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The 2005 National Building Code of Canada (2005NBCC) recommended new guidelines for construction in earthquake hazard areas. Estimated horizontal shearing forces at ground surface, resulting from a 1:2475 year return period earthquake, are in part based on the geotechnical/geophysical properties of the near surface at a particular building site. This project has demonstrated the use of geophysical techniques to map the variation of nearsurface geotechnical properties required to establish the seismic shaking properties within the City of Ottawa. Ottawa was chosen for this demonstration since: 1) it is an area of higher seismic hazard under the influence of the West Quebec and Ottawa Valley seismic zones, 2) a wide variation in soil and rock properties exist within the city limits, 3) similar site conditions occur throughout much of the Ottawa-St Lawrence Valley area, and, 4) GSC and university specialists were available locally, thus reducing field costs. Current 2005NBCC guidelines suggest estimates of average shear wave velocity to a depth of 30 m (Vs30) as a primary parameter required to estimate seismic shaking levels. Shear wave velocity measurement techniques were tested and modified for soil and rock conditions within the project area. These included: seismic refraction and reflection site evaluation (685 sites), multichannel analyses of surface waves (MASW-33 sites), downhole seismic measurements (16 boreholes), and multichannel towed seismic reflection profiling techniques (Landstreamer ~25 line-km). Shear wave velocities were measured throughout the soil column (to depths of 100+ m); in addition, shear wave velocities were measured for the differing rock types within the city. Within the survey area, a borehole geology data bank consisting of approximately 21900 entries was re-analysed in terms of shear wave velocity-depth structure based on the field shear wave velocity measurements. A map of the variation of Vs30 was developed from the integration of all borehole and shear wave velocity data. The map shows that low Vs30 values (associated with higher shaking levels) occur in areas where thick soft soils occur. A second map of fundamental site periods was developed from the measurement of both soil seismic properties and depth to bedrock. Estimates of such natural resonant periods of the ground are also required as an aid in estimating the response of structures to seismic shaking. The fundamental site period map indicates that significant long period resonance is associated with areas where thick soft soils occur. Comparison of this map with approximately 200 passive seismic noise measurements (horizontal to vertical spectral ratios HVSR) indicated a well-documented systematic variance. An empirical relationship between the two measurement techniques has been developed. The main products of this research are: 1) A map of Vs30 , following the guidelines of the current 2005NBCC, 2) A map of fundamental resonance period of the soil based on measured shear wave velocities and depths to resonant impedance boundaries, and 3) A data bank (approximately 22000 points) of average shear wave velocity-depth functions including depth to bedrock, bedrock shear wave velocities and fundamental site periods. It is hoped that this information will be a useful guide for city planners, geotechnical engineers, as well as emergency planning organizations. Similar geophysical applications are possible in other areas of the Ottawa- St. Lawrence valleys in the future.

A 3-dimensional (3-D) mapping investigation of Quaternary deposits in the southern part of the County of Simcoe is one of several 3-D mapping projects currently being undertaken as part of the Ontario Geological Survey's groundwater initiative within the Greater Golden Horseshoe area of southern Ontario. Following completion of these projects, a significant proportion of the most densely populated and fastest growing region of the country will be modelled in 3-dimensions, laying the foundation for regional syntheses of subsurface geology. The objective of this project is to develop an interactive 3-D model of Quaternary geology that can: 1) aid in studies involving groundwater extraction, protection and remediation; 2) assist with the development of policies surrounding land use and nutrient management; and 3) help to further understand the interaction between surface and ground waters. A better understanding of the geometry and inherent properties of the Quaternary sediments that overlie bedrock will assist with the development of revised source water protection plans and with the development of a geoscience-based management plan for the groundwater resource. Geoscience data collection was initiated in 2010 and consisted of detailed Quaternary mapping and sedimentological studies of the shallow subsurface, continuous coring to bedrock at 25 locations and a variety of geophysical surveys including: ground gravity, airborne time-domain electromagnetics, downhole geophysical logging and seismic reflection. Supplementary grain size, carbonate, heavy mineral and geochemical analyses enabled an improved interpretation of the subsurface stratigraphy. The information gained from this work resulted in a refined understanding of drift thickness and bedrock topography for the Laurentian trough area as well as the identification of 6 regionally significant chronostratigraphic units further subdivided into 15 layers. The main elements of the model, from youngest to oldest, include: 1) postglacial valley-fill deposits; 2) Oak Ridges Moraine (ORM) and equivalent deposits; 3) Newmarket Till; 4) Scarborough-Thorncliffe Formation equivalents; 5) non-glacial (Sangamon- Middle Wisconsin) deposits and 6) Illinoian and possibly older glacial deposits. Advancements in the understanding of the regional-scale architecture, contact relationships and depositional settings of these elements has allowed for an improved knowledge of the Quaternary history of the region. Notable observations include the identification of a widespread, non-glacial unit in the deep subsurface that likely spans the Sangamon to Middle Wisconsin time interval and the recognition of significant topographic relief of the Newmarket Till, extending from drumlinized uplands into broad valleys previously interpreted as tunnel valleys produced by the catastrophic release of subglacial meltwater. A protracted evolution for these valleys is currently being proposed. The character of groundwater flow within valley settings is more complex than observed in valleys underlying the ORM to the south. In Southern Simcoe County, the valleys are largely infilled with fine-grained units and upward hydraulic gradients commonly inhibit interaction of shallow with deep groundwater flow systems.

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