P-WAVE AMPLIFICATION BY NEAR-SURFACE DEPOSITS AT DIFFERENT EXCITATION-LEVELS

Possible nonlinearity in the response of sedimentary layers to inciden t P waves is studied using the strong-motion data from a vertical arra y in Taiwan at the site where a significant nonlinear response to S wa ves had been found. Soil transfer functions are analyzed at different excitation levels with a maximum vertical acceleration at surface reac hing similar to 0.1 g, corresponding to the compressional strain of 7 X 10(-5). Weak-motion and strong-motion transfer functions are compare d. No effects of reduced amplification or change in resonance frequenc ies with increasing strain level were observed, suggesting that the re sponse remained linear in the range of strain under consideration.