The Seismic Signature of Pressure Driven Flow in the Earth's Asthenosphere

Recent geodynamic studies have suggested that asthenosphere flow is driven by a combination of plate drag from above and by lateral pressure gradients within the mantle below plates. Determining how the component of hypothesized pressure driven flow links to observations is critical to testing this idea. We explore a link by producing synthetic seismics from mantle flow models and comparing those predictions with published observations of seismic anisotropy in the upper mantle. Our intent is twofold, to ground-truth mantle dynamics models and to connect seismic anisotropy observations to plate driving forces. We present initial model-to-data comparisons for the end-member cases of plate-driven Couette flow and pressure-driven plug flow in the asthenosphere. Couette flow generates an asthenosphere flow profile that linearly decreases with depth, producing constant shearing throughout the asthenosphere. Plug flow produces an asthenosphere flow profile with a near constant velocity central region bounded above and below by concentrated shear layers. We determine the seismic signature of each end-member. For the more likely case that both components are operative, we test the degree to which the strength of each component can be distinguished using existing seismic anisotropy observations. If each component is distinguishable, then local plate driving forces (slab-pull vs asthenosphere-drag) can be determined by examining seismic anisotropy variations with depth.