Abstract
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.
Highlights
The periodic redistribution of ocean mass around the Earth’s surface due to ocean tides deforms the solid Earth, a phenomenon known as ocean tide loading (OTL)
By introducing the detectability ratio for the asthenospheric anelasticity effects and considering the distribution of the available Global Positioning System (GPS) sites, the East China Sea (ECS) region was selected as a potential area to observe the anelastic dispersion in the asthenosphere
In the open sea areas NAO99Jb could be slightly worse than the other ocean tide models, due to the assimilation of more satellite altimetry data in the latter, but this does not outweigh the benefits of forcing the NAO99Jb model to fit a large number of tide gauge observations
Summary
The periodic redistribution of ocean mass around the Earth’s surface due to ocean tides deforms the solid Earth, a phenomenon known as ocean tide loading (OTL). J. Wang et al.: Asthenospheric anelasticity effects around the East China Sea scale spatially coherent differences between GPS-observed and predicted OTL displacements at sites located more than 150 km inland from the coastline and attributed these differences to elastic and inelastic deficiencies in the a priori Earth body tide model. To identify regions where the findings of Bos et al (2015) are testable, we have examined the global distribution of a “detectability ratio” This is defined as the ratio between the elastic–anelastic OTL displacement discrepancy (taken to be the difference between OTL predicted using a purely elastic PREM Green’s function, as described, and that using Bos et al.’s (2015) anelastic S362ANI(M2) Green’s function) as the numerator and the combination of expected GPS observational and ocean tide model related errors as the denominator. We consider the M2 constituent and the vertical component of OTL displacement, as these are dominant in the ECS region
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