We studied the isotropic ball using data of Preliminary Reference Earth Model (PREM). It is shown that such a ball should be either destructed or gone into a more stable equilibrium state with uneven distributed deformation under thermobaric condition of the inner core. Body elastic waves with real velocities cannot propagate in it. This manuscript is devoted to study the situation from the standpoint of nonlinear geomechanics. A number of necessary principles of Mechanics of Deformable Solid Body (MDSB) is given at the beginning of the analysis. A brief review of the published latest experimental work is performed. It is established that proper attention to the role of the MDSB principles in micro‐scale (nano) experiments of the physical level has not been given. Deformation properties of solid bodies are emphasized in microscale and macroscale. Application of linear acoustoelasticity and extrapolation of Birch's linear law of the inner core and use of an idea on variability of elasticity moduli with the increase of pressure and temperature have contributed to obtained pseudo data for the geological medium of the Earth's core instead of linear data on the physicomechanical properties. It is proposed that parallel to elimination of the indicated disadvantages, collection, processing and interpretation should be performed using nonclassically linearized approach. This set of necessary actions is offered as the “key” of geomechanical analysis. The proper application will allow conducting similar analysis concerning other solid‐state structures of the Earth. Plain Language Summary According to theoretical models of the internal structure and geodynamic development of the Earth, a solid sphere with a radius of 1,250 km formed ~1.5–3 billion years ago. Recent studies show that such a sphere with the parameters accepted in the etalon models should deform and lose its spherical shape under the existing thermobaric conditions. In this sphere, elastic waves cannot propagate at the true velocity. These problems are discussed in this manuscript. It is indicated that current situation can be related to insufficient attention to geomechanical aspects while processing and interpretation of initial data, incorrect imagination on change of thermobaric condition of elastic physicomechanical parameters and Birch's linear diagram extrapolation on thermobaric condition of the core. As a result, pseudo data have been collected instead of data of linear physical and mechanical properties for solid core. A new method of geomechanical analysis is proposed to clarify this problem based on deformed solid body mechanics including fundamental principles of nonclassically linearized elastodynamics.
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