Development of an NEHRP map for the Orleans suburb of Ottawa, Ontario

Abstract

The average shear-wave velocity to a depth of 30 m (Vs30) has been obtained for 73 sites in the Orleans area in the northeast part of the City of Ottawa. Measurements of Vs30 were made using both ground surface reflection and refraction methods. In addition, borehole data was used to estimate Vs versus depth profiles using average Vs values assigned to distinct geological units. High values of Vs (>1500 m/s) were obtained in areas of thin surficial sediments overlying Paleozoic bedrock, and low Vs values (<180 m/s) were calculated in areas of thick late–post-glacial clay. The Vs30 values have been used to prepare an NEHRP map for the study area. Much of the suburb of Orleans is classified as NEHRP zone E, whereas the perimeter areas and some isolated central areas are classified as zones ranging from zone D to zone A. The presence of thick unconsolidated late–post-glacial sediments deposited in the Champlain Sea is the main contributing factor to the wide range of average shear-wave velocities in the study area.