Analysis of Microtremor’s HVSR on Different Seismic Site Conditions

Analysis of Microtremor’s HVSR on Different Seismic Site Conditions

Seismic waves are usually amplified by local unconsolidated sediments at specific frequencies during strong motions, that is, the so called site effect, a significant issue in seismic hazard assessment. Dominant frequency of Horizontal to Vertical Spectral Ratio(HVSR) of microtremor is considered caused by a resonance of trapped body and surface waves, which are caused by various natural and artificial sources. Dominant frequencies vary with different subsurface structures. The HVSR of microtremor is therefore an effective tool to be used to find a local resonance frequency, thickness of sediments, etc. Otherwise, the Engineering Geological Database for TSMIP(EGDT) is constructed by the NCREE and CWB, including logging data, e.g. soil parameters, SPT-N, and velocity profiles at more than 400 free-field TSMIP stations. The data from EGDT are very useful for the approach of classifying sites into different seismic site conditions using HVSR. After data processing, HVSR at sites of different classes were also analyzed to discuss the correlation among dominant frequency, thickness of sediments, and S-wave velocity. An important property of microtremor’s HVSR, falling frequency, was learned in this study to help us discriminate different seismic site conditions. Guidelines developed here could be further refined to define a prompt method for classifying sites into different categories using HVSR.