**4. Simulation Shaking-Table Tests**

*4.1. Simulation Shaking Table*

To verify the reliability of the VMD–HHT model and displacement reconstruction method, a series of simulation shaking-table tests were performed using accelerometer in the MIMU. The simulation shaking table (see in Figure 7) comprised a platform framework, steel plates for equipment, two mutually perpendicular screw rods, a servo motor, a control panel, and a power box. The platform frame is 1.2 m long, 1.2 m wide, and 0.5 m high, and the steel plates for equipment are 0.3 m long, 0.1 m wide, and 0.02 m thick. To install the GNSS antenna, a screw hole was drilled through the steel plates; moreover, the screw rods were driven by the servo motor when the steel plates move horizontally with screw rods. In addition, the control system of the shaking table adjusted the vibration amplitude and frequency through the control panel.

**Figure 7.** Shaking table.
