We develop a method to determine the boundary shape of basin structures using seismograms observed on the surface through a waveform inversion scheme. Our method is based on the fact that seismic waves observed at stations on the surface are affected not only by the local structure beneath the observation point but also by the whole basin structure. This fact suggests a possibility to determine the boundary shape by using the seismic records at only a few surface stations. This paper examines numerically how to determine the boundary shape from observed records on the surface in the case of the two dimensional SH problem. For simplicity, we parameterize only the boundary shape, i. e. the thickness variation of the sedimental layer. This inversion is performed iteratively since the problem we deal with is a non-linear inverse problem. When an appropriate model is given, we can evaluate the boundary shape accurately even though the waveform data at only a few surface stations are given.