<p>EARTHQUAKE SIMULATOR An earthquake simulating machine has a vibrating platform mounted in a frame. The platform is driven by a hydraulic piston which reciprocates the platform through a lever system having a mechanical advantage of about ten to one. The vibration of the platform is isolated from the frame by shock absorbing bushings which support the lever system. Shock absorbing feet may be used to support the frame. The hydraulic piston is controlled by a hydraulic circuit and by an electrical circuit which provides the input to the hydraulic circuit. A feedback circuit monitors the output vibration of the platform</p>
