Document Type
Article
Publication Date
8-2025
Publication Title
Earth and Space Science
Abstract
Abstract Following large earthquakes, viscoelastic stress relaxation may contribute to postseismic deformation observed at Earth's surface. Mechanical representations of viscoelastic deformation require a constitutive relationship for the lower crust/upper mantle material where stresses are diffused and, for non‐linear rheologies, knowledge of absolute stress level. Here, we describe a kinematic approach to representing
geodetically observed postseismic motions that does not require an assumed viscoelastic rheology. The core idea is to use observed surface motions to constrain time‐dependent displacement boundary conditions applied at the base of the elastic upper crust by viscoelastic motions in the lower crust/upper mantle, approximating
these displacements as slip on a set of dislocation elements. Using three‐dimensional forward models of viscoelastically modulated postseismic deformation in a thrust fault setting, we show how this approach can accurately represent surface motions and recover predicted displacements at the base of the elastic layer. Applied to the 1999 Chi‐Chi (Taiwan) earthquake, this kinematic approach can reproduce geodetically observed displacements and estimates of the partitioning between correlated postseismic deformation mechanisms. Specifically, we simultaneously estimate afterslip on the earthquake source fault that is similar to previous estimates, along with slip on dislocations at the base of the elastic layer that mimic predictions from viscous
stress dissipation models in which viscosity is inferred to vary three‐dimensionally. A use case for the dislocation approach to modeling viscoelastic deformation is the estimation of spatiotemporally variable fault slip processes, including across sequential interseismic phases of the earthquake cycle, without assuming a
lower crust/upper mantle rheology.
Plain Language Summary: After large earthquakes, Earth's surface can be deformed by relaxation of stress in the lower crust and upper mantle. This postseismic relaxation process is often modeled as viscous flow. Here we present an alternate representation, using displacements at the base of the crust to mimic the stress
change imposed by flow. We compare our displacement‐based approach to models considering viscous flow, finding that our approach can reproduce postseismic motion at Earth's surface. We apply our method to infer mechanisms that may be responsible for observed postseismic deformation following the 1999 Chi‐Chi (Taiwan) earthquake, finding that a combination of displacement at the base of the crust and continued slip on the fault that hosted the earthquake can explain motion measured geodetically at Earth's surface.
DOI
10.1029/2025EA004460
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 International License.
Rights
© 2025 The Authors
Version
Version of Record
Recommended Citation
Loveless, John and Meade, Brendan J., "Kinematic Representations of Viscoelastic Postseismic Deformation" (2025). Geosciences: Faculty Publications, Smith College, Northampton, MA.
https://scholarworks.smith.edu/geo_facpubs/226