Jerks and conductivity anisotropy of lower mantle

Conductivity anisotropy of the lower mantle presumably caused by phase change of dielectric magnesiowustite at depths of 1500–2000 km is detectable from jerks. Jerks are induced by currents in the fluid outer core, propagate upward from the CMB through anisotropic conducting mantle, and appear on the Earth’s surface. The surface jerk patterns are studied theoretically from the potential of the geomagnetic field presented as a sum of magnetic and electric modes. Equations for the fields of both modes and their relationship in a weakly anisotropic earth are obtained by the perturbation method. The field potential is expanded into a series of spherical harmonics, and the equations are solved in the frequency and time domains. The surface jerk responses can be inverted to retrieve anisotropy parameters; the goal function in the inversion may correspond to misfit between the model and experimental values either along the horizontal or vertical components.