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

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.