Abstract: A mechanically fully isolated body (D) is connected by mechanical isolators (C), behaving elastically in all directions, with its basis (B). This basis is linked firmly to the surrounding formation. There exists a frequency range called hole of eigenfrequencies between the highest (6) of the six lowest system eigenfrequencies (1-6)--called fundamental eigenfrequencies--and the lowest (7) of all higher eigenfrequencies (7,8 . . . )--called upper eigenfrequencies--of the oscillatory element consisting of the body (D) and the isolators (C). In this range the oscillatory element presents no eigenfrequencies. The hole of eigenfrequencies shall cover the range of resonance of the relevant design response spectrum of the excitation (E). By these measures the body resists to the strongest earthquakes measured or to be expected at that site.