Spectrum-time history ratio method and its application to determination of formation site effect near subway line

We deployed seismometers in subway tunnels and on ground in the vicinity of East Gate of Peking University Station of Beijing Subway Line 4. Using the vibration data obtained, we proposed a data processing method based on independent signals, which we called spectrum-time history ratio method, thus we could obtain stratigraphic site effect and the information of vibration attenuation characteristics from subway vibration data and ground vibration data. Vibration data from different time periods in the same observation point are analyzed and calculated. The results are highly stabilized and proved a good consistency with frequency response characteristics of theoretical transfer function applied in layered half-space medium model based on borehole data. Meanwhile, we also evaluated integrated equivalent attenuation characteristics induced by coupled vibration of tunnel wall and the soil and inelastic absorption of upper layers near the observation points based on the method. Our results indicate that the peak frequencies of site amplification effect of vibration range mainly between 3—10 Hz near the East Gate of Peking University Station. Affected by the vibration of the subway, site resonance exhibits a strong dependence on direction and a spatial variation.