Asthenospheric anelasticity effects on ocean tide loading around the East China Sea observed with GPS
2020
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.
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