The article considers the using of the multimodal nonlinear static method as a seismic resistance estimation method of existing turbogenerator foundation structures. The object of research is the turbogenerator foundation on the Tom-Usinsk State District Power Station. The article proposes a modified algorithm for the characteristic point search by the nonlinear static method. According to the calculations results, the existing foundation structures after a partial equipment replacement and the construction site increased seismicity are operational.