Characterization of site effects in Montreal,Canada |
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| Authors: | P Rosset L E Chouinard |
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| Institution: | (1) World Agency of Planetary Monitoring and Earthquake Risk Reduction, Geneva, Switzerland;(2) Department of Civil Engineering & Applied Mechanics, McGill University, Montreal, Canada |
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| Abstract: | Recent destructive earthquakes have clearly shown that near-surface geological conditions play a major role in the level of
ground shaking in urban areas. In Canada, Montreal is ranked second for seismic risk after Vancouver considering its population
and regional seismic hazard. The city is largely built on recent unconsolidated marine and river deposits and most of its
infrastructure is old and deteriorated. A seismic risk project that includes a combined methodology for site effects zoning
in large cities, using microtremor measurements (H/V method) coupled with 1D numerical modelling (SHAKE91), has been initiated. The experimental approach gives good estimates
of the fundamental frequency of soft deposits, while the numerical approach provides good estimates of the soil response in
terms of amplification factor related to frequency. Main mechanical properties of soft soils were compiled from various data
available, and a sample of input rock motions from real and synthetic earthquakes was used to compute soil response. The influence
of marine clays on soil response is significant and is well correlated with thickness of these deposits. PGA amplification
factors range from 2 to 4 at frequencies from 2 to 7 Hz, with some occasional larger values. The results demonstrate that
the methodology used for our study is both fast and efficient to determine the influence of soft soils in urban environments.
Such studies are essential for the effective deployment of seismic instrumentation, land-use planning and seismic mitigation. |
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| Keywords: | Seismic site effect Ambient noise method 1D modelling Microzonation Montreal Mitigation |
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