Ambient Noise and Site Response: From Estimation of Site Effects to Determination of the Subsoil Structure

Abstract

Damage distribution during large earthquakes is frequently conditioned by site effects. Site effect are best determined usingearthquake data. However, that data is not always available and ambient noise measurements have been used as an inexpensivealternative. Microtremor measurements have been used along two paths to study site effects: estimation of a local transferfunction, and estimation of the subsoil structure (once this structure is known, it is possible to compute expected groundmotion amplification). Currently, the estimation of a transfer function uses H/V spectral ratios almost exclusively. Estimationof the subsoil structure exploits data from array measurements of microtremors applying techniques such as SPAC, ReMi andtime domain analysis of cross-correlation. This paper discusses those two paths and shows the results that were obtained intwo dissimilar examples: Parkway basin and Colima city. It is shown that results need to be validated; it is unsafe to usea single technique. In addition, it is clear that no single technique is adapted to all possible cases.