Abstract
Nonlinearity of site amplification is examined by using the ground motion records of the 2001 Geiyo earthquake and subsequent smaller events. Comparisons of the site amplifications calculated from the weak and strong motion records show the nonlinear soil behavior during the main shock. The analysis of the amplification factors derived from the records of the Geiyo earthquake together with those of the 1989 Loma Prieta and 1994 Northridge earthquakes indicates that the effect of nonlinearity on peak ground acceleration becomes significant with the strain level in surface soils being larger than approximately 3×10-4 however the nonlinear effect on peak ground velocity is not apparent up to the strain level of about 1×10-3.
