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A Bayesian 3-D linear gravity inversion for complex density distributions: application to the Puysegur subduction system

Hightower, Erin and Gurnis, Michael and Van Avendonk, Harm (2020) A Bayesian 3-D linear gravity inversion for complex density distributions: application to the Puysegur subduction system. Geophysical Journal International, 223 (3). pp. 1899-1918. ISSN 0956-540X. https://resolver.caltech.edu/CaltechAUTHORS:20201103-150735045

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Abstract

We have developed a linear 3-D gravity inversion method capable of modelling complex geological regions such as subduction margins. Our procedure inverts satellite gravity to determine the best-fitting differential densities of spatially discretized subsurface prisms in a least-squares sense. We use a Bayesian approach to incorporate both data error and prior constraints based on seismic reflection and refraction data. Based on these data, Gaussian priors are applied to the appropriate model parameters as absolute equality constraints. To stabilize the inversion and provide relative equality constraints on the parameters, we utilize a combination of first and second order Tikhonov regularization, which enforces smoothness in the horizontal direction between seismically constrained regions, while allowing for sharper contacts in the vertical. We apply this method to the nascent Puysegur Trench, south of New Zealand, where oceanic lithosphere of the Australian Plate has underthrust Puysegur Ridge and Solander Basin on the Pacific Plate since the Miocene. These models provide insight into the density contrasts, Moho depth, and crustal thickness in the region. The final model has a mean standard deviation on the model parameters of about 17 kg m⁻³, and a mean absolute error on the predicted gravity of about 3.9 mGal, demonstrating the success of this method for even complex density distributions like those present at subduction zones. The posterior density distribution versus seismic velocity is diagnostic of compositional and structural changes and shows a thin sliver of oceanic crust emplaced between the nascent thrust and the strike slip Puysegur Fault. However, the northern end of the Puysegur Ridge, at the Snares Zone, is predominantly buoyant continental crust, despite its subsidence with respect to the rest of the ridge. These features highlight the mechanical changes unfolding during subduction initiation.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1093/gji/ggaa425DOIArticle
https://ngdc.noaa.gov/mgg/sedthickRelated ItemData
https://topex.ucsd.edu/marine_grav/mar_grav.htmlRelated ItemData
https://niwa.co.nz/our-science/oceans/bathymetryRelated ItemData
http://www.marine-geo.org/collections/#!/collection/Seismic#summaryRelated ItemData
ORCID:
AuthorORCID
Hightower, Erin0000-0002-4734-5159
Gurnis, Michael0000-0003-1704-597X
Additional Information:© The Author(s) 2020. Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2020 September 4. Received 2020 September 4; in original form 2020 May 30. Published: 08 September 2020. Supported by the National Science Foundation through awards OCE-1654766 (to Caltech) and OCE-1654689 (to UT Austin). This material is based upon work supported by the National Science Foundation Graduate Research Fellowship Program under Grant No. DGE-1745301. We thank IHS-Markit for a university educational license for Kingdom Software, provided to Caltech, for seismic data visualization and interpretation. We thank Kim Welford, Scott King and Sean Gulick for their helpful and insightful comments on the manuscript and Rupert Sutherland, Brandon Shuck and Joann Stock for helpful discussion. Data Availability: https://ngdc.noaa.gov/mgg/sedthick/. Gravity data used in the inversion, Sandwell et al. (2019) global 1 min marine gravity grid, are publicly available from the Scripps Institute of Oceanography at https://topex.ucsd.edu/marine_grav/mar_grav.html. Bathymetric data used in the inversion (Mitchell et al. 2012) is publicly available from the New Zealand Institute for Water and Atmospheric Research (NIWA) at https://niwa.co.nz/our-science/oceans/bathymetry. Seismic data from the SISIE cruise, MGL1803, is available at the Lamont-Doherty Earth Observatory, Marine Geoscience Data System (MGDS), Academic Seismic Portal: http://www.marine-geo.org/collections/#!/collection/Seismic#summary. Sediment thickness data use to constrain the inversion (Straume et al. 2019) are publicly available from NOAA at https://ngdc.noaa.gov/mgg/sedthick/. The gravity inversion code will be available on CaltechDATA (https://data.caltech.edu/) and GitHub, and per communication with the corresponding author.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFOCE-1654766
NSFOCE-1654689
NSF Graduate Research FellowshipDGE-1745301
Subject Keywords:Gravity anomalies and Earth structure, New Zealand, Inverse theory, Statistical methods, Subduction zone processes
Issue or Number:3
Record Number:CaltechAUTHORS:20201103-150735045
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20201103-150735045
Official Citation:Erin Hightower, Michael Gurnis, Harm Van Avendonk, A Bayesian 3-D linear gravity inversion for complex density distributions: application to the Puysegur subduction system, Geophysical Journal International, Volume 223, Issue 3, December 2020, Pages 1899–1918, https://doi.org/10.1093/gji/ggaa425
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:106409
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:04 Nov 2020 17:10
Last Modified:30 Jan 2021 00:42

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