Recognition soil nonlinearity area applying the time-frequency analysis method in Wenchuan earthquake

• Main Authors: Hsuan-jui Hsu, 許軒瑞
• Other Authors: Kuo-Liang Wen
• Format: Others
• Language: zh-TW
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/85911313955181651563

碩士 === 國立中央大學 === 地球物理研究所 === 98 === Using time-frequency analysis to determine the time variation soil response is the new development method in the past few years. It could effectively observe the predominant frequency variation with time and de-amplification when the strong seismic waves pass into the surface soft soil layer. In this study, the May 12, 2008 China Wenchuan earthquake data were used. After the baseline correction, using the time-frequency analysis combined single-station spectral ratio with the short time Fourier transform, the resulting time-frequency diagram clearly show the predominant frequency shift to low-frequency in the strong seismic wave part. When amplitude change to small, the predominant frequency will recover, but most couldn’t return to the value before the arrival of strong shaking. The soil stations classified to possible non-linear response as the predominant frequency shifted 0.2 Hz~0.6 Hz. The clear non-linear response stations which predominant frequency shift greater than 0.6 Hz. The possible non-linear response stations mostly located at PGA area larger than 50 gal. The clear non-linear response stations mostly located at PGA area larger than 200 gal. The observed soil liquefaction points and the non-linear response stations located at same areas in three regions along the fault.