Finite element modeling of surface deformation associated with volcanism

Abstract

Theoretical analyses of observed vertical and horizontal ground surface deformations near active volcanoes, particularly on Kilauea volcano in Hawaii, have led to useful estimates of the location and shape of subsurface magma reservoirs. One of the major shortcomings of the various existing elastic models is that they have very similar near‐field vertical deformations and they do not explain observed differences between vertical and horizontal deformations. Finite element models appear to offer better fits between observed and computed data. Deformations were computed for idealized magma reservoirs of various shapes: spheres, horizontal lenses, vertical plugs, sills, and dikes of various inclinations. The measured surface deformations from the summit magma reservoir of Kilauea can be approximated by a group of vertical plugs whose tops come within 1 km of the surface; surface deformation of the lower east rift zone of Kilauea appears best explained as being produced by increased magma pressure in a 45° south‐dipping dike whose top is about 1 km below the surface.

Time-dependent deformation of Uturuncu volcano, Bolivia, constrained by GPS and InSAR measurements and implications for source models

“…Previous studies have shown that, in a homogeneous medium, prolate sources have u r /u z > 0.5, and oblate sources (sill-like) are characterized by u r /u z < 0.3 (Dieterich and Decker, 1975). For our best-fit model at Uturuncu, the predicted ratio is 0.46-suggesting that surface displacements could either be due to a single prolate source or a dipole.…”

“…Decomposing InSAR line-of-sight (LOS) measurements into three Cartesian displacement vectors can help distinguish between reservoir geometries in the subsurface (e.g., Dieterich and Decker, 1975). The vertical or radial displacement profile alone is insufficient to identify reservoir geometry because the aspect ratio and depth of ellipsoidal sources can be varied such that profiles are indistinguishable (e.g., Fialko et al, 2001).…”

Remarkable cyclic ground deformation monitored in real‐time on Montserrat, and its use in eruption forecasting

“…The source epicenter is constrained by known points of lava effusion and by seismicity. Tilt data from CP2 and CP3 for individual inflations in May, with station radii measured from the assumed epicenter, yield a source depth about 700-800 m. However a cylindrical source is capable of producing similar surface displacement profiles [Dieterich and Decker, 1975], and analysis suggests that the top of the conduit pressure source is perhaps only a few hundred meters below the lava dome. This result provides an explanation for the lack of signals discerned at distant tilt stations.…”

4D volcano gravimetry

“…In volcanology, numerical models have been developed mostly to compute displacements produced by magmatic intrusions into elastic ͑Dietrich and Decker, 1975;Cayol and Cornet, 1998;Williams and Wadge, 2000;Bonaccorso et al, 2005;Lungarini et al, 2005͒ or viscoelastic media ͑Folch et al, 2000Trasatti et al, 2003͒. Most of these studies account for the effect of topography and rheological heterogeneities on deformation.…”