Reversed refraction surveys were conducted along and across the Lomonosov Ridge as part of the 1979 Lomonosov Ridge Experiment. Interpretation of the strike profiles indicates a 5‐km‐thick upper crustal layer with a velocity of 4.7 km/s overlying a 15‐ to 20‐km‐thick layer of 6.6 km/s material. An upper mantle velocity of 8.3 km/s is indicated by a few pn arrivals. High‐amplitude reflection events recorded from this boundary can be successfully modeled by a transition zone of rapidly changing velocity over a depth interval of 5 km. Ray trace modeling of the dip profiles suggests a root structure extending to about 28‐km depth flanked by crust thinning to a depth near 13 km beneath the Makarov Basin and a more gradual thinning to near 16 km beneath the Fram Basin. The similarity between the crust of the Lomonosov Ridge and that beneath the Barents and Kara seas supports the suggestion that the ridge is a slice rifted from the Baltic Shelf.

Several countries are actively investigating the feasibility of using crystalline rock bodies for the ultimate disposal of radioactive nuclear waste. As part of the concept assessment phase in the Canadian nuclear fuel waste management program, a multidisciplinary research investigation is being conducted across the Lac du Bonnet batholith in southeastern Manitoba; no radioactive materials, other than sealed sources or tracers, are to be emplaced within this rock body. The results of a high‐resolution seismic reflection survey, together with information from a number of deep boreholes, demonstrates that major subhorizontal fractures occur at depths of up to 800 m within the batholith. An integrated interpretation of the seismic data with selected borehole logs shows that warm water is flowing up the major fractures from depth. A natural corollary of these results is that a three‐dimensional seismic reflection survey combined with an appropriate exploratory drilling program has the potential for delineating blocks of a rock body that may be relatively unfractured.

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A synthesis of refraction data recorded in 1972 and 1973 in the central Sverdrup Basin with other geophysical data shows major features which correlate well with the regional geological structure. The record sections from the Arctic Archipelago show little coherent secondary energy compared with those from other areas of Canada. Normalization of the sections to remove effects of varying shot size and instrument gain has revealed a significant loss of amplitude and coherence of the upper and mid-crustal phases of the seismic energy on traversing a major northeast-trending structure between Melville and Lougheed Islands. The upper mantle phase (Pn), however, is not abnormally attenuated in its travel beneath the area. The aeromagnetic data reveal a major series of dykes or minor graben, a likely cause of scattering and attenuation of the seismic energy travelling within the crust. These seismic effects and the focal depths of earthquakes suggest that lateral heterogeneities in the crust may extend to near-mantle depths in this area. The age dates available suggest fracture or dyke development progressed from south to north beginning in the Early Cretaceous. The correlation of the recorded seismicity with these structures provides one of the better examples of an active, intraplate tectonic feature.East of King Christian Island (KCI) the refraction results concur with gravity and regional geology in suggesting a major change in crustal and upper mantle structure. Models derived using ray theory indicate a crust which thins from near 40 km beneath the eastern Sabine Peninsula to 32 km west of KCI. East of KCI the Moho may lie at 40 km beneath a complex crustal structure. The average crustal compressional wave velocity is between 5.9 and 6.4 km s−1 and the mean upper mantle velocity is 8.2 km s−1. The present study does not support the existence of a distinct mid-crustal layer with a velocity of about 7.3 km s−1.

The results of three seismological investigations of the crust in the seismically active La Malbaie Region are reported. First arrivals from a reversed reflection-refraction profile within the Charlevoix structure indicate a uniform P, velocity of 6.08 f 0.04 kmls. Secondary arrivals forming discontinuous, sometimes arcuate segments on the record sections are interpreted as subcritical reflections from structural contortions related to impact of the Charlevoix meteorite. A coherent event at 14s may signal reflection from the M-discontinuity near 45 km depth.Analysis of travel times from calibration shots recorded by a network of stations spanning the St. Lawrence River in terms of time-distance profiles, travel time residuals, and numerical models provides excellent support for a model of the Precambrian-Paleozoic contact striking along the north shore and dipping to the southeast about 20" beneath the wedge of 5.5 kmls sediments.Unreversed profiles obtained by recording timed Thetford Mines blasts across a similar network suggests a comparable deep structure beneath the north and south shores, with average crustal velocitiesof 6.8and 6.7 kmls, respectively. A minor mid-crustaldiscontinuity is suggested, and Moho depth is estimated at 42-43 km.The 6.2 kmls upper crustal velocity found for the crater and immediately surrounding area is anomalously low compared to the 6.4-6.5 kmls reported for the eastern shield region. Structural lineations gleaned from satellite imagery suggest an elongated area of impact-related disruption much larger than previously recognized. This expanded area of crustal weakening encompasses and may partially explain the zone of continuing microseismic activity, as well as the low upper crustal velocity of the La Malbaie Region.On rapporte les resultgts de trois etudes sismologiques de la croDte dans la region sismiquement active de La Malbaie. Les premieres arrivkes d'un profil renverse reflexion-refraction a l'interieur de la structure de Charlevoix indiquent une vitesse P,uniforme de 6.08 +_ 0.04 kmls. On interprete les anivees secondaires formant des segments discontinus, quelquefois arques sur des portions de l'enregistrement, comme des reflexions subcritiques des contorsions structurales reliees a l'impact meteoritique de Charlevoix. Un episode coherent de 14 s peut signaler une reflexion de la discontinuite-M a environ 45 km de profondeur. L'analyse de la duree des trajets a partir d'explosions de calibration enregistres par un reseau de stations s'etendant de part et d'autre du fleuve Saint-Laurent en termes des profils temps-distance, des valeurs residuelles de la durte des trajets, et de modeles numeriques fournit un excellent appui pour un modele de contact Precambrien-Paleozo'ique dont la direction est parallele a la rive nord avec un pendage au sud-est a environ 20" sous un coin de sediments dont la vitesse est de 5.5 kmls.Les profils non renverses obtenus par enregistrement des explosions de dates connues a Thetford Mines a travers un reseau semblable suggerent une structure p...