Assessment of the spatial variability of site response in Southern Ontario

• Autores: Sebastian Braganza, Gail M. Atkinson, Sheri Molnar
• Localización: Seismological Research Letters, ISSN 0895-0695, ISSN-e 1938-2057, Vol. 88, Nº. 5, 2017, págs. 1415-1426
• Idioma: inglés
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• Resumen

  • In southern Ontario, Canada, site amplification plays a major role in the interpretation of ground motions and felt shaking during earthquakes. Sediments in the region vary from soft to stiff and overlie very hard glaciated bedrock, providing a strong impedance contrast that results in pronounced amplification of horizontal-component motions. Generally, the peak frequency of amplification (f peak) is inversely related to the depth to bedrock.

    In southern Ontario and many other parts of eastern North America, f peak is the most important site-response parameter.

    In this study, we measure the spatial variability of f peak within a 1 km distance of 10 seismograph stations in southern Ontario. Establishing spatial variability of f peak is useful for assessment of regional site response and its uncertainty; we can estimate site response if f peak is known, and thus it is important to know to what distances the value of f peak is spatially stable.

    Using ambient noise records, f peak is measured from horizontal-to-vertical (H/V) spectral ratios at a number of locations at increasing distance from each seismograph site. Ambient noise H/V amplification ratios are compared with those obtained using weak-motion earthquake recordings at the station. We find that, on average, log10
    f peak as measured by microtremor survey observations is within 0.13 units of the value recorded at the seismograph station (using H/V from earthquake records) for survey sites within 1 km of the station.