thatianafernandes / paper-isostatic-grav2d

Non-linear 2D gravity inversion with isostatic constraint

Isostatic constraint for 2D non-linear gravity inversion on rifted margins

by B. Marcela S. Bastos¹ and Vanderlei C. Oliveira Jr.¹

¹Observatório Nacional

This paper is published at Geophysics.

Abstract

We propose a non-linear gravity inversion for simultaneously estimating the basement and Moho geometries, as well as the depth of the reference Moho along a profile crossing a passive rifted margin. To obtain stable solutions, we impose smoothness on basement and Moho, force them to be close to previously estimated depths along the profile and also impose local isostatic equilibrium. Differently from previous methods, we introduce the information of local isostatic equilibrium by imposing smoothness on the lithostatic stress exerted at depth. Our method delimits regions that deviates and those that can be considered in local isostatic equilibrium by varying the weight of the isostatic constraint along the profile. Besides, it allows controlling the degree of equilibrium along the profile, so that the interpreter can obtain a set of candidate models that fit the observed data and exhibit different degrees of isostatic equilibrium. Our method also differs from earlier studies because it attempts to use isostasy for exploring (and not necessarily reducing) the inherent ambiguity of gravity methods. Tests with synthetic data illustrate the effect of our isostatic constraint on the estimated basement and Moho reliefs, specially at regions with pronounced crustal thinning, which are typical of passive volcanic margins. Results obtained by inverting satellite data over the Pelotas basin, an example of passive volcanic margin at the southern of Brazil, agree with previous interpretations obtained independently by combining gravity, magnetic and seismic data available to the petroleum industry. These results show that, combined with a priori information, simple isostatic assumptions can be very useful for interpreting gravity data on passive rifted margins.

Schematic representation of the interpretation model approximating a passive rifted margin

Reproducing the results

You can download a copy of all the files in this repository by cloning the git repository:

git clone https://github.com/pinga-lab/paper-isostatic-grav2D

All source code used to generate the results and figures in the paper are in the code folder. The sources for the manuscript text and figures are in manuscript. See the README.md files in each directory for a full description.

The calculations and figure generation are all run inside Jupyter notebooks. You can view a static (non-executable) version of the notebooks in the nbviewer webservice:

http://nbviewer.jupyter.org/github/pinga-lab/paper-isostatic-grav2D

Running the code

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jupyter notebook

We recommend using a conda environment.

This will start the server and open your default web browser to the Jupyter interface. In the page, go into the code folder and select the notebook that you wish to view/run.

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License

All source code is made available under a BSD 3-clause license. You can freely use and modify the code, without warranty, so long as you provide attribution to the authors. See LICENSE.md for the full license text.

The manuscript text/figures are not open source. The authors reserve the rights to the article content, which is currently published for publication at Geophysics.