Applications of microtremor H/V spectral ratio and array techniques in assessing the site effect and near surface velocity structure
应用微动H/V谱比法和台阵技术探测场地响应和浅层速度结构

To rapidly and economically assess the detailed seismic site effects and near surface velocity structures which are crucial for accurate strong motion simulation and efficient seismic hazard prevention, we conducted microtremor array observations and subsequent data processing for the urban areas of the Beijing city. In this paper, using the data collected from several microtremor observation experiments at Wukesong area in the summer of 2007, we estimated the predominant frequencies and their amplification factors of this site with the H/V spectral ratio method. We also investigated the effects of different seismometers and observation times on the H/V spectra curve. Furthermore we retrieved the Rayleigh wave dispersion curve by applying the high-resolution F-K spectral analysis method to the microtremor array observation data and inverted for the subsurface velocity structure using the neighborhood algorithm. The H/V results show that the predominant frequencies in the Wukesong area are about 2.1~2.2 Hz with the lower limit of the amplification factor about 3. The predominant frequencies obtained from the microtremor H/V analysis are stable in this study. The inversion results from the microtremor array data reveal a reasonable subsurface velocity structure in terms of both impedance interface depths and average layer velocities, and suggest that an interface at about 80 meter depth makes the primary contribution to the predominant frequency and the corresponding amplification factor of this site. This study demonstrates that the microtremor technology is a practical and feasible way to assess the seismic site effect and near surface velocity structure at an urban site.