Study of the S-wave velocity and its error as derived from different microtremor observations

The microtremor data are collected by the active (geophones spread in linear) and passive sources (geophones spread in both linear and L-type) for 8 sites near the strong-motion seismograph stations located in the area of Taoyuan County, Taiwan in this study. For studying the S-wave velocity observation error, 3 different microtremor records are collected at each site for every observation, respectively. To derive the shear-wave velocities, the observations from active source are analyzed by the multichannel analysis of surface waves (MASW) method, whereas, the observations from passive source are processed by the spatial autocorrelation (SPAC) method. Deviation of S-wave velocity at every depth interval is derived by the root-mean-square of the differences between the velocities of single observation as respect to their means. The results show that small deviations of S-wave velocity are found at shallow-depth layers in the observations with active source, whereas, the observations with passive source will have better resolutions for deeper layers. Meanwhile, S-wave velocity as averaged from the depths of 0~30 m (V̅_S,30) and its deviation percentage are also given for all types of observation, the results indicate that the values of V̅_S,30 derived either by active source or by passive source can all satisfy the engineering applications.