Software for mapping the effective elastic thickness of the lithosphere

The flexure of elastic plates is a central concept in the theory of plate tectonics, where the Earth's lithosphere (crust and uppermost mantle) reacts to applied loads by bending, a process referred to as flexural isostasy. Estimating the effective elastic thickness (T_e) of the lithosphere (thickness of an equivalent ideal elastic plate) gives important clues on the rheology of the lithosphere and its thermal state. Estimating T_e can be done by modeling the cross-spectral properties (admittance and coherence) between topography and gravity anomaly data, which are proxies for the distribution of flexurally compensated surface and subsurface loads.

This package contains python and fortran modules to calculate the wavelet spectral and cross-spectral quantities of 2D gridded data of topography and gravity anomalies. Once obtained, the wavelet cross-spectral quantities (admittance and coherence) are used to determine the parameters of the effectively elastic plate, such as the effective elastic thickness (T_e), the initial subsurface-to-surface load ratio (F) and optionally the initial phase difference between surface and subsurface loads (alpha). The estimation can be done using non-linear least-squares or probabilistic (i.e., bayesian) inference methods. The analysis can be done using either the Bouguer or Free air gravity anomalies, and over land or ocean areas. Computational workflows are covered in the Jupyter notebooks bundled with this package. The software contains methods to make publication-quality plots using the seaborn package.

Installation, Usage, API documentation and Jupyter Notebooks are described at https://paudetseis.github.io/PlateFlex/

Authors: Pascal Audet (Developer and Maintainer) & Zhezhe Lu (Contributor)

Citing

If you use PlateFlex in your work, please cite the Zenodo DOI.

Contributing

All constructive contributions are welcome, e.g. bug reports, discussions or suggestions for new features. You can either open an issue on GitHub or make a pull request with your proposed changes. Before making a pull request, check if there is a corresponding issue opened and reference it in the pull request. If there isn't one, it is recommended to open one with your rationale for the change. New functionality or significant changes to the code that alter its behavior should come with corresponding tests and documentation. If you are new to contributing, you can open a work-in-progress pull request and have it iteratively reviewed.

Examples of straightforward contributions include notebooks that describe published examples of elastic thickness results. Suggestions for improvements (speed, accuracy, etc.) are also welcome.

References

• Audet, P. (2014). Toward mapping the effective elastic thickness of planetary lithospheres from a spherical wavelet analysis of gravity and topography. Physics of the Earth and Planetary Interiors, 226, 48-82. https://doi.org/10.1016/j.pepi.2013.09.011

• Kalnins, L.M., and Watts, A.B. (2009). Spatial variations in effective elastic thickness in the Western Pacific Ocean and their implications for Mesozoic volcanism. Earth and Planetary Science Letters, 286, 89-100. https://doi.org/10.1016/j.epsl.2009.06.018

• Kirby, J.F., and Swain, C.J. (2009). A reassessment of spectral Te estimation in continental interiors: The case of North America. Journal of Geophysical Research, 114, B08401. https://doi.org/10.1029/2009JB006356

• Kirby, J.F. (2014). Estimation of the effective elastic thickness of the lithosphere using inverse spectral methods: The state of the art. Tectonophysics, 631, 87-116. https://doi.org/10.1016/j.tecto.2014.04.021

Use cases

• Lu, Z., Li, C.-F., Zhu, S., and Audet, P. (2020). Effective elastic thickness over the Chinese mainland and surroundings estimated from a joint inversion of Bouguer admittance and coherence. Physics of the Earth and Planetary Interiors, 301, 106456, https://doi.org/10.1016/j.pepi.2020.106456

• Lu, Z., Audet, P., Li, C.-F., Zhu, S., and Wu, Z. (2021). What Controls Effective Elastic Thickness of the Lithosphere in the Pacific Ocean? Journal of Geophysical Research, https://doi.org/10.1029/2020JB021074