@article{ecf0cc648b104c5da357ccdd25475762,
title = "The Sensitivity of Joint Inversions of Seismic and Geodynamic Data to Mantle Viscosity",
abstract = "Seismic tomography has revealed the existence of large-scale velocity heterogeneities in the mantle. The interpretation of seismic velocity anomalies in terms of temperature and chemical composition is nonunique. We use geodynamic observations including gravity, plate motions, dynamic topography, and excess ellipticity of the core-mantle boundary combined with seismic observations to investigate the thermo-chemical structure of the mantle through joint inversions. An outstanding issue, however, is the physical connection between mantle density anomalies and the surface geodynamic observations, which requires knowledge of the mantle viscosity structure. Here we perform joint inversions assuming different viscosity profiles and examine the dependence of the results on the viscosity. We first assume that mantle heterogeneity is due to thermal variations, which places a constraint on the relation between seismic velocity and density, and we subsequently relax the constraint to allow for potential nonthermal effects. In all of our joint inversions, a nonthermal origin of density anomalies is required to explain the geodynamic data, though the amount varies with the assumed viscosity structure. A common observation is a high-density chemical signal in the center of the large low-shear-velocity provinces at the base of the mantle resulting in a near neutral or slightly dense overall buoyancy there. Using the derived density models and their corresponding viscosity profiles, we also calculate instantaneous mantle flow fields. The predicted flow fields derived from joint inversions are generally similar but are quite different from flow fields using density models derived from a posteriori scaling of pure seismic tomography models.",
keywords = "Joint Inversion, LLSVP, Mantle Density Anomaly, Mantle Flow, Mantle Viscosity, Seismic Tomography",
author = "Chang Lu and Forte, {Alessandro M.} and Simmons, {Nathan A.} and Grand, {Stephen P.} and Kajan, {Marie N.} and Hongyu Lai and Garnero, {Edward J.}",
note = "Funding Information: We thank Incorporated Research Institutions for Seismology, Data Management Center (IRIS DMC, https://ds.iris.edu/ds/nodes/dmc/), Observations & Research Facilities for European Seismology (ORFEUS, https://www.orfeus-eu.org/), Northern California Earthquake Data Center (NECDC, http://ncedc.org/), F-net Broadband Seismograph Network (F-net, http://www.fnet.bosai.go.jp/), and Canadian National Seismic Network (CNSN, http://www.earthquakescanada.nrcan.gc.ca/stndon/CNDC/) for providing data used in this study. We also thank Jung-Fu Lin, Thorsten Becker, Suyu Fu, Petar Gli{\v s}ovi{\'c}, and Paul Bremner for valuable discussions. This research was supported by NSF Grant EAR-1648770 as well as by the Jackson School of Geosciences at the University of Texas at Austin. A. M. F. acknowledges support of this work provided by NSF Grant EAR-1903108 as well as by the University of Florida. E. J. G. acknowledges support provided by NSF Grant EAR-1648817. Funding Information: We thank Incorporated Research Institutions for Seismology, Data Management Center (IRIS DMC, https://ds.iris.edu/ds/nodes/dmc/ ), Observations & Research Facilities for European Seismology (ORFEUS, https://www.orfeus‐eu.org/ ), Northern California Earthquake Data Center (NECDC, http://ncedc.org/ ), F‐net Broadband Seismograph Network (F‐net, http://www.fnet.bosai.go.jp/ ), and Canadian National Seismic Network (CNSN, http://www.earthquakescanada.nrcan.gc.ca/stndon/CNDC/ ) for providing data used in this study. We also thank Jung‐Fu Lin, Thorsten Becker, Suyu Fu, Petar Gli{\v s}ovi{\'c}, and Paul Bremner for valuable discussions. This research was supported by NSF Grant EAR‐1648770 as well as by the Jackson School of Geosciences at the University of Texas at Austin. A. M. F. acknowledges support of this work provided by NSF Grant EAR‐1903108 as well as by the University of Florida. E. J. G. acknowledges support provided by NSF Grant EAR‐1648817. Publisher Copyright: {\textcopyright}2020. American Geophysical Union. All Rights Reserved.",
year = "2020",
month = apr,
day = "1",
doi = "10.1029/2019GC008648",
language = "English (US)",
volume = "21",
journal = "Geochemistry, Geophysics, Geosystems",
issn = "1525-2027",
publisher = "American Geophysical Union",
number = "4",
}