Site Characterization for Strong Motion Stations in Latin American Countries

Abstract eng:
The geotechnical characteristics of a site for a strong motion station have a substantial bearing on understanding the recorded data and its usefulness. Latin American countries, with very limited budgets for strong motion monitoring, have reluctantly restricted their site evaluations to simple visual inspections and, in general, to noninvasive techniques—intensive soil explorations are rare. This article presents a summary of the methodology used in Argentina, Chile, Costa Rica, Colombia, Ecuador, El Salvador, Mexico, Nicaragua, Panama, Peru and Venezuela. Most of the above countries apply similar procedures. Initial site selection criteria considered for a new strong motion instrument station are typically based on the site’s ease of instrumentation, followed by population density, the area’s economic importance, instrument safety and communication accessibility. After these considerations have been examined, the seismic site class is evaluated. In general, once the site has been pre-selected, an initial classification is performed based on visual inspections of surface soils, data from exploration of nearby constructions, and available geotechnical and geological maps of the site. For all recording stations, a detailed study is performed only after the station has been installed and, more commonly, after critical data have already been recorded at the station. Most sites are typically characterized using very basic analytical methods such as horizontal-to-vertical-spectral-ratios (MHVSR) as recorded from ambient vibration (microtremor), or EHVSR from small and large amplitude earthquake recordings. A much smaller set of stations has estimations based on noninvasive surfacewave techniques that include the spatial auto-correlation (SPAC) analysis method and/or the multi-spectral analysis of surface waves (MASW) method, and on rare occasions, estimations are based on soil boring exploration with downhole shear wave velocities measurements.

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