Refined mantle velocity model at Ukrainian Shield adjusted after Karato

Abstract

Summary Purpose. The additional velocity boundaries defined from velocity gradients in the upper mantle under Ukraine area need to be validated. These boundaries are outlined at alternation zones of increased and decreased values of the P-wave velocity gradients within tectonic units of Ukrainian Shield. They form characteristic patterns that correlate with main vertical dislocations and boundaries of deep-seated inhomogeneities within mantle. We need to compare them with the known density distributions and derive proper local velocity model based on vp/vs ratio. Method. To prove these boundaries we invert the 1D velocity models taking into account impact of inelasticity in the mantle after Karato (1993) . We compare velocity ratio vp/vs with the known density models as PEM-A, PEM-C, PREM, AK135. The resulting curve was recalculated into a density distribution curve. Results. This procedure reveal a discrepancy between the common models and the estimated model up to a depth of 800 km, while below this depth the coincidence is good. There are outlined 7 structural horizons at upper mantle (under ∼180–190 km, ∼210–220 km, 250–260 km, 360–370 km, 410–420 km, 620–630 km, and ∼660–670 km) and 7 structural horizons at lower mantle (under ∼710–730 km, 760–770 km, 810–820 km, 1050–1060 km, 1660–1710 km, and 1900–1910 km). Practical value. A new approach for the definition of the mantle inhomogeneities distribution based on vp/vs ratio is tested. A radial velocity distribution within mantle from P waves were obtained beneath Ukrainian Shield. It proved the previously identified gradient velocity boundaries within the mantle.