s00024-014-0805-zISI: 000345144300003OAI: oai:DiVA.org:uu-239974DiVA: diva2:775753
Available from: 2015-01-05 Created: 2015-01-05 Last updated: 2015-01-05Bibliographically approved

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