Inference of Mass Anomalies in Planetary Interiors Using a Bayesian Global Gravity Field Inversion
Inference of Mass Anomalies in Planetary Interiors Using a Bayesian Global Gravity Field Inversion
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Date
2020
Authors
Izquierdo Gonzalez, Kristel Del Carmen
Advisor
Montesi, Laurent G. J.
Lekic, Vedran
Lekic, Vedran
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DRUM DOI
Abstract
Knowledge about the interior density distribution of a planetary body can constraingeophysical processes and reveal information about the origin and evolution
of the body. Properties of this interior distribution can be inferred by analyzing
gravity acceleration data sampled by orbiting satellites. Usually, the gravity data is
complemented with additional laser ranging or seismic data in order to reduce the
range of possible density models of the interior. However, additional data might not
be available and tight prior constraints on model parameters might not be justified.
In this case, the flexibility of using non-informative priors and the ability to quantify
the non-uniqueness of the gravity inversions are of even greater importance.
In this work, we present a gravity inversion algorithm, THeBOOGIe, thatsamples the posterior distribution of density in the interior of a planet or moon
according to Bayes theorem, following a Metropolis-Hastings iterative algorithm. It
uses non-informative priors on the number, location, shape and magnitude of density
anomalies. Different samples of the posterior show different density models of the interior
consistent with the observed gravity data. Inversions of synthetic gravity data
are ran using point masses, spherical caps and Voronoi regions (VRs) to parametrize
density anomalies. THeBOOGIe is able to retrieve the lateral location of shallow
density anomalies and the shape, depth and magnitude of a mid-mantle anomaly.
The uncertainty of the model parameters increases with depth, as expected.
Bouguer gravity data of the Moon obtained by the GRAIL mission was invertedusing a VR parametrization. Shallow anomalies related to the SPA basin,
crustal dichotomy and near side basins were found in the correct latitude and longitude
and a trade-off in their thickness and magnitude. Positive and negative
density anomalies were found in the depth range 500-1141 km. The location of deep
moonquakes do not have a clear relation to the location of these density anomalies.