Potentiality of Microtremor to Evaluate Site Effects at Shallow Depths in the Deep Basin of Santiago De Chile

Abstract eng:
Ambient noise arrays measurements were performed in the deep basin of Santiago de Chile (Chile) where site effects were clearly revealed by the 1985 Valparaiso earthquake. The significant seismic intensities reported for one-storey houses outlined the resonance of a shallow soft sedimentary layer during the Valparaiso earthquake. We look for testing the Horizontal-to-Vertical spectral ratio (H/V) and the more complex array techniques HRFK (High Resolution Frequency-wavenumber method) as a tool to provide qualitative and quantitative information of site effects for the top most soil layers. Although we show the robustness of the H/V method to map the fundamental resonance frequency of the deep basin, we outline its limitation to identify the resonance frequency at shallow depths. We conclude by emphasizing that the H/V method alone may not be enough to assess the seismic hazard in urban area especially when there is a large variety of building type: from small-size residential houses to high rise business buildings. We also show that small-size arrays measurement are a powerful tool to provide the site effect estimates (resonance frequency and amplification factor) for the shallow sedimentary layers.

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