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| Titel |
P-wave velocity changes in freezing hard low-porosity rocks: a laboratory-based time-average model |
| VerfasserIn |
D. Draebing, M. Krautblatter |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 6, no. 5 ; Nr. 6, no. 5 (2012-10-22), S.1163-1174 |
| Datensatznummer |
250003794
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| Publikation (Nr.) |
 copernicus.org/tc-6-1163-2012.pdf |
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| Zusammenfassung |
| P-wave refraction seismics is a key method in permafrost research but its
applicability to low-porosity rocks, which constitute alpine rock walls, has
been denied in prior studies. These studies explain p-wave velocity changes in
freezing rocks exclusively due to changing velocities of pore infill,
i.e. water, air and ice. In existing models, no significant velocity increase
is expected for low-porosity bedrock. We postulate, that mixing laws apply
for high-porosity rocks, but freezing in confined space in low-porosity
bedrock also alters physical rock matrix properties. In the laboratory, we
measured p-wave velocities of 22 decimetre-large low-porosity (< 10%)
metamorphic, magmatic and sedimentary rock samples from permafrost sites with
a natural texture (> 100 micro-fissures) from 25 °C to
−15 °C in 0.3 °C increments close to the freezing point.
When freezing, p-wave velocity increases by 11–166% perpendicular to
cleavage/bedding and equivalent to a matrix velocity increase from
11–200% coincident to an anisotropy decrease in most samples. The
expansion of rigid bedrock upon freezing is restricted and ice pressure will
increase matrix velocity and decrease anisotropy while changing velocities of
the pore infill are insignificant. Here, we present a modified Timur's
two-phase-equation implementing changes in matrix velocity dependent on
lithology and demonstrate the general applicability of refraction seismics to
differentiate frozen and unfrozen low-porosity bedrock. |
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