scholarly journals The sensitivity of ocean tide loading displacements to the structure of the upper mantle and crust of Taiwan Island

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Xiaowen You ◽  
Linguo Yuan
Keyword(s):  
Shear Modulus ◽  
Solid Earth ◽  
Upper Mantle ◽  
Vertical Component ◽  
Ocean Tide ◽  
Model Errors ◽  
Ocean Tide Loading ◽  
Taiwan Island ◽  
Ocean Tide Models ◽  
Physical Quantities

AbstractOcean tide loading (OTL) displacements are sensitive to the shallow structure of the solid Earth; hence, the high-resolution spatial pattern of OTL displacement can provide knowledge to constrain the shallow Earth structure, especially in coastal areas. In this study, we investigate the sensitivity of the modeled M2 OTL displacement over Taiwan Island to perturbations of three physical quantities, namely, the density, bulk modulus, and shear modulus in the upper mantle and crust. Then, we compare the sensitivity of the modeled M2 OTL displacement to Earth models with the sensitivity to ocean tide models using root mean square (RMS) differences. We compute the displacement Green’s function and OTL displacement relative to the center of mass of the solid Earth (CE) reference frame, analyze the sensitivity to the three physical quantities in the CRUST1.0 model and the Preliminary Reference Earth Model (PREM), and present their spatial patterns. We find that displacement Green’s functions and OTL displacements are more sensitive to the two elastic moduli than the density in the upper mantle and crust. Moreover, their distinctive sensitivity patterns suggest that the three physical quantities might be constrained independently. The specific relationships between the perturbed structural depths and the distance ranges of peak sensitivities from the observation points to the coastline revealed by the shear modulus can mitigate the nonuniqueness problem in inversion. In particular, the horizontal tidal components observed by the Global Positioning System (GPS) can yield better results in inversions than the vertical component owing to the smaller OTL model errors and the higher structural sensitivity (except for the shear modulus in the asthenosphere).

scholarly journals A comparison of predicted and observed ocean tidal loading in Alaska

2020 ◽  
Vol 223 (1) ◽  
pp. 454-470
Author(s):  
H R Martens ◽  
M Simons
Keyword(s):  
Measurement Error ◽  
Upper Mantle ◽  
Ocean Tide ◽  
Spherically Symmetric ◽  
Surface Displacements ◽  
Tidal Harmonics ◽  
Earth Models ◽  
Ocean Tidal Loading ◽  
Tidal Loading ◽  
Ocean Tide Models

SUMMARY We investigate the elastic and anelastic response of the crust and upper mantle across Alaska to mass loading by ocean tides. GPS-inferred surface displacements recorded by the Plate Boundary Observatory network are compared with predictions of deformation associated with the redistribution of ocean water due to the tides. We process more than 5 yr of GPS data from 131 stations using a kinematic precise point positioning algorithm and estimate tidal contributions using harmonic analysis. We also forward calculate load-induced surface displacements by convolving ocean-tide models with load Green’s functions derived from spherically symmetric Earth models. We make the comparisons for dominant tidal harmonics in three frequency bands: semidiurnal (M2), diurnal (O1) and fortnightly (Mf). Vector differences between predicted and observed ocean tidal loading (OTL) displacements are predominantly sub-mm in magnitude in all three frequency bands and spatial components across the network, with larger residuals of up to several mm in some coastal areas. Accounting for the effects of anelastic dispersion in the upper mantle using estimates of Q from standard Earth models reduces the residuals for the M2 harmonic by an average of 0.1–0.2 mm across the network and by more than 1 mm at some individual stations. For the relatively small Mf tide, the effects of anelastic dispersion (<0.03 mm) are undetectable within current measurement error. Incorporating a local ocean-tide model for the northeastern Pacific Ocean reduces the M2 vertical residuals by an average of 0.2 mm, with improvements of up to 5 mm at some coastal stations. Estimated RMS observational uncertainties in the vertical component for the M2 and O1 tides are approximately ±0.08 mm at the two-sigma level (±0.03 mm in the horizontal components), and ±0.21 mm for the Mf harmonic (±0.07 mm in the horizontal components). For the M2 harmonic, discrepancies between predicted and observed OTL displacements exceed observational uncertainties by about one order of magnitude. None of the ocean tide and Earth model combinations is found to reduce the M2 residuals below the observational uncertainty, and no single forward model provides a best fit to the observed displacements across all tidal harmonics and spatial components. For the O1 harmonic, discrepancies between predicted and observed displacements are generally several-fold larger than the observational uncertainties. For the Mf harmonic, the discrepancies are roughly within a factor of two of the observational uncertainties. We find that discrepancies between predicted and observed OTL displacements can be significantly reduced by removing a network-uniform tidal-harmonic displacement, and that the remaining discrepancies exhibit some regional-scale spatial coherency, particularly for the M2 harmonic. We suggest that the remaining discrepancies for the M2, O1 and Mf tides cannot be fully explained by measurement error and instead convey information about deficiencies in ocean-tide models and deviations from spherically symmetric Earth structure.

scholarly journals Asthenospheric anelasticity effects on ocean tide loading around the East China Sea observed with GPS

Solid Earth ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 185-197 ◽  
Author(s):  
Junjie Wang ◽  
Nigel T. Penna ◽  
Peter J. Clarke ◽  
Machiel S. Bos
Keyword(s):  
East China Sea ◽  
East China ◽  
Ocean Tide ◽  
Earth Model ◽  
Ryukyu Islands ◽  
The East China Sea ◽  
Ocean Tide Loading ◽  
China Sea ◽  
Ocean Tide Models ◽  
Gps Observations

Abstract. Anelasticity may decrease the shear modulus of the asthenosphere by 8 %–10 % at semidiurnal tidal periods compared with the reference 1 s period of seismological Earth models. We show that such anelastic effects are likely to be significant for ocean tide loading displacement at the M2 tidal period around the East China Sea. By comparison with tide gauge observations, we establish that from nine selected ocean tide models (DTU10, EOT11a, FES2014b, GOT4.10c, HAMTIDE11a, NAO99b, NAO99Jb, OSU12, and TPXO9-Atlas), the regional model NAO99Jb is the most accurate in this region and that related errors in the predicted M2 vertical ocean tide loading displacements will be 0.2–0.5 mm. In contrast, GPS observations on the Ryukyu Islands (Japan), with an uncertainty of 0.2–0.3 mm, show 90th-percentile discrepancies of 1.3 mm with respect to ocean tide loading displacements predicted using the purely elastic radial Preliminary Reference Earth Model (PREM). We show that the use of an anelastic PREM-based Earth model reduces these 90th-percentile discrepancies to 0.9 mm. Use of an anelastic radial Earth model consisting of a regional average of the laterally varying S362ANI model reduces the 90th-percentile to 0.7 mm, which is of the same order as the sum of the remaining errors due to uncertainties in the ocean tide model and the GPS observations.

scholarly journals Sea-level fingerprints emergent from GRACE mission data

2019 ◽  
Vol 11 (2) ◽  
pp. 629-646 ◽  
Author(s):  
Surendra Adhikari ◽  
Erik R. Ivins ◽  
Thomas Frederikse ◽  
Felix W. Landerer ◽  
Lambert Caron
Keyword(s):  
Solid Earth ◽  
Sea Level ◽  
Ocean Circulation ◽  
Reference Frames ◽  
Sea Surface ◽  
Ocean Tide ◽  
Mantle Flow ◽  
Systematic Calculation ◽  
Ocean Tide Models ◽  
Grace Mission

Abstract. The Gravity Recovery and Climate Experiment (GRACE) mission data have an important, if not revolutionary, impact on how scientists quantify the water transport on the Earth's surface. The transport phenomena include land hydrology, physical oceanography, atmospheric moisture flux, and global cryospheric mass balance. The mass transport observed by the satellite system also includes solid Earth motions caused by, for example, great subduction zone earthquakes and glacial isostatic adjustment (GIA) processes. When coupled with altimetry, these space gravimetry data provide a powerful framework for studying climate-related changes on decadal timescales, such as ice mass loss and sea-level rise. As the changes in the latter are significant over the past two decades, there is a concomitant self-attraction and loading phenomenon generating ancillary changes in gravity, sea surface, and solid Earth deformation. These generate a finite signal in GRACE and ocean altimetry, and it may often be desirable to isolate and remove them for the purpose of understanding, for example, ocean circulation changes and post-seismic viscoelastic mantle flow, or GIA, occurring beneath the seafloor. Here we perform a systematic calculation of sea-level fingerprints of on-land water mass changes using monthly Release-06 GRACE Level-2 Stokes coefficients for the span April 2002 to August 2016, which result in a set of solutions for the time-varying geoid, sea-surface height, and vertical bedrock motion. We provide both spherical harmonic coefficients and spatial maps of these global field variables and uncertainties therein (https://doi.org/10.7910/DVN/8UC8IR; Adhikari et al., 2019). Solutions are provided for three official GRACE data processing centers, namely the University of Texas Austin's Center for Space Research (CSR), GeoForschungsZentrum Potsdam (GFZ), and Jet Propulsion Laboratory (JPL), with and without rotational feedback included and in both the center-of-mass and center-of-figure reference frames. These data may be applied for either study of the fields themselves or as fundamental filter components for the analysis of ocean-circulation- and earthquake-related fields or for improving ocean tide models.

scholarly journals ANALYSIS OF OCEAN TIDE LOADING ESTIMATED FROM THE GPS COORDINATE TIME SERIES: A CASE STUDY FOR THE BELÉM, BRASÍLIA, EUSÉBIO, MANAUS AND SANTA MARIA STATIONS, BRAZIL

2019 ◽  
Vol 37 (4) ◽  
pp. 565
Author(s):  
Giuliano Sant’Anna Marotta ◽  
Mário Alexandre De Abreu ◽  
Ana Cristina Oliveira Cancoro De Matos ◽  
João Francisco Galera Monico ◽  
George Sand Leão Araújo De França
Keyword(s):  
Solid Earth ◽  
Earth Tide ◽  
Ocean Tide ◽  
Ocean Tide Loading ◽  
Estimated Parameters ◽  
Celestial Bodies ◽  
Tidal Constituents ◽  
Santa Maria ◽  
Solid Earth Tide

ABSTRACT. The Earth suffers deformations due to the gravitational attraction of the celestial bodies and the redistribution of water mass occurring by the action of the ocean tide. These effects are known as solid Earth tide and ocean tide loading, and can be estimated by observations of the amplitudes and phases of their tidal wave constituents. Considering that GNSS observations may be used to estimate these effects and that the solid Earth tide displacement is well resolved, this work estimated and analyzed the amplitudes and phases of the 11 principal constituents of ocean tide loading, using GPS observations. The methodology was applied to data collected from five stations in Brazil, and the amplitudes and phases of the tidal constituents were estimated and evaluated regarding their values and convergence times. The results showed that most of the estimated parameters converged during the analyzed period. In addition, after correcting the effects of ocean tide loading in each GPS solution, using the computed parameters and the existing models, the coordinates were compared and the results presented some local differences, allowing to recommend the use of GPS to estimate tidal constituents considering the local behavior of the point.Keywords: GPS, ocean tide loading, tidal constituents.RESUMO. A Terra sofre deformações devido à atração gravitacional de corpos celestes e também em função da redistribuição de massa d’água que ocorre por ação da maré oceânica. Estes fenômenos são denominados maré terrestre e carga oceânica, e podem ser estimados por meio das amplitudes e fases das componentes de onda de maré. Considerando que as observações GNSS podem ser usadas na estimativa destes efeitos e que os deslocamentos devido à maré terrestre são teoricamente bem resolvidos, este trabalho estimou e analisou as amplitudes e fases das 11 componentes principais de carga oceânica, utilizando observações GPS. A metodologia foi aplicada a dados coletados em cinco estações instaladas no Brasil, e as amplitudes e fases para as componentes de maré foram estimadas e avaliadas, considerando seus valores e tempo de convergência. Os resultados mostraram que a maioria dos parâmetros estimados convergiu durante o período analisado. Além disso, após corrigir os efeitos de carga oceânica em cada solução GPS, utilizando os parâmetros calculados e os modelos existentes, as coordenadas corrigidas foram comparadas e os resultados apresentaram diferenças locais, permitindo recomendar o uso do GPS na estimativa de componentes de maré considerando o comportamento local do ponto.Palavras-chave: GPS, carga oceânica, componentes de maré.

scholarly journals Sea-level fingerprints emergent from GRACE mission data

2019 ◽  
Author(s):  
Surendra Adhikari ◽  
Erik R. Ivins ◽  
Thomas Frederikse ◽  
Felix W. Landerer ◽  
Lambert Caron
Keyword(s):  
Solid Earth ◽  
Sea Level ◽  
Ocean Circulation ◽  
Sea Surface ◽  
Ocean Tide ◽  
Mantle Flow ◽  
Data Set ◽  
Systematic Calculation ◽  
Ocean Tide Models ◽  
Grace Mission

Abstract. The Gravity Recovery and Climate Experiment (GRACE) mission data set has an important, if not revolutionary, impact on how scientists quantify the water transport on the Earth's surface. The transport phenomena include land hydrology, physical oceanography, atmospheric moisture flux, and climate related changes to the cryosphere. The mass transport observed by the satellite system also includes solid Earth motions caused by, for example, great subduction zone earthquakes and glacial isostatic adjustment (GIA) processes. When coupled with altimetry, this space gravimetry data provides a powerful framework for studying climate related changes on interdecadal time scales, such as ice mass loss and sea-level rise. As the changes in the latter are significant over the past two decades, there is a concomitant self-attraction and loading phenomenon generating ancillary changes in gravity, sea surface, and solid Earth deformation. These generate a finite signal in GRACE and ocean altimetry and it may often be desirable to isolate and remove them for the purpose of understanding, for example, ocean circulation changes and post-seismic viscoelastic mantle flow, or GIA, occurring beneath the sea floor. Here we provide a systematic calculation of sea-level fingerprints of continental (water) mass changes using monthly Release-06 GRACE Level-2 Stokes coefficients for the span April 2002 to August 2016 (Adhikari et al., 2019, https://doi.org/10.7910/DVN/8UC8IR), which result in a set of spherical harmonic coefficients for the time-varying geoid, sea surface, and vertical bedrock motion. A simple sum of the spectra yield monthly maps of the desired field and uncertainties therein. These may be applied for either study of the fields themselves or as fundamental filter components for the analysis of ocean circulation and earthquake related fields, or for improving ocean tide models.

scholarly journals OCEAN TIDE LOADING AND RELATIVE GNSS IN THE BRITISH ISLES

Survey Review ◽  
2010 ◽  
Vol 42 (317) ◽  
pp. 212-228
Author(s):  
P. J. Clarke ◽  
N. T. Penna
Keyword(s):  
Ocean Tide ◽  
British Isles ◽  
Ocean Tide Loading
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