HR: 0800h
AN: G51A-0050    [Abstracts]
TI: Magma Intrusion Estimated From InSAR Data: Sensitivities to Homogeneous, Isotropic, Poisson-solid, and Half-space Assumptions
AU: * Masterlark, T
EM: masterlark@usgs.gov
AF: USGS/EROS Data Center, 47914 252nd Street, Sioux Falls, SD 57005 United States
AB: Simple elastic models that simulate deformation caused by magma intrusion within a volcano are readily available and often take the form of an expansion source embedded in a homogeneous, isotropic, Poisson-solid half-space (HIPSHS). These models are commonly used in inverse methods to precisely estimate deformation source parameters from deformation data. The accuracy of these estimated deformation source parameters depends on the validity of the HIPSHS assumptions. Generally, the HIPSHS assumptions poorly represent an actual volcano. Interferometric synthetic aperture radar (InSAR) data reveal that Okmok volcano, Alaska, deflated more than a meter due to lava extrusion during the 1997 eruption of the volcano. Using InSAR-observed deformation of Okmok volcano as an example, deformation prediction sensitivities to the HIPSHS assumptions are identified via forward and inverse modeling methods. Green's functions for displacement due to an expansion source at depth are computed using a combination of analytical and finite element models that systematically relax the requirements for HIPSHS assumptions. Comparisons among the results obtained using HIPSHS versus non-HIPSHS models identify the prediction sensitivity to each of the HIPSHS assumptions. Prediction sensitivity to topographic effects is relatively subtle. Forward modeling indicates prediction sensitivities associated with each of the isotropic, Poisson-solid, and homogeneous assumptions (listed in the order of increasing severity) have magnitudes as large as several tens of centimeters. Deformation source parameters, estimated using inverse models, are particularly sensitive to lateral variations of material properties associated with a caldera. Quantitative interpretations of volcano deformation source parameters, inverted from deformation data, require careful assessments of the deformation models at the core of the inverse methods.
DE: 8434 Magma migration
DE: 6924 Interferometry
DE: 3230 Numerical solutions
DE: 3260 Inverse theory
DE: 1213 Earth's interior--dynamics (8115, 8120)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting