Nonlinear seismic amplifications and associated nonlinear soil properties are investigated based on the vertical array records obtained during the 1995 Hyogoken-Nambu earthquake at four sites at very different distances from the earthquake fault zone. These accelerograms were recorded in surface soil layering systems of about 100 m thick consisting of fill, Holocene and Pleistocene or rock base layers. In this research, amplifications in acceleration and velocity between the base and the surface for the main shock and aftershocks are first examined in terms of S-wave velocity ratio between the two levels. A correlation can be found between the amplification and the velocity ratio for linear site responses in the aftershocks, while the amplification is evidently lower for nonlinear response in strong seismic motions for the mainshock. The amplification in acceleration or velocity obviously decreases with increasing input at the base level, indicating remarkable nonlinear amplification characteristics. The acceleration amplification becomes less than unity for base acceleration larger than 0.4 G-0.9 G while velocity amplification stays above unity even for a very large base velocity. Based on the mainshock records, variations in the shear modulus and the damping ratio in the surface soil layers are then evaluated by means of an inversion analysis assuming 1-D vertical SH-wave propagation. A clear strain-dependency can be found in the back-calculated modulus and damping, which are consistent with previous laboratory test results for each kind of soils.