The response of visco-elastic crust and mantle to the inflation/deflation of magma chamber

Abstract:

It is important to quantitatively evaluate how magmatic activities at depth are reflected in geodetically (GPS and/or InSAR) observed surface deformation in order to distinguish magma-induced crustal deformation. This study employs 3-D finite element model to examine response of the linear Maxwell visco-elastic crust and mantle to a development of sill. Models with instantaneous and/or time-dependent inflation/deflation of sill at various depths in the crust have predicted geodetically detectable surface deformation, providing important constraints on spatio-temporal-scale of magmatic activities. Instantaneous inflation of sill in the crust causes the surface uplift. The amplitude and wavelength of the uplift are amplified for shallower and deeper inflations, respectively. The inflation occurred over a greater horizontal extent intensify both the amplitude and wavelength. The inflation-induced surface uplift would however abate with time by visco-elastic relaxation. Any signature of sill would disappear in ~ 50 - 100 times Maxwell relaxation time of the crust unless the inflation occurred within the uppermost layer that effectively acts as elastic layer. Time-dependent inflation accompanies with visco-elastic relaxation, and the inflation having occurred over the time-scale of ~ 50 - 100 times crustal relaxation time would provide insignificant signature at the surface, which in turn tells us that crustal deformation would reflect the development of magma chamber only if it has occurred in that time-scale. This study also has found that an ascent of magma into shallower depth may be recognised by an observation such that a horizontal extent over which the surface uplift is progressively intensified focusses into a narrower region.