论文和技术资料

Numerous volcanic systems across the world are actively undergoing unrest, resulting in non-eruptive episodes of inflation and deflation. Whilst these episodes of ground deformation are readily identifiable within geodetic time-series e.g. GPS, InSAR, the underlying processes facilitating this deformation are more enigmatic. By modeling these observed ground deformation signals, the ultimate aim is to infer characteristics of the deforming source; namely the size and time-dependent evolution of the system and, potentially, the fluxes of magma involved. Traditionally, these parameters are estimated analytically using simple elastic models. However, inelastic rheological effects are increasingly utilized to account for the elevated crustal temperatures and thermal regimes typically induced by long-lived magmatic systems, where a component of viscous behavior is more likely to characterize the observed deformation field. Numerical models allow a given volcanic system to be better represented, through the inclusion of topography and heterogeneous mechanical and thermal properties. Spatially-variable crustal properties within a viscoelastic regime result in partitioning of the deformation field; and can significantly alter the inferred reservoir evolution, driving an episode of unrest, when compared to simpler homogeneous models.

With ground deformation studies incorporating viscoelastic regimes becoming more commonplace, we present comparisons of the Maxwell and Standard Linear Solid viscoelastic configurations, and their associated constitutive behaviors, in response to distinct reservoir evolutions. We utilize the Structural Mechanics and Heat Transfer modules within the COMSOL Multiphysics^® simulation software to construct ground deformation models of the Lake Taupo region in New Zealand, incorporating heterogeneous mechanical properties, from seismic tomography data, and a temperature-dependent viscosity distribution. We also investigate the differences between pressurization (stress-based) and volume change (strain-based) deformation modes in viscoelastic media; two contrasting approaches that are assumed to result in equivalent deformation through elastic modeling. Our results illustrate that the perceived influence of viscoelasticity is dependent on the mode of deformation, with stress-based pressurization models imparting enhanced deformation relative to the elastic models, a result of creep behavior, whereas strain-based volumetric models exhibit reduced levels of deformation, due to the relaxation of crustal stresses. We demonstrate that, whilst the inferred source evolution from classical elastic deformation models directly reflect the profile of a deformation time-series, time-dependent viscoelastic behaviors can produce deformation time-series that deviate significantly from the profile of the modeled reservoir evolution. Consequently, we establish that the characterization of an unrest episode is critically dependent on the rheology utilized in the deformation model.