We identify shear-wave propagation and evaluate nonlinearity of soil using weak and strong motions observed at a vertical array at Kuno district in the Ashigara Valley which forms a sedimentary basin. As a result, vertically propagating shear waves are seen in the main part of weak and strong motions and just after the main part of the strong motion. It is pointed out based on an inversion method that the main part of the strong motion has the potential of making the surface soil nonlinear, but that the soil returns to the linear range just after the main part.
