Abstract: The near-fault ground motion has long been ignored in the seismic design phase of the underground caverns. Hence this issue needs to be seriously addressed. The differences between near-fault and far-field ground motions are firstly discussed, along with the impact of the respective ground motion on underground caverns. Then a modified simulation method of near-fault pulse-type ground motion is proposed. And with the simulated ground motion, the seismic stability of underground caverns for a hydropower station is studied. The results indicate that compared with the conventional far-field ground motion, the near-fault ground motion is characterized by greater Vmax /Amax and Dmax /Amax values (where Vmax, Dmax, Amax are peak values of velocity, displacement and acceleration). And energy of near-fault ground motion is concentrated in 0~1 Hz band. The damage caused by near-fault is far more serious than that of by far-field ground motion, even with same amplitude and spectrum. The proposed simulation method is well logical for considering the information carried in the [1/Tp, 1] Hz. With current calculation conditions, the underground powerhouse is in a potential danger of failure under the near-fault ground motion. Thus further specific risk assessment for near-fault ground motions is expected to check if specialized seismic reinforcement measure is required.

Key words: underground caverns, near-fault ground motion, equivalent velocity pulse model, seismic response, artificial simulated ground motion