Abstract
In order to investigate seismic behavior of a rock tunnel, earthquake observations have been carried out in the Shin Usami Tunnel of JNR's Line, located in Ito City of Shizuoka prefecture. From an analysis of earthquake records observed from July 1983 to June 1985, the following results were obtained.
(1) The direction of the predominant motion of an earthquake in rock which lies sufficiently deep below the surface is not necessarily closely related to the direction of the epicenter.
(2) As for the propagation of an earthquake, the primary wave of the initial motion and the shear wave of the main motion propagate in the upward direction nearly vertically.
(3) The frequencies at the peaks of the amplification function are constant and not influenced by the properties of the earthquake. In the horizontal plane of the rock around a tunnel, no noticeable amplification of the earthquake wave can be seen even in the vicinity of a cavern.
(4) In the cross section of a tunnel, the shearing deformation is significant.
