ON THE SPECTRAL CHARACTERISTICS OF GROUND MICROTREMOR IN COASTAL AREA OF FUJIAN

The ground micro-tremor signals were observed in Fuzhou, Quanzhou and Putian of Fujian Province, and the signals are analyzed by fast Fourier transform method. The result shows that at the sites with greater thickness of overburden layers intercalating a thick weak layer, the rigidity of the ground is low, the frequency band is wider, the frequency energy is rather disperse, the peak frequency is lower with predominate frequency of 1～5Hz commonly; However, the sites with thinner of overburden layers, and greater rigidity of the ground, the frequency band is narrower, and the peak frequency is higher with predominate frequency of 8～11Hz. Soft soil can filter high frequency signals, but can amplify low frequency signals.