Effects of overburden thickness and slope grade of loess sites on the amplification of peak Acceleration

Loess is widely distributed in China and the Loess Plateau is one of the major areas where strong earthquakes often take place. From the field investigation on earthquake damages caused by Wenchuan Ms 8.0 of 12 May. 2008, the seismic amplification effects were observed. In order to analyze the mechanism of the seismic amplification effects, microtremor surveys were carried out to detect the ground condition and the predominant frequency of the different sites of the same mountain was obtained. Moreover, the typical mesa of loess plateau is studied applying the dynamic finite element analysis method of two dimensions linearly equivalent for dynamic response numerical calculation, with different loess thickness and different slope grades. The magnifications of peak acceleration at the mountaintop and mountainside are obtained under different conditions. It is found that the magnification is related to the loess thickness and slope grades, which is in accordance with the earthquake damages, and the results show that the loess thickness and slope grade are important factors influencing earthquake damage.