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Probing Asthenospheric Density, Temperature, and Elastic Moduli Below the Western United States
- Ito, Takeo, Simons, Mark
- Science 2011 v.332 no.6032 pp. 947-951
- geodesy, models, modulus of elasticity, temperature, tides, Western United States
- Periodic ocean tides continually provide a cyclic load on Earth's surface, the response to which can be exploited to provide new insights into Earth's interior structure. We used geodetic observations of surface displacements induced by ocean tidal loads to constrain a depth-dependent model for the crust and uppermost mantle that provides independent estimates of density and elastic moduli below the western United States and nearby offshore regions. Our observations require strong gradients in both density and elastic shear moduli at the top and bottom of the asthenosphere but no discrete structural discontinuity at a depth of 220 kilometers. The model indicates that the asthenosphere has a low-density anomaly of approximately 50 kilograms per cubic meter; a temperature anomaly of approximately 300°C can simultaneously explain this density anomaly and inferred colocated minima in elastic moduli.