Characterization of site effects in Montreal, Canada

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.

High‐resolution seismic reflection profiling of neotectonic faults in Lake Timiskaming, Timiskaming Graben, Ontario‐Quebec, Canada

“…Adams & Basham, ; Basham & Adams, ). Seismic risk to large cities, such as Ottawa and Montreal, is compounded by the presence of glaciomarine Leda Clays deposited in the late glacial Champlain Sea and aging urban infrastructure (see Motazedian & Hunter, ; Rosset & Chouinard, ). Major earthquakes occurred in the area in 1732 (Montreal; M5·8) and in 1944 (Cornwall; M5·6) and, as related above, earlier large post‐glacial earthquakes are recorded by post‐glacial landslides along the Ottawa Valley (Aylsworth et al ., ).…”

Earthquake-triggered slumps (1935 Timiskaming M6.2) in Lake Kipawa, Western Quebec Seismic Zone, Canada

“…Such issues loom large across the Shield terrain of eastern Canada in connection with the safe design of mines and nuclear facilities including waste disposal sites. The stability of urban infrastructure on lateglacial marine sediments (Leda Clays) along the Ottawa and St. Lawrence Valleys is also a concern as these Leda Clays exhibit 'quick' behaviour when disturbed (Ma et al, 2008;Motazedian and Hunter, 2008;Rosset and Chouinard, 2008;Lundstrom et al, 2009). Attention focuses on the geologic and geomorphic record of seismic activity in eastern North America such as liquefaction structures, faults, sedimentary dikes and landslides (e.g., Kelson et al, 1996;Ouellet, 1997;Aylsworth et al, 2000;Talwani and Schaeffer, 2001;Tuttle, 2001).…”

Scenario shakemaps for Montreal

“…The NBCC (2010) indicates that Montreal can expect horizontal peak ground acceleration (PGA) of 0.43g with a probability of exceedance of 2% in 50 years, or a 2475-year return period; motions of this intensity could cause significant damage (Adams and Atkinson 2003;Adams and Halchuk 2003;Rosset and Chouinard 2009). Deaggregation from seismic hazard analysis shows that the main contribution to seismic hazard at the 2% in 50 years probability level, for short-to-intermediate periods, comes from the potential for earthquakes of moment magnitude (M)ϳ5 to 6.5 at a distance of <50 km (Atkinson and Goda 2011).…”