Earthquake Site Class Characterization of Seismograph and Strong-Motion Stations in Canada and Chile

Abstract eng:
Earthquake recording stations, seismographs and/or strong-motion instruments, located on underlying soils are generally installed without comprehensive knowledge or testing of the underlying geologic material in Canada and Chile. To remedy this issue, various in situ geophysical methods are applied to evaluate the underlying ground conditions at earthquake recording stations in Canada and Chile with the overall aim to develop a standard, systematic, and inexpensive procedure for earthquake site classification. The underlying geology at Canadian and Chilean earthquake recording stations is immensely variable and therefore comprehensive to this study's application. At central and southern Chilean strong-motion stations that recorded the 2010 M W 8.8 Maule earthquake, boreholes were drilled to 30-80 m depth and various invasive methods (downhole velocity, laboratory bender element, and standard penetration testing) were performed, as well as passive (ambient vibration) array testing at surface. At northern Chilean strong-motion stations that recorded the 2014 M W 8.2 Iquique earthquake, a combination of active (hammer-impact) and passive surface wave array testing was performed. Combination surface wave array testing is also performed at Canadian seismograph stations in Alberta (western Canada) and Ontario (eastern Canada). For all stations, spectral ratio analysis of ambient vibration and available earthquake recordings is performed. A database of each station’s earthquake site classification according to the respective National Building Code in Canada and Chile is generated – both countries have adopted the six NEHRP (Natural Earthquake Hazard Reduction Program) site classification groupings (A-F) based primarily on the harmonic average shear-wave velocity over the upper 30 meters (i.e., V S30 ) with slightly different bounds in v S30 per site class. Expansion or evolution of v S30 -based site classification to include spectral content (i.e., site period or peak frequency classifications) is included in this study.

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