the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
18 Feb 2021
18 Feb 2021
101 Geodynamic modelling: How to design, carry out, and interpret numerical studies
- 1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom
- 2Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Postbox 1028 Blindern, 0315 Oslo, Norway
- 3Department of Earth Sciences, University of Oxford, United Kingdom
- 4Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany
- 5Department of Geological Sciences, University of Florida, USA
- 6Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
- These authors contributed equally to this work.
- 1School of Earth and Environment, University of Leeds, Leeds, LS2 9JT, United Kingdom
- 2Centre for Earth Evolution and Dynamics (CEED), University of Oslo, Postbox 1028 Blindern, 0315 Oslo, Norway
- 3Department of Earth Sciences, University of Oxford, United Kingdom
- 4Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany
- 5Department of Geological Sciences, University of Florida, USA
- 6Department of Earth Sciences, Utrecht University, Utrecht, The Netherlands
- These authors contributed equally to this work.
Abstract. Geodynamic modelling provides a powerful tool to investigate processes in the Earth's crust, mantle, and core that are not directly observable. However, numerical models are inherently subject to the assumptions and simplifications on which they are based. In order to use and review numerical modelling studies appropriately, one needs to be aware of the limitations of geodynamic modelling as well as its advantages. Here, we present a comprehensive, yet concise overview of the geodynamic modelling process applied to the solid Earth, from the choice of governing equations to numerical methods, model setup, model interpretation, and the eventual communication of the model results. We highlight best practices and discuss their implementations including code verification, model validation, internal consistency checks, and software and data management. Thus, with this perspective, we encourage high-quality modelling studies, fair external interpretation, and sensible use of published work. We provide ample examples from lithosphere and mantle dynamics and point out synergies with related fields such as seismology, tectonophysics, geology, mineral physics, and geodesy. We clarify and consolidate terminology across geodynamics and numerical modelling to set a standard for clear communication of modelling studies. All in all, this paper presents the basics of geodynamic modelling for first-time and experienced modellers, collaborators, and reviewers from diverse backgrounds to (re)gain a solid understanding of geodynamic modelling as a whole.
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Iris van Zelst et al.
Status: final response (author comments only)
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CC1: 'Comment on se-2021-14', Paul PUKITE, 20 Feb 2021
Just a comment that will help distinguish this document from what would be generic information that could be applied to any scientific discipline. What geophysics, astrophysics and similar disciplines have in common is the inability to set up a controlled experiment in the lab, which is an important factor in many other disciplines. Nowhere in the document is the lack of experimental control mentioned, which has an impact on how model validation is done. So can't test out a model hypothesis by setting up an experiment in the lab (e.g. no scaling of gravity possible, therefore any tidal forcing models are impossible to do in a lab). What this means is that the concept of cross-validation becomes much more important, in contrast to the typical hypothesis testing and prediction that are the usual yardsticks for evaluating the utility of a model. In addition, can't wait for predictions on geological time-scales that will unfold over the course of years to millenia, but do have historical data that is amenable to cross-validation analysis.
See https://en.wikipedia.org/wiki/Cross-validation_(statistics)
BTW, I come from a solid-state physics background where controlled experiments rule over everything else, and so this gaping hole in the discipline related to geophysics is glaringly obvious. This should be taken as advice from the trenches, no more than that.
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AC1: 'Reply on CC1', Iris van Zelst, 15 Sep 2021
Thanks for this comment. This is indeed a good point and we incorporated it into the manuscript by adding a line to the introduction (l 53-54) and adding a line at the end of Section 6.3 - Testing the model against observations:
“Considering this lack of experimental control from both the real world and analogue models from the lab (see Section 4), techniques such as probability analysis and cross-validation of the models beyond the typical testing and predicting of hypotheses become increasingly important to assess how well models capture the real world.”
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AC1: 'Reply on CC1', Iris van Zelst, 15 Sep 2021
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RC1: 'Comment on se-2021-14', Paul Tackley, 12 May 2021
This is an "educational" paper; it is not presenting new science or techniques, but instead is introducing newcomers to geodynamical modelling. As such, it is very good, and I have only some corrections and suggestions detailed in the attached report.
- AC2: 'Reply on RC1', Iris van Zelst, 15 Sep 2021
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RC2: 'Comment on se-2021-14', Boris Kaus, 01 Jun 2021
This is a lengthy, but well written and useful manuscript that highlights many aspects of geodynamic modelling. I have a number of minor suggestions to further strengthen the manuscriot in the attached pdf.
- AC3: 'Reply on RC2', Iris van Zelst, 15 Sep 2021
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RC3: 'Comment on se-2021-14', Laurent Montesi, 23 Jun 2021
This manuscript serves as a well-designed guide for modeling mantle and crustal-scale processes. As is necessarily the case with an exercise of the sort, it does in place reflect the personal experience and opinions of the authors, but it overall does a very nice job of remaining neutral, and even the more engaged sections are full of important information that will be useful for moving the field forward. I particularly appreciated the discussions of figure accessibility and Section 9 “Software, data, and resource management”. There are also some very important discussions of the objectives of modeling, in particular the difference between “specific” and “generic” modeling. Both are presented as equally valuable, which is an important message to pass to both modeling and non-modeling communities.
Although the paper is already well organized and well written, I do have a few suggestions that could lead to significant rewriting, as detailed in the attached PDF. These include 1) make clearer that the focus of the paper is on geodynamic modeling of the mantle and the crust. 2) emphasize the importance of hypotheses in the model design process. 5) emphasize the role of constitutive relations 6) explain how brittle failure can be implemented. 7) better contrast FEM and FDM. 10) clarify what an “unphysical behavior” is. My biggest concern, though is with section 8.1 “Structure of a geodynamic modelling manuscript” that I find overly prescriptive. Other comments can be seen as minor.
Please note that most of my suggestions can be seen as a matter of personal preference and should not stand in the way of the publication of the paper (even 8.1!). The authors have produced an important manuscript that will many gain a better understanding of geodynamic modeling. That said, there is room in our discipline for personal preferences, and I welcome continued discussion of the topic. More of us should take an occasional pause from the pace of research to reflect on the higher objectives of our work, in this case geodynamic modeling. This paper is a great way to get the conversation started. Thank you for putting it together.
- AC4: 'Reply on RC3', Iris van Zelst, 15 Sep 2021
Iris van Zelst et al.
Iris van Zelst et al.
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