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Site-Response Spectra for POLARIS Station Sites in Southern Ontario and Quebec

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	INTRODUCTION

 
Local geologic and soil conditions can greatly increase the intensity of earthquake ground shaking (Kramer 1996). These local site effects are particularly significant at sites with deep, soft soil deposits, although hard rock sites may also exhibit amplification (Siddiqqi and Atkinson 2002). Estimation of this localized site response can be accomplished using theoretical or empirical methods. Theoretical modeling requires extensive characterization of a site's near-surface geology, as well as the use of sophisticated computing methods. In contrast, empirical approaches require only ground-motion data records from the site. The relative ease of application has popularized the use of empirical methods in investigating site response.

Ground-motion records have become readily available at a number of Canadian sites, owing to the recent deployment and subsequent expansion of the Portable Observatories for Lithospheric Analysis and Research Investigating Seismicity (POLARIS) seismograph network (Eaton et al. 2005). In this study, empirical site-response spectra were produced for 11 stations of the POLARIS Ontario (POLO) array of POLARIS (Figure 1 and Table 1). A variety of near-surface conditions exist at these sites. While most are located on competent Precambrian bedrock, others rest on fractured Paleozoic bedrock, soil, or a combination of soil and manmade fill. An additional, temporary, soil station was also studied (Figure 1 and Table 1). Installed near a cement quarry in St. Marys, Ontario, this station collected data over a weeklong period.

Department of Civil and Environmental Engineering
University of Western Ontario
London, Ontario, N6A 5B9, Canada
helnaggar@eng.uwo.ca
(H.E.N.)