Composition and material properties of magma chambers from effective medium theory

M. A. J. Taylor and S. C. Singh

Bullard Laboratories, Department of Earth Sciences, University of Cambridge, Cambridge, CB3 0EZ, U.K.

IUGG Meeting, Birmingham, 1999

 
The quantification of melt properties within a magma reservoir is extremely important in predicting and monitoring of volcanic eruptions.  The comparatively low rigidity of magma chambers beneath volcanoes and mid-ocean ridges results in a low-velocity zone.  Seismic tomography can provide us information about the wave velocities, and also attenuation and anisotropy of these regions.  Here we use effective medium theory to relate this information to, and place subsequent constraints on, the material properties and composition of such magmatic bodies.

Using a combination of the self consistent scheme [Hill, J. Mech. Phys. Solids, 1965, Budiansky, J. Mech. Phys. Solids, 1965] and differential effective medium theory [Boucher, Rev. Metall., 1976 and McLaughlin, Int. J. Eng. Sci., 1977] in a similar way to Mainprice [Tectonophys, 1997] we examine the effect of introducing inclusions of melt into a solid matrix on the elastic constants (and hence shear and compressional velocities), attenuation, and anisotropy of the resulting medium.  We consider both a homogeneous distribution of spherical inclusions and either aligned or randomly oriented elliptical inclusions.  The effect of assuming an isotropic or anisotropic background matrix material is also considered.  From this we are able to place some bound on the melt fraction and possible microstructure of magma chambers that is consistent with parameters from seismic inversions.  In particular we hope to apply this technique to the data from the 1996 and 1997 land and sea reflection surveys at Mount Vesuvius [Gasparini, EOS, 1998].
 



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