In the case the epicenter of an earthquake is located very close to a densely populated urban area, extensive damage may be caused in that area by the high frequency components of the seismic waves that interact with the structures before attenuation. From the structural damage caused by such an earthquake, it is possible to back-analyze the characteristics of the associated seismic waves. In particular, underground stlUCtures such as tunnels vibrate with their surroundings and they are expected to function as sensors that detect waves of specific frequencies. In this contribution, the characteristics of the seismic waves associated with the 1995 Hyogo·ken Nanbu (Kobe), Japan Earthquake are estimated from the earthquake-induced damage to a tunnel located very close to the epicenter. It is shown that the damage observed in that tunnel was possibly caused by vertical oscillations, not by a horizontal shear disturbance.
Failure of underground structures due to an earthquake is rare. For example, on the occasion of the 1995 Hyogo-ken Nanbu (Kobe), Japan Earthquake, nearly 180,000 buildings on the surface were severely damaged or destroyed in the industrially developed Kobe and Osaka (Hanshin) region during and after the strong ground motion that lasted for some 20 seconds. In contrast, only a few underground facilities were damaged (Earthquake Engineering Research Center 1995, EQE International 1995, Takada & Morikawa 1995, Koyama et al. 1996).