Geospatial modelling of shear-wave velocity and fundamental site period of Quaternary marine and glacial sediments in the Ottawa and St. Lawrence Valleys, Canada

摘要

The shear wave velocity of surficial sediments (V-S) and the fundamental site period (T-O) are important parameters for analysis of the free-field seismic response. Their spatial distribution in the Ottawa and St. Lawrence Valleys, Canada, was determined applying a standardized method consisting of (i) updating the Quaternary geology; (ii) classifying the surficial units with similar physical properties into three broad categories: upper sandy sediments, intermediate clayey sediments and basal glacial and non-glacial deposits; (iii) delineating the spatial thickness of each category by way of 3D geologic modelling; (iv) sorting of available geophysical data with respect to each individual category and assigning representative V-S relationships: a power velocity-depth function for sand and clay units combined, V-S=119 + 8.1 Depth(0.5) (m/s), and a constant interval V-S equal to the observed geometric mean velocity for glacial and non-glacial deposits, V-S=385 (m/s). The respective T-O values were computed as the ratio between the soil thickness and the average V-S from ground surface to the bedrock. Validation of model results was conducted with V-S and T-O field data and available T-O estimates from detailed urban-scale seismic zonation studies. The analyses of the uncertainty originating from the variation of the V-S measurements showed that the standard deviations were roughly one-third of the modelled V-S and T-O values. Crown Copyright (C) 2016 Published by Elsevier Ltd. All rights reserved.