Yurii Dubovenko
Advanced technique for the investigation of the deep structure of the upper mantle structures derived from analysis of P-waves velocity gradients curves compared to standard PREM model with adjusted after Karato core-mantle boundary is developed. Our approach to define the mantle boundaries is based on the calculations of the sequence of P-waves velocity derivatives (1st, 2nd, and gradient). We obtain new set of velocity gradient distributions along the principal tectonic units of the Ukrainian Shield between two long composite profiles. The boundaries of the mantle discontinuities according to the velocity gradient distribution we define through a special manner to eliminate the false anomalies and the fluctuations of the velocity curves that occur due to the conversion of the hodograph into the mean velocities. The smoothing of the velocity curve we perform with a previously defined wavelength step of 50 km. We treat the calculated velocity gradient anomalies as the useful response above the appropriate deep layers, which have different velocity accelerations levels inside the upper mantle. We assume that the mantle anomalies have the same physical parameters (i.e. density/viscosity distributions, temperature gradients etc.) within each range of the equal acceleration value. The singular points determined by the inflections of the gradient curve could be the possible boundaries of additional inhomogeneities within the mantle. The 2.5-D model of the 1-th and 2-th gradient curves (the acceleration of the P-waves velocity gradients) determine the position of the max / min anomalies of these gradients at the seismic profiles within Ukrainian Shield. The distribution of velocity gradients of P-waves within the upper mantle in the depth range of 50–750 km reveals a series of new gradient velocity boundaries within 3 principal structural horizons of the upper mantle (under ~ 200–300 km, ~ 410–500 km, and ~ 600–650 km respectively). Now we try verifying this technique on another tectonic sites.
When verified, this technique proves the new instrument for accurate identification of mantle thresholds beneath principal tectonic units of the world and provides the opportunity to maintain thin features of mantle physics, thus contributing to our understanding of the nature of Earth's interiors.
I've got a dream to unite the best detailed synthesized velocity gradient profiles through the Europe and Asia transects to provide a refined composite structure of the mantle under the continent area.
Institute of Geophysics by S.I. Subbotin name NAS of Ukraine
We analyze the basic techniques for the investigation of the deep structure of the mantle derived from the velocity field by means of analytical transformants.
The layout of possible mantle irregularities with min (blue) and max (red) anomalies of P-waves velocity gradients and the layout of in-depth distribution ...
