Displacement and tilt waveforms at IWTH25. (a) Displacement waveforms on the surface (red) and at the bottom of the borehole (blue) of the IWTH25 station. The origin on the time axis corresponds to the first arrival time of the signal. (b) Temporal variation of the tilt (bottom), its velocity (middle), and its acceleration (top). Tilt motion was computed as the difference between the surface data and borehole data divided by the distance (260 m).