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UBC Theses and Dissertations

The use of microtremor measurements for seismic hazard studies in the Greater Vancouver Regional District (GVRD) Teo, Dennis

Abstract

The Greater Vancouver Regional District (GVRD) in the province of British Columbia is located in one of the most seismically active regions of Canada. In this thesis, a method for assessing the seismic hazard potential at GVRD sites using the characteristics of microtremors is evaluated. These characteristics, site predominant periods and relative amplification ratios, were determined by analyzing records of microtremors. The feasibility of using the microtremor characteristics for hazard estimation was investigated. The stability of the characteristics of microtremors at a site is crucial for assessing seismic hazard potential. For the GVRD region, the site predominant periods of microtremors were found to be stable over time. On the other hand, the peak Fourier spectral amplitudes and horizontal-to-vertical spectral ratios tend to fluctuate over time in response to the strength of the input sources. Comparison of spectral characteristics of microtremors and those of low-level earthquake ground motions showed that microtremor measurements can be used effectively to delineate the periods of peak response of sites. At deeper sites (>150 m) the periods of peak response from microtremors may reflect either the dominant response due to resonance in one of the upper strata or the excitation of one of the higher periods at the sites instead of the fundamental periods of these sites. The relative amplification ratio was found to be an inconsistent indicator for comparing the relative seismic amplification potential of sites.

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