Published December 2025 | Published
Journal Article Open

Limits on inferring an effective lithospheric rheology from geodetic observations of the earthquake cycle

  • 1. ROR icon Jet Propulsion Lab
  • 2. ROR icon California Institute of Technology

Abstract

The relationship between stress and deformation of the solid Earth at various temporal and spatial scales can be described using a variety of constitutive relations. Although our knowledge of the elastic component of these constitutive relations is relatively well-constrained by seismological observations, there are limited opportunities to probe the inelastic component of plausible constitutive relations. Focusing on viscoelastic rheologies, the exact formulation of the viscous component of the rheology of the crust–mantle system is not uniquely constrained, i.e. multiple formulations (linear Burgers and power-law) are able to recreate geodetic observations of the earthquake cycle. Here, we show that it is possible to discriminate between these commonly adopted rheological models under certain conditions, even with the limited observational time span of geodetic networks. We first run a set of numerical simulations of periodic earthquake cycles as well as 2-event sequences for a two-dimensional strike–slip plate boundary, assuming a 20-km-thick frictional fault in an elastic layer overlying a 30-km-thick viscoelastic channel, to predict the resulting surface displacement time series over a 20-year time window. We use a rate-dependent friction law for the fault and a combined diffusion and dislocation creep viscous flow law with laboratory-derived rheological parameters to describe the non-elastic properties of the medium. We invert the synthetic surface displacements to obtain best-fit parameters for a simplified boundary element representation of each rheological model, assuming all viscous strain is localized beneath the fault, and compare the misfits. Linear Burgers and power-law rheologies are nearly indistinguishable when considering periodic events, but they can be distinguished using data from earthquake sequences when events are sufficiently different in magnitude (at least 0.2 units in magnitude) and occur with adequate temporal separation (∼ 1–10 years). However, when the true parameters represent a power-law rheology, it is not possible to uniquely recover all the rheological parameters.

Copyright and License

© The Author(s) 2025. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

Acknowledgement

The authors thank the Editor Youichiro Takada and two anonymous reviewers for their feedback on this manuscript. RM was partly supported by a Texaco Postdoctoral Fellowship at Caltech and the NASA Postdoctoral Program administered by Oak Ridge Associated Universities under contract with NASA. A portion of the research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). © 2025. All rights reserved.

Data Availability

MATLAB code required to run these simulations is available at https://github.com/mallickrishg/viscofric2d_evo.

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Additional details

Created:
May 26, 2025
Modified:
May 26, 2025