Geophysical and geotechnical data are presented from different sites in eastern Ontario where variable geotechnical properties of Champlain Sea sediments (‘Leda Clays’) are found. Sites range from thick “undisturbed” silts and clays, to “disturbed” geologically similar soils (earthquake triggered landslides and other deformed materials). High-resolution seismic profiles provide stratigraphic context for some of the boreholes drilled in the study area. Downhole geophysical logs from 14 boreholes are compared to core sample measurements of porosity, sensitivity, and porewater conductivity to develop useful empirical relationships. According to these relationships, silt and clay sediments can be sensitive or quick when formation conductivity drops below 100 mS/m. Conversely, silts and clays with elevated conductivities (>250 mS/m) are rarely sensitive. Salinity values calculated from porewater conductivity indicate sensitive or quick behaviour may be expected in leached soils when salinity drops below 2 g/l.

In the Montérégie region, east of Montreal, Quebec, Canada, high-resolution compressional (P-) and shear (S-) wave reflection sections were obtained using a vibratory source and three-component (3C) landstreamer data acquisition system during field programs carried out in 2009 and 2010. The work was part of a strategy to improve the knowledge and understanding of groundwater resources within the glacial and postglacial sediments in the region. The >100 line-km of seismic profiling is an excellent example of hydrogeophysics, providing detailed information on the depth to bedrock, the architecture and stratigraphy, and physical properties of the overlying sediments on both the regional and local scales (hydrostratigraphic mapping), as well as insights into fluid (water and/or gas) transport through the surface aquitard. Correlations of porosity and shear-wave velocity in the region also allow some estimation of the variation in subsurface porosities for hydrogeological modeling.

Multi-component high resolution seismic reflection profiling has been extensively tested over a wide variety of ground surfaces across the southern provinces of Canada, showing new potential for applications of the method in groundwater and natural hazards research. The near-surface shear-wave reflection method using vibratory sources and short spacing land streamers equipped with three-component receivers is an excellent tool for accurately characterizing shear-wave velocities and recording optimal, non-aliased shear-wave data in the most polarized direction. A small portable multi-component vibrator developed at the Geological Survey of Canada (GSC) named 'Microvibe' provides higher frequency S-wave and P-wave signals than can be acquired with a Minivib I. In this paper we show that the shear-wave polarization can vary with depth and it may be necessary to combine multiple components together to achieve an optimized stacked section. Significant velocity anisotropies of up to 15% have been observed between the horizontal and vertical directions when using this multicomponent Microvibe source. We make key recommendations based on time and space sampling recording windows for successful near surface PP-wave, PS-wave and SS-wave seismic reflection surveys. Using field examples and velocity measurements, we show the complexity of velocities in non-homogeneous media in the near surface.

Two examples of multicomponent shear (S)-wave, shallow, seismic reflection profiling from urban en-vironments in eastern Canada are presented to examine the benefits of shear-wave reflection data and the latest developments in acquisition methodology, as well as our evolving understanding of the complex nature of seismic-wave propagation. In “soft” soils characterized by low shear-wave velocities, high-resolution shear-wave reflection sections can be obtained, with the highest-resolution data related to horizontal or vertical components of motion. Multicomponent recording provides the capacity to record valuable shear-wave velocity information for earthquake amplification and engi-neering investigations in urban environments.

The Annapolis-Cornwallis Valley Aquifer Study was a regional hydrogeological study focusing on major aquifer units of the most important agricultural area of Nova Scotia. The study area covered 2100 km2, and included sedimentary rocks of the Wolfville and Blomidon formations, as well as part of the North and South mountains bordering the valley. The surficial sediment cover is mainly composed of glacial tills, but sand and gravel units are also present in the eastern part of the valley. The main objectives of this project were to improve the general understanding of groundwater flow dynamics and to provide baseline information and tools for a regional groundwater resource assessment. The main bedrock aquifers of the Valley are located in the Wolfville and Blomidon formations, which are composed of lenticular bodies of sandstone, conglomerate, shale and siltstone in variable proportions. The aquifers are often confined and the flow is topographically-driven. Their hydraulic conductivities are in the range of 10-6-10-5 m/s. Good aquifers, though limited in extent, can also be found in the sand and gravel units, with hydraulic conductivities on the order of 10-4 m/s. Groundwater recharge was estimated to range between 115 and 224 mm/a over the entire study area. The vulnerability study showed that bedrock aquifers are typically less vulnerable than surficial aquifers, with the Wolfville Formation being the most vulnerable bedrock formation. Groundwater of the Valley is generally of good quality, although nitrate levels are of concern in several areas.

Downhole seismic velocity logging techniques have been developed and applied in support of high-resolution reflection seismic surveys. For shallow high-resolution reflection surveying within unconsolidated overburden, velocity-depth control can sometimes be difficult to achieve; as well, unambiguous correlation of reflections with overburden stratigraphy is often problematic. Data obtained from downhole seismic logging can provide accurate velocity-depth functions and directly correlate seismic reflections to depth. The methodologies described in this paper are designed for slim-hole applications in plastic-cased boreholes (minimum ID of 50 mm) and with source and detector arrays that yield similar frequency ranges and vertical depth resolutions as the surface reflection surveys. Compressional- (P-) wave logging uses a multichannel hydrophone array with 0.5-m detector spacings in a fluid-filled borehole and a high-frequency, in-hole shotgun source at the surface. Overlapping array positions downhole results in redundant first-arrival data (picked using interactive computer techniques), which can be processed to provide accurate interval velocities. The data also can be displayed as a record suite, showing reflections and directly correlating reflection events with depths. Example applications include identification of gas zones, lithological boundaries within unconsolidated sediments, and the overburden-bedrock interface. Shear- (S-) wave logging uses a slimhole, well-locked, three-component (3-C) geophone pod and a horizontally polarized, hammer-and-loaded-plate source at ground surface. The pod is moved in successive 0.5- or l-m intervals downhole with no redundancy of overlapping data as in the P-wave method. First-arrival data can be obtained by picking the crossover onset of polarized energy or by closely examining particle-motion plots using all three components of motion. In unconsolidated sediments, shear-wave Velocity contrasts can be associated with changes in material density or dynamic shear modulus, which in turn can be related to consolidation. Example applications include identification of a lithological boundary for earthquake hazard applications and mapping massive ice within permafrost materials.

The Geological Survey of Canada commissioned a helicopter-borne time-domain electromagnetic (HTEM) survey over a 1062 km(2) area of the Spiritwood Valley in southern Manitoba in order to test the effectiveness of airborne time-domain electromagnetics for mapping and characterizing buried valley aquifers in the Canadian Prairies. The data exhibit rich information content and clearly indicate the broader Spiritwood Valley in addition to a continuous incised valley along the broader valley bottom. We detect complex valley morphology with nested scales of valleys including at least three distinct valley features and multiple possible tributaries. Conductivity-depth images (CDI) derived from the HTEM decays indicate that the fill materials within the incised valleys are more resistive than the broader valley fill, consistent with an interpretation of sand and gravel. Comparison of ground-based electrical resistivity and seismic reflection data allow for the evaluation of CDI models. Lateral spatial information is in excellent agreement between data sets. However, CDI results tend to underestimate the dynamic range of electrical conductivity while overestimating depths to valley bottoms; these issues may be associated with system limitations, algorithm limitations or differences between data types. The integrated data sets illustrate that HTEM surveys have the potential to map complicated buried valley aquifers at a level of detail required for groundwater prospecting, modelling and management.

The Geological Survey of Canada commissioned a helicopter-borne time-domain electromagnetic (HTEM) survey over a 1062 km2 area of the Spiritwood Valley in southern Manitoba to test the effectiveness of airborne time-domain electromagnetics for mapping and characterizing buried valley aquifers in the Canadian Prairies. The HTEM data exhibit rich information content; apparent conductivity maps clearly image the Spiritwood Valley in addition to a continuous incised valley along the broader valley bottom. We detect complex valley morphology with nested scales of valleys including at least three distinct valley features and multiple possible tributaries. Conductivity-depth images (CDI) derived from the TEM decays indicate that the fill materials within the incised valleys are more resistive than the broader valley fill, consistent with an interpretation of sand and gravel. Comparison of ground-based electrical resistivity and seismic reflection data allow for calibration of CDI models. Lateral spatial information is in excellent agreement between data sets. The seismic data reveal the presence of additional valley features that are not imaged by the HTEM data as having a distinct electrical signature, possibly due to diamicton fill. The CDI model underestimates the dynamic range of electrical conductivity while overestimating depths to valley bottoms; these issues may be associated with system limitations, system bandwidth, algorithm limitations and penetration depth. The integrated data sets illustrate that HTEM surveys have the potential to map complicated buried valley aquifers at a level of detail required for groundwater prospecting and management.

The Geological Survey of Canada (GSC) Aurora cored borehole intersects the Yonge Street aquifer (YSA), an important groundwater source in Ontario. The borehole, sited along a 7 km long seismic profile, was drilled in order to provide data to improve sustainable use and management of groundwater in Aurora well fields and the regional aquifer system. Results provide high-quality hydrostratigraphic reference data, geological context, and a prospecting model for this significant buried-valley aquifer. The improved conceptual hydrogeological model offers a plan to effectively stress and assess the YSA system. A 130 m sedimentary succession unconformably overlies subhorizontal Whitby shale and a low-relief bedrock surface with no defined valleys. Gas seeping from the shale is trapped in Thorncliffe Formation, a regional aquifer below confining aquitards. The regional aquifer occurs below ~209 m a.s.l. and is a 80 m thick, fining-upward, sand and gravel sequence. It appears to represent a portion of a northeast-southwest-oriented channel, esker, and subaqueous fan system that fed Thorncliffe Formation aquifer sediments to the south. The newly identified aquifer system occurs above a regional unconformity within the succession. A 25 m thick Newmarket Till and silt-clay rhythmite sequence confines this aquifer. This aquitard drapes into Aurora basin, a possible pre-existing sediment valley. High clay content in aquitard rhythmites may allow conductivity logs to map it as a marker horizon. The overlying Oak Ridges Moraine (ORM) aquifer occurs as a 30 m thick gravel-sand-mud sequence above a second regional unconformity within the succession. This channel fill sequence is thinner than nearby 100 m thick ORM channel sediments.

A large integrated data set of cores, outcrop data, and seismic transects from the mud-buried Vars-Winchester esker in the Champlain Sea basin, Canada, was studied to gain insight into how muddy glaciated basins fill with sediment, and how esker sedimentary systems contribute to this process.Three stratigraphic units-a till sheet over carbonate bedrock, the Vars-Winchester esker, and overlying Champlain Sea mud-are identified in the data set. The till is massive, mud rich, carbonate rich, and drumlinized. The esker is also carbonate rich, and rests erosively on till or bedrock. It consists of two elements, a narrow gravelly central ridge and a broad sandy carapace. Three units comprise the overlying mud package: gray carbonate-rich rhythmites, massive bioturbated mud, and carbonate-poor, red-andgray rhythmites.A sequence stratigraphic model is proposed to explain these observations. Emphasis is placed on gradual ice-front translation superimposed by rapid meltwater events. The esker is interpreted to have been derived from the underlying till by water that flowed through a subglacial conduit (R-channel), within which the narrow gravelly central ridge was deposited. Most mud and finer sand bypassed the conduit and was deposited proglacially on the floor of the Champlain Sea, first as sandy outwash and, farther basinward, as muddy carbonate-rich rhythmites. Gradual ice-front retreat superposed distal facies over proximal facies, generating the upward-fining succession that starts with the esker gravel and ends with muddy rhythmites. Most esker sediment appears to have been deposited during rapid, jokulhlaup-like floods that punctuated gradual retreat. Discharges are estimated to have been high, possibly on the order of several hundred to, perhaps more commonly, several thousand cubic meters per second. The chaotic and random-looking appearance of the resultant sedimentological signatures in the esker sensu stricto is sharply contrasted with the regularity of the muddy rhythmites. If the rhythmites are indeed correlative to the esker, which seems reasonable given their geochemistry and the fact that their volume scales to the volume of mud in the till, the flood events that deposited the esker must have been seasonally mediated, and the basin water must have attenuated the flood signal, resulting in a rhythmic "on-off" signature in more distal portions of the system. The regularity of the rhythmites does not betray the chaotic nature of the esker sensu stricto, and vice versa. Studying either one in isolation would lead to a very different "end-member" impression of how eskers form and how esker sedimentary systems operate during the infilling of glaciated basins.

At some sites near Ottawa, Ontario, thick glaciomarine sediments deposited in the Champlain Sea after the final retreat of the Winsconsinan icesheet ∼11,000 years ago show evidence of severe “disturbance” by ground motions during a prehistoric earthquake(s). The Geological Survey of Canada has been investigating these areas to better understand seismic site response and paleoseismicity. This paper presents results obtained with 3-component seismic reflection surveys over such disturbed terrains. Shallow seismic reflection surveys are used to provide subsurface architectural and stratigraphic information. In Champlain Sea sediments, high-resolution compressional (P-) and shear (S-) wave reflection sections have been obtained using a vibratory source/landstreamer data acquisition system. Where the large-scale depositional structure of the fine-grained marine sediments has been disrupted and/or liquefied, the shear wave reflection data quality can be highly compromised. This is interpreted to indicate that the disturbed ground is scattering shear wave energy at the wavelength scale (∼ 1 metre). In contrast, P-wave sections are not degraded in quality to the same extent since the signal wavelengths are longer and the velocity is strongly influenced by interstitial porewater. Comparison of compressional and shear wave data from areas of disturbed ground can provide information on the thickness of the soft fine-grained glaciomarine sediments and the underlying bedrock topography, as well as give new insights into the properties of the disturbed sediments. Such information can lead to better hazard and risk assessments throughout the Ottawa Valley-St. Lawrence Lowlands region of eastern Canada where similar glaciomarine deposits are found.