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Observations of ocean tidal load response in South America from subdaily GPS positions

Martens, Hilary R. and Simons, Mark and Owen, Susan and Rivera, Luis (2016) Observations of ocean tidal load response in South America from subdaily GPS positions. Geophysical Journal International, 205 (3). pp. 1637-1664. ISSN 0956-540X. https://resolver.caltech.edu/CaltechAUTHORS:20180710-084415966

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Abstract

We explore Earth's elastic deformation response to ocean tidal loading (OTL) using kinematic Global Positioning System (GPS) observations and forward-modelled predictions across South America. Harmonic coefficients are extracted from up to 14 yr of GPS-inferred receiver locations, which we estimate at 5 min intervals using precise point positioning. We compare the observed OTL-induced surface displacements against predictions derived from spherically symmetric, non-rotating, elastic and isotropic (SNREI) Earth models. We also compare sets of modelled predictions directly for various ocean-tide and Earth-model combinations. The vector differences between predicted displacements computed using separate ocean-tide models reveal uniform-displacement components common to all stations in the South America network. Removal of the network-mean OTL-induced displacements from each site substantially reduces the vector differences between observed and predicted displacements. We focus on the dominant astronomical tidal harmonics from three distinct frequency bands: semidiurnal (M_2), diurnal (O_1) and fortnightly (M_f). In each band, the observed OTL-induced surface displacements strongly resemble the modelled displacement-response patterns, and the residuals agree to about 0.3 mm or better. Even with the submillimetre correspondence between observations and predictions, we detect regional-scale spatial coherency in the final set of residuals, most notably for the M2 harmonic. The spatial coherency appears relatively insensitive to the specific choice of ocean-tide or SNREI-Earth model. Varying the load model or 1-D elastic structure yields predicted OTL-induced displacement differences of order 0.1 mm or less for the network. Furthermore, estimates of the observational uncertainty place the noise level below the magnitude of the residual displacements for most stations, supporting our interpretation that random errors cannot account for the entire misfit. Therefore, the spatially coherent residuals may reveal deficiencies in the a priori SNREI Earth models. In particular, the residuals may indicate sensitivity to regional deviations from standard globally averaged Earth structure due to the presence of the South American craton.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1093/gji/ggw087DOIArticle
ORCID:
AuthorORCID
Simons, Mark0000-0003-1412-6395
Additional Information:© The Authors 2016. Published by Oxford University Press on behalf of The Royal Astronomical Society. Accepted 2016 February 29. Received 2016 February 28; in original form 2015 November 14. Published: 16 March 2016. We are indebted to Duncan Agnew, Richard Ray, Matt King and an anonymous reviewer for insightful ideas and valuable critiques that greatly improved our manuscript. We also sincerely thank Shailen Desai for helpful discussions on OTL analysis and tidal geocentre variations as well as Angelyn Moore and Willy Bertiger for providing ongoing GIPSY support. Dan Bower graciously supplied scripts to extract and plot the seismic tomography data shown in Supporting Information Fig. S5. The GPS data used in our study was made available by the governments of Brazil (Instituto Brasileiro de Geografia e Estatística), Argentina (Instituto Geográfico Nacional), and Uruguay (Servicio Geográphico Militar). We used geographic information from the Scientific Committee on Antarctic Research (SCAR) Antarctic Digital Database (ADD) to develop a land-sea mask around Antarctica. We gratefully acknowledge support from the National Science Foundation Geophysics Program funding under Grant No. EAR-1417245. This manuscript is based upon work supported by the NASA Earth and Space Science Fellowship to HRM under Grant No. NNX14AO04H. Some figures were generated using Generic Mapping Tools (Wessel et al.2013). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-1417245
NASA Earth and Space Science FellowshipNNX14AO04H
NASA/JPL/CaltechUNSPECIFIED
Subject Keywords:Time-series analysis, Satellite geodesy, Tides and planetary waves, South America
Issue or Number:3
Record Number:CaltechAUTHORS:20180710-084415966
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180710-084415966
Official Citation:Hilary R. Martens, Mark Simons, Susan Owen, Luis Rivera; Observations of ocean tidal load response in South America from subdaily GPS positions, Geophysical Journal International, Volume 205, Issue 3, 1 June 2016, Pages 1637–1664, https://doi.org/10.1093/gji/ggw087
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:87683
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:10 Jul 2018 16:05
Last Modified:03 Oct 2019 19:58

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