CGRG Bibliography of Canadian Geomorphology
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Author : Crow, H.; Hunter, J.A.M.; Brooks, G.R.; and Motazedian, D.
Date : 2011.
Title : Stop 2-1: Seismic microzonation hazard mapping in the Ottawa area.
Publication : Deglacial history of the Champlain Sea basin and implications for urbanization; Joint annual meeting GAC-MAC-SEG-SGA, Ottawa, Ontario, May 25–27, 2011; Fieldtrip guidebook. Russell, H.A.J.; Brooks, G.R.; and Cummings, D.I. (Editors). Geological Survey of Canada Open File
Issue : 6947.
Page(s) : 46-51.
Abstract
The nature of earthquake seismic waves propagating through the earth depends on the source mechanism, the depth of the source, and the character of the rock types along the travel path to a particular site. The character of the shaking at a specific location on the ground surface (amplitude, frequency and duration) is additionally affected by the geologic materials over the last few hundred meters (or less) of the propagation path. This phenomenon arises because seismic energy is modified by areas of dissimilar sub-surface geology and soil conditions as it propagates towards the ground surface. The energy can be either amplified or attenuated by a number of factors that may act in combination depending on the local setting, including: - impedance contrast amplification, caused by shear-wave velocity contrasts between rock and overlying soil layers; resonance amplification, caused by the repeated reflection of seismic energy within a soil layer between the ground surface and the boundary with underlying stiffer strata; basin curvature effects, caused by focusing-defocusing effects of the subsurface geometry; and; basin edge effects, caused by the generation of Rayleigh and Love waves across the surface of a sediment-filled basin. The net effect is that the ground motion often is greater on areas of softer soil than on stiffer soil or bedrock with the result that damage tends to be greater in areas of soft soil (BSSC, 1995). The amplification of earthquake shaking has been a major factor influencing damage distribution and severity during many earthquake disasters, for example, the 1985 Mexico City, 1989 Loma Prieta, 1994 Northridge and 1995 Kobe events (see Seed et al., 1988; Borcherdt and Glassmoyer, 1992; Holzer, 1994; Olshanky, 1997; Ishikawa et al., 2000). The influence of ground motion amplification for building design is recognized in the 2010 National Building Code of Canada (2010 NBCC) (see Finn and Wightman, 2003). The code uses a seismic site classification system that characterizes the underlying geologic materials at a given location for the purpose of defining amplification factors that modify the design ground motion for building design.
Bibliography of Canadian Geomorphology