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| Titel |
Correlations between electrical and elastic properties of solid-liquid composites with interfacial energy-controlled equilibrium microstructures |
| VerfasserIn |
M. Pervukhina, Y. Kuwahara |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250020428
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| Zusammenfassung |
| Electrical conductivity and seismic velocity are studied for plausible pore geometries in the
Earth’s interior for reliable quantitative analysis of experimental data such as seismic
tomography and magnetotelluric explorations. Electrical conductivity of a two-phase system
with equilibrium, interfacial energy-controlled phase geometry is calculated for the dihedral
angles θ=40o-100o that are typical for rock-aqueous fluid and θ=20o-60o for rock-melt
systems of lower crust and upper mantle for the case of tetrakaidecahedral grains. The
obtained conductivity is demonstrated to be in agreement with the experimentally
measured electrical conductivities of a simple analog material, namely, of open
cell metallic foam. Electrical conductivity vs. seismic velocity correlations are
acquired by combining of the simulated electrical conductivities with the seismic
velocity calculated with the help of equilibrium geometry model Takei (2002) for
the same pore geometries. The results show that electrical conductivity gradually
decreases reaching zero when seismic velocities reach seismic velocities of intact
rock for rock-melt systems, while for rock-aqueous fluid systems with θ-¥60Ë
conductivity drops to zero at velocities up to 10% smaller. This can explain the seeming
discrepancy of the low seismic velocity region, attributed to the high fluid fraction,
and the low electrical conductivity of the same region, which is sometimes faced
at collocated electromagnetic and seismic experiments. The obtained electrical
conductivity – seismic velocity correlations are shown to be practically important for
the distinction between melt and aqueous fluid, for the precise definition of liquid
fraction, and for the discrimination between regions in hydrostatic equilibrium
and those which are subject to strong shear stress or slip process. The analysis
on the basis of the calculated conductivity-velocity correlations of experimental
electrical conductivity and seismic velocity tomography data allowed clarification the
stress state in the region of the deep extension of an active fault. We investigated
the area of the deep extension of the Nagamachi-Rifu by analysis of the data of
collocated magnetotelluric and seismic velocity tomography results in comparison with
the theoretical Ï-V correlations calculated for the equilibrium pore geometry. We
suggested equilibrium stress state with the dihedral angles of 60-80Ë or weakly
non-equilibrium stress state in the region located 0-20km to the northwest of M5.0
earthquake at the depth of 10-17 km and in the region extending 0-40km to the
northwest of M5.0 at the depth of 18-30km on the basis of the analysis. Present
study confirmed the non-equilibrium stress state suggested in the region located
20-40 km to the northwest from the hypocenter of M5.0 earthquake at the depth of
10-17 km. The electrical conductivity and seismic velocities data are shown to
be complementary and be useful to clarify the stress state and specify the liquid
fraction in the regions. The suggested analysis is demonstrated to be practically
important for understanding of stress state in the mid and lower crust and might be
applied to all the high resolution data of collocated electromagnetic and seismic
experiments.
Y. Takei, Effect of pore geometry on Vp/Vs: From equilibrium geometry to crack. J.
Geophys. Res. 107 (2002): 10.1029/2001JB000522. |
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