Min/Max Autocorrelation Factors (MAF) are used to perform spectral decomposition of auto- and cross-correlated grain-size distributions (GSD) from samples of glaciofluvial sediments taken along a borehole within a buried valley aquifer. The Sequential Gaussian method is then used to generate realizations of the MAF from which simulated GSDs are recovered by back-transformation. Univariate and bivariate statistics of the simulated GSDs are compared to those of the original data. Transition probabilities of categorical sediment types derived from simulated and original GSDs are also compared.

Geophysical surveys, including shallow seismic reflection profiling and downhole geophysical logging in boreholes, are tools that can be used effectively to identify and delineate buried bedrock valleys and their coarse-grained fills. This paper presents the results of a shallow seismic reflection survey, coupled with information from geological and geophysical logging of a deep borehole, which identified a buried bedrock valley in the glaciated terrain of southern Ontario, Canada. The valley was determined to be similar to100 in deep and similar to2-4 km wide, much larger than predicted on the basis of existing water well records. The deep borehole, located on the westernmost seismic profile, encountered similar to20 m of gravel and coarse sand just above bedrock, but interpretation of the seismic facies in the other profiles suggests that there could be similar to100 m of coarse-grained sediments infilling the similar to2 km wide bedrock valley farther to the east. These data have delineated a potentially significant buried-valley aquifer in an area where previous data analysis had failed to identify any aquifer potential.

Hydrogeological models need to be supported by a clear understanding of the subsurface geology to provide effective assessment, flow modelling, or management of groundwater regimes. This paper illustrates how geophysical and sedimentological data can be used to significantly improve watershed-scale hydrostratigraphic models by advancing our understanding of the subsurface through regional hydrogeological investigations in the Greater Toronto Area. The example of a 3 km shallow seismic reflection survey that traverses a buried channel within Bowmanville Creek watershed, Oak Ridges Moraine, Ontario, illustrates a basis for linking geophysical and sedimentological properties to regional hydrostratigraphic parameters. Seismic reflection methods plus seismic stratigraphy and a well-constrained three-dimensional geological framework have helped to (i) identify regional hydrostratigraphic units, (ii) define properties and trends of these units–facies, (iii) improve depositional models that assist hydrogeological analysis, and (iv) establish a hydrostratigraphic framework within a watershed. The extent, proportions, boundaries, and variation in internal properties of major hydrostratigraphic units could be identified to greater than 100 m depth. Geostatistical analysis of seismic amplitudes was used to provide a quantitative measure of heterogeneity in a glaciofluvial aquifer with inadequate parameter support. Benefits to engineering practice include improved siting of monitors and tests from portrayal of the spatial organization, geometry, and variability of hydrostratigraphic units based on sedimentary architecture and environments of deposition. Hydrogeological modelling can be improved with better knowledge of the geometry of aquifers and aquitards and grid-cell boundaries that correspond with the defined sediment boundaries that control properties.Key words: Oak Ridges Moraine, hydrogeology, seismic stratigraphy, southern Ontario, sedimentology.

High-resolution seismic surveys, including P- and S-wave studies, have been conducted in an area of the Ottawa River valley located 80 km east of Ottawa (Canada). Based on dating of paleolandslides, the existence of paleoearthquake activity has been postulated in this area. The target zone for the seismic survey is characterized by surface disturbance and sediment deformation. P-wave seismic imaging was used to map the overburden–bedrock interface as well as to indicate reflecting boundaries within the overburden. The area of surface disturbance was found to overlie a buried bedrock basin, 8 km in diameter, infilled with a maximum thickness of 180 m of unconsolidated Quaternary sediments. Preliminary results of core logging show the presence of sand overlain by deformed fine sediments within the disturbed area. Shear-refraction studies reveal differences in the velocity–depth profiles between the disturbed area and the surrounding undisturbed areas. The shear-wave reflection method was used to produce a fundamental resonant period map for the area. Surface sediment disturbance was probably due to a combination of ground-motion amplification due to the basin (thick soft sediments) and the presence of water-saturated sand at depth.

Early Cretaceous unconsolidated quartz sand and kaolinitic clay deposits in the lowlands of Nova Scotia are preserved in narrow half-grabens obscured by glacial drift. The Chaswood Formation sediments can be subdivided into three members; upper and lower members dominated by cyclical sand–mud facies of fluvial origin and the middle member with lignitic clay of lacustrine origin. Ferruginous oxisols are common in the fine-grained facies of the upper and lower members. Seismic data indicate that Chaswood Formation strata in the Elmsvale Basin are deformed into steeply dipping faults and fault-related folds (Rutherford Road fault zone). An Aptian–Albian age for this tectonic event is inferred from synsedimentary deformation and from the angular unconformity spanning the Late Cretaceous and Tertiary that truncates the Chaswood Formation. Exhumation of a thick cover of Mesozoic sediment (1–2 km) is needed to account for the preservation of Chaswood Formation outliers after ~80 Ma of erosion. The half-grabens that host the Chaswood Formation were formed in the Mesozoic and were antecedent to the present-day structurally controlled lowlands.

A high-resolution, multichannel, CMP, marine seismic reflection survey was carried out in Lake Simcoe, southern Ontario, Canada, in June 1998, to examine large channel features within the glacial sediments beneath the lake bottom. Over 300 line-kilometers were obtained at close line spacings with an oil-filled hydrophone receiver array and a I cu. in. airgun fired accurately at 5 meter horizontal intervals. Firing on distance was accomplished by integrating a real-time DGPS (Differential Global Positioning System) and a computer-driven triggering system which adjusts the firing rate depending on the ship's velocity. The survey was conducted with an average boat speed of approximately 4 knots (7 km/hour), and multichannel records were recorded on a Geometrics R24 seismograph at 2.2-3 second intervals.Preliminary results show remarkable subbottom detail. Reflections within the glaciolacustrine sequence on the final stacked sections (6-fold) have dominant frequencies in excess of 1 kHz. Simultaneous recording of single-channel seismic data with a Datasonics Chirp II profiler allow comparison of the multichannel stacked sections with this higher-resolution system. Even with the use of a small chamber (1 cu. in.), the airgun data have the advantage of greatly enhanced depth penetration. The bedrock surface can be observed at a depth of similar to 40 m below bottom except in areas where overlying, coarse-grained sediments (including high-velocity tills) are thick (>similar to 20 m). The high resolution of the stacked sections depends on careful processing, which includes spiking deconvolution to whiten the amplitude spectrum, and accurate, closely-spaced velocity determinations. Relative amplitudes were preserved during processing (no automatic gain control was applied), allowing analyses of impedance contrasts and estimates of lithologies to be made. This survey dramatically demonstrates the resolution potential of multichannel marine data obtained with a small airgun source.

Analysis of over 50 line-kilometres of land-based, shallow, seismic reflection profiles has provided a means of investigating the subsurface architecture and stratigraphic relationships of the glacial deposits in and beneath the Oak Ridges Moraine (ORM). The focus of this paper is the role of seismic reflection surveys, and the derived seismic facies and facies geometry, in the development of a well-constrained, regional, conceptual model of the subsurface stratigraphy in the area and the improved inferences these data allow regarding glacial event sequence and process interpretations. The data define four major seismic facies that characterize the complex glacial sequence of the ORM area. High-reflectivity facies (I) can be traced regionally and related to an eroded Newmarket Till surface. Medium (II) and low (III) reflectivity facies are generally associated with coarse-grained glaciofluvial deposits and laterally extensive, glaciolacustrine sequences of sand, silt, and clay, respectively. A chaotic facies (IV) is common within buried channels, and attributed to instability and (or) rapid channel-fill deposition. Seismic geometry (with borehole verification) shows that a broad surface network of channels extends below thick ORM sediments. The channel system is part of a regional unconformity formed on the Newmarket Till (facies I). The buried channels can have steep sides, and their fills frequently include tabular sheets, eskers, and (or) large cross-beds. The observations are consistent with the scenario of sheet flow and channel cutting by high-energy subglacial meltwater and filling with gravel, sand, and silt in succession (facies II and III) as the flows waned.

The “optimum offset” shallow seismic reflection technique was developed for geotechnical and groundwater applications in the early 1980s. The method was based on equipment that was “state of the art” at the time: a 10-bit engineering seismograph, a simple inhole shotgun source, and Apple II personal computers for data processing. In 1985 and 1986, this technique was successfully used in Thailand to assist in understanding the land subsidence problem around Bangkok, which is directly attributable to excessive groundwater withdrawal. The seismic sections acquired in this study were used to map subsurface structure to a depth of about 180 m, which includes several major aquifers beneath the Bangkok Clay. Much of Bangkok’s domestic water is pumped from the so‐called “second aquifer,” 80–130 m below surface, which proved to be an excellent seismic marker horizon showing lateral continuity over distances on the order of kilometers. This observation suggests that there may be good hydraulic connection within this aquifer over large areas. While the technique and equipment used in this study are dated now, the results provide a valuable demonstration of the application of inexpensive shallow reflection methods to a major engineering and groundwater problem that is of concern in many urban centers around the world. It is presented here for its societal relevance in this regard and for its historical aspect as perhaps the first application of shallow seismic reflection profiling in Southeast Asia.

The proper handling of static corrections is an issue that is of critical importance to shallow seismic reflection surveys because of the high frequencies used, the large velocity variations that frequently exist in the near surface, and the shallow depths of investigation. The adaptation of conventional methods of determining static corrections is often inadequate for shallow seismic reflection data. This paper presents a method of handling static corrections which addresses the problem in terms of long-, medium-, and short-wavelength variations in topography and nearsurface velocity variations. An analysis of first-arrival data at intervals along the survey line is used to estimate a layered, near-surface, velocity structure. First-break picking is then used to align the first arrivals to a laterally-interpolated, near-surface, velocity function. This process corrects for medium- (i.e. within spread length), and long-wavelength (>spread length), nearsurface velocity variations, as well as most of the static contributions related to individual geophone locations and elevations (i.e. short-wavelength corrections). Accurate residual statics correct any remaining short-wavelength errors. Finally, topographic variations (long-wavelength) are corrected post-stack. Both model results and application of this method to actual shallow seismic reflection data show this to be a robust and effective method of correcting for statics.

The Geological Survey of Canada and the Nova Scotia Department of Natural Resources have recently completed a joint project which has led to a major discovery of commercially viable deposits of kaolin in the Shubenacadie and Musquodoboit Valleys in central Nova Scotia. The aim of the project was to delineate the three-dimensional distribution of Cretaceous and Quaternary unconsolidated sediments in the study area using shallow seismic reflection surveys, drilling, and borehole geophysical logging. During the three year project a total of 65 shallow seismic test sites and 10 line-km of CDP (12-fold) shallow seismic reflection profiles were acquired, and over 20 new boreholes were drilled within the survey area. Initial seismic test results suggested that there were areas in the Shubenacadie basin where bedrock was at depths greater than 100 m below surface. This was subsequently confirmed by NSDNR drilling. The test sites were used to determine the optimum locations for followup seismic profiling in the Shubenacadie valley (1994) and the Musquodoboit valley (1995). The seismic sections and drilling results have clearly delineated Cretaceous sediments in basins buried beneath glacial cover and have substantially increased the known areal extent of buried Cretaceous basins (from <1 km(2) to >57 km(2) in the Shubenacadie and Musquodoboit valleys alone). Analyses of core samples have shown that these basins may harbour economic quantities of kaolin suitable for use in the paper industry. Presentation of preliminary results of the work in November 1995 resulted in the immediate staking of over 80,000 acres (2,000 claims) in the Shubenacadie, Musquodoboit and Antigonish valleys.

A regional hydrogeological study conducted by the Geological Survey of Canada acquired 35 line-km of 12-fold seismic reflection profiles on or adjacent to the Oak Ridges moraine, north of Toronto, Ontario, Canada. The three-dimensional geometry provided by these data aids in understanding the erosional and depositional processes that occurred beneath the Laurentide ice sheet during the late stages of glaciation. The seismic sections indicate large infilled channels in the subsurface which are interpreted as tunnel channels eroded by large, subglacial meltwater discharges. Two seismic profiles from different areas of the moraine show channel-cutting events of different ages and different types of infilling.

A shallow P‐wave seismic source comparison was conducted at a site near Houston, Texas where the depth to the water table was approximately 7 m, and near‐surface materials consisted of clays, sands, and gravels. Data from twelve different sources during this November 1991 comparison are displayed and analyzed. Reflection events are interpretable at about 40 ms on some 220-Hz analog low‐cut filtered field files, and at 60 ms on most 110‐ and 220-Hz analog low‐cut filtered field files. Calculations and local water well information suggest the 40-ms event is from the top of the water table. Subsurface explosive sources seem to possess the highest dominant frequency, broadest bandwidth, and recorded amplitudes and, therefore, have the greatest resolution potential at this site. Our previous work and that of our colleagues suggests that, given a specific set of site characteristics, any source could dominate the comparison categories addressed here.

Data from a shallow seismic-source comparison test conducted in an area with a water-table depth in excess of 30 m and near-surface velocities less than 330 m/s were acquired from 13 different sources at a single site near Chino, California. The sources included sledgehammer, explosives, weight drop, projectile impacts, and various buffalo guns. A possible reflecting event can be interpreted at about 70 ms. At this particular test site, the lowly sledgehammer is among the best sources to provide data to see the possible reflection. Our previous work and that of our colleagues suggests that any source could dominate the comparison categories addressed here, given the appropriate set of site characteristics.

The availability, in the last few years, of low cost microcomputers and multichannel seismographs has made possible the application of high resolution, digital, seismic reflection profiling to Quaternary problems. Seismic analysis of the subsurface can provide continuous, two dimensional sections containing detailed structural and stratigraphic information. A review of the general principles of shallow seismic reflection methods includes the nature of seismic sources (the use of shotgun shells), the application of the ‘optimum offset’ method, data processing and the issue of site dependency. A brief overview is provided of seismic and sequence stratigraphy. Four case studies illustrate the application of reflection seismic profiling: (1) Champlain Sea sediments (Late Wisconsinan) on the flank of the Gatineau Hills near Quyon, Québec; (2) the definition of bedrock valleys beneath Pleistocene deposits near Shawville, Québec; (3) the fill of a linear depositional basin — Okanagan Valley, British Columbia; (4) the seismic signatures of topset and foreset beds, slope failures and a distributary channel of the Fraser River delta, British Columbia.

The Fraser River delta, the largest delta on the west coast of Canada, has been built into the Strait of Georgia during the Holocene. Drill-hole and seismic reflection records reveal a succession of sedimentary units deposited during early Holocene progradation of the delta. These overlie an irregular surface developed on Pleistocene drift. Mud and silt, similar to sediments presently accumulating off the mouth of Fraser River in the southern Strait of Georgia, are conformably overlain by a thick unit of sandy foreset beds, dipping gently to the south-southwest into Boundary Bay and deposited in a foreslope environment. The foreset unit is sharply overlain by a much thinner topset sequence comprising silt and sand deposited in intertidal, fluvial-channel, and overbank environments, and peat deposited in swamps and bogs. Fifteen accelerator mass spectrometry radiocarbon dates on shell and wood indicate that most of the deltaic sediments south of the Main Channel of Fraser River were deposited between ca. 7500 and 5000 BP. By 5000 BP the locus of sedimentation had shifted from the south, into Boundary Bay, to the west and southwest, into the Strait of Georgia proper.

In recent years, specific requirements of offshore geotechnical site investigations, as well as detailed defense research studies, have stimulated research interest in methods for measuring seismic velocities of sea‐floor sediments on the continental shelves. Investigations have used wide‐angie subbottom reflection measurements (McKay and McKay, 1982), bottom‐laid refraction cables (Hunter et al., 1979), and towed refraction arrays, both on the surface (Hunter and Hobson, 1974) and at depth (Fortin et al., 1987; Fagot, 1983).

This paper is the result of the work of a subcommittee of SEG’s Engineering and Groundwater Geophysics Committee. It recommends a data file format for raw or processed shallow seismic or digital radar data in the small computer environment. It is recommended that this format be known as the SEG-2 format.

We have conducted several source comparisons involving 12‐gauge and 8‐gauge Buffalo guns, a 7.3 kg sledgehammer, and a 75 kg weight drop. The results are strongly site‐dependent. We found that, when the near‐surface consisted of fine‐grained, water‐saturated sediments, the 12‐gauge Buffalo gun produced up to two orders of magnitude more energy than the conventional hammer across a broad frequency range. Under such conditions the gun produced the greatest improvement in energy between 200 and 400 Hz, where it yielded up to ten times more energy than the 75 kg weight drop. This indicates that the Buffalo gun may be particularly useful as a shallow reflection seismic source. However, at sites where the near‐surface materials were coarse‐grained and the water table was well below the ground surface, the advantages of using an in‐hole shotgun source as opposed to a hammer or weight drop were minimal. Nevertheless, in many areas we believe that the Buffalo gun is an excellent source for engineering seismic surveys. It is lightweight and portable (<5 kg), inexpensive to build (<$100 US), simple to use and maintain, and a good source of high‐frequency energy.