| 英文摘要 |
Microtremor is one of noninvasive methods which are usually used to estimate site effects. The Engineering Geological Database for TSMIP(EGDT) was used in this study as well as measured microtremor at free-field strong motion stations in Kaohsiung and Pingtung to analyze site effects. The dominant frequencies of the Horizontal to Vertical Spectral Ratio(HVSR) of microtremor were proportional to the Vs30 value. The stations considered in this study are classified according to the Building Seismic Safety Council(BSSC). The Vs30 values indicate that differences exist between shear wave velocities(Vs) in the shallow part of thick sediments at stations of class D and E, but this is difficult to estimate using HVSR. The main advantage of HVSR is its ability to detect discontinuities in velocities such as the interfaces of engineering bedrock and seismic bedrock. Most of the strong motion stations are located in plane areas and are classified as class D, showing no significant variation in Vs at depths. Stations of class C are mainly distributed in piedmonts and show a larger variation in their Vs values. Vs values at class B stations are relatively low; only one station in this study had a Vs30 value higher than 1000 m/s. Two stations from the total 62 drilled stations in this area are classified as class E. The distribution pattern of dominant frequencies was found to be comparable with the Vs30 map provided by the EGDT. The dominant frequency was lower than 2 Hz in the plane area, over 4 Hz in the mountains, and lower than 1 Hz for several near the coast. One exception was the station labeled KAU003 which had a coastal location and a dominant frequency of over 10 Hz. This exception is due to the limestone geology at this station. The similarity between the dominant frequency and Vs30 maps demonstrates that HVSR can recognize different seismic site conditions by indicating changes in sedimentary depths. |
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