HR: 0800h
AN: G51A-0049    [Abstracts]
TI: Distributed Versus Point Source Models of Volcano Deformation
AU: * Mann, D
EM: doerte@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305 United States
AU: Segall, P
EM: segall@pangea.stanford.edu
AF: Department of Geophysics, Stanford University, Stanford, CA 94305 United States
AB: Volcano deformation is the surface expression of physical processes at depth, including magma accumulation and movement, pressurization, and crystallization. Deformation models are used to extract source parameters including location, depth, and shape of the magma reservoir. Many studies assume simple predefined sources, most commonly a center of dilation or "Mogi" source, which approximates a spherical pressurized cavity in an elastic half-space. Others have employed an approximate solution for a pressurized ellipsoid due to Yang et al [1988]. Some have used more general distributions of centers of dilation, although the physical interpretation of these models is unclear. Eshelby [1957] showed that an appropriate distribution of centers of dilation and vertical double forces yields a uniform pressure on the boundary of an ellipsoid in an elastic full space. Here we explore the possibility of inverting for a distribution of such nuclei of strain that both fit geodetic data and approximately satisfy a uniform pressure boundary condition on a closed surface surrounding the sources. This would allow the data to be interpreted in terms of an internally pressurized cavity of arbitrary shape. We have tested inversions that minimize a data residual norm and regularizing functionals including spatial smoothing and compactness of the source region. We find that the resulting distributions are highly dependent on the modeling constraints chosen, and the spatial distribution of sources and the resulting stress field cannot always be easily interpreted in terms of source geometry. Based on our studies we recommend the following inversion strategy: First invert for a generalized non-isotropic point source, as in Davis [1986]. This provides a reasonable estimate of source parameters including shape (from the strength ratio of vertical and horizontal components of the point source). If the source is located deep relative to its size, a point source will adequately fit the data. If the source is shallow, finite source models approximating an ellipsoidal or sill-like structure can be tested. If simple finite source models fail to fit the data, one can invert for compact distributions about the source. In this case surfaces of constant normal stress around a source region can be used as a boundary condition to allow for non-ellipsoidal geometries.
DE: 8439 Physics and chemistry of magma bodies
DE: 3210 Modeling
DE: 3260 Inverse theory
DE: 1299 General or miscellaneous
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting