Anelasticity and Lateral Heterogeneities in Earth's Upper Mantle: Impact on Surface Displacements, Self‐Attraction and Loading, and Ocean Tide Dynamics

Pingping Huang,Maik Thomas,Roman Lucas Sulzbach,Henryk Dobslaw,Volker Klemann,Zdeněk Martinec,Yoshiyuki Tanaka

doi:10.1029/2021jb022332

Abstract

AbstractSurface displacement and self‐attraction and loading (SAL) elevation induced by ocean tides are known to be affected by material properties of the solid Earth. Recent studies have shown that, in addition to elasticity, anelasticity considerably impacts surface displacements due to ocean tide loading (OTL). We employ consistent 3D seismic elastic and attenuation tomography models to construct 3D elastic and anelastic earth models, and derive corresponding averaged 1D elastic/anelastic models. We apply these models to systematically study the impact of anelasticity and lateral heterogeneity on M2 OTL displacements and SAL elevation. We find that neglecting lateral heterogeneities highly underestimates displacements and SAL elevation in mid‐ocean‐ridge regions and in some coastal areas of North and Central America. In comparison to PREM, 3D anelastic models can increase the predicted amplitudes of the vertical displacement and SAL elevation by up to 1.5 mm. The increased amplitudes reduce the discrepancy between GPS‐observed OTL displacements and their predictions based on PREM in places like Cornwall (England), Brittany (France), and the Ryukyu Islands (Japan). Applying our results to ocean tides, we discover that the impact on ocean tide dynamics exceeds the predicted SAL elevation correction with an RMS of about 1 mm, reaching an RMS of more than 5 mm in areas like North Atlantic or East Pacific. Due to the fact that such a value reaches the accuracy of modern data‐constrained tidal models, we regard the impact of anelastic shear relaxation as significant in tidal modeling.

Highlights

Ocean tide loading refers to the periodic redistribution of water masses due to tidal forcing, which causes deformations of the solid Earth and perturbations of the gravity field
In calculating the dispersion of shear modulus from the seismic to M2 tide frequency, we considered two values of α, that is, 0.00 and 0.25 that are typically used in literature (e.g., Benjamin et al, 2006; Bos et al, 2015)
We found that, compared to PREM, the 1D anelastic models experience a high reduction of shear modulus in the high-attenuation zone

Summary

Introduction

Ocean tide loading refers to the periodic redistribution of water masses due to tidal forcing, which causes deformations of the solid Earth and perturbations of the gravity field. The resulting elastic and gravitational responses of the solid Earth are termed “load tides” (e.g., Farrell, 1972). Load tides at the Earth's surface can be described as vertical displacement, horizontal displacement and the gravitational potential increment. Load tides are as important as body tides (e.g., Takeuchi, 1950) in making up the total tide of the solid Earth induced by the astronomical forces. The SAL potential (SAL elevation times surface gravity) induces secondary barotropic accelerations that influence ocean tide dynamics, and, as a result, their consideration is a necessity for generating an accurate ocean

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