HR: 0800h
AN: S51B-0147    [Abstracts]
TI: The Influence of Supercritical H$_{2}$O on Elastic Properties
AU: Ramelow, J
EM: jule@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AU: * Schilling, F R
EM: fsch@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Telegrafenberg, Potsdam, 14473 Germany
AB: Water seems to be an important controlling parameter in active tectonic settings. Especially the concept of earthquake-triggering by "dehydration embrittlement" due to fluid release during dehydration and an increasing pore fluid pressure is discussed intensively. Nonetheless, little is known about their petrophysical signature. To study the influence of fluids on the elastic properties of rocks we performed ultrasonic experiments on encapsulated and non-encapsulated cores of amphibolite and serpentinite. P and S wave velocities are deduced in an internally heated gas-pressure vessel at 900MPa and up to 700$ \deg $C. Without capsule a slight temperature derivative for P-waves (dVp/dT of -0.43 m/(s K) and -0.79 m/( s K) for amphibolite and Serpentinite, respectively) fit quite well with literature data determined and are attributed to the intrinsic elastic properties. Velocities measured on capsulated serpentinite shows a similar behaviour. In contrast, on encapsulated amphibolite we deduce far below dehydration conditions a significant reduction of P-wave derivative of -1.31 m/(s K) with increasing crack density. This can be traced back to water at grain boundaries and an enhanced pore fluid pressure, which affect the sample microstructure exceedingly. Between 400-550$ \deg $C we observe a time-dependent re-increase of velocities, which seems related to a reduction of the pore space as the result of precipitation of minerals along grain boundaries and/ or the expulsion of the fluid phase. Our results show, that already small amounts of water can effect the sample microstructure enormously and thus its elastic properties.
DE: 5112 Microstructure
DE: 5144 Wave attenuation
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting