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TitreMulticomponent vibroseismic profiling over high velocity glacial ground: an example from southern Ontario
AuteurPugin, A; Crow, H; Bajc, A; Rainsford, D
SourceSAGEEP, 28th Symposium on the Application of Geophysics to Engineering & Environmental Problems, program and abstracts; par Environmental and Engineering Geophysical Society; 2015.
Année2015
Séries alt.Secteur des sciences de la Terre, Contribution externe 20140248
ÉditeurSociety of Exploration Geophysicists
ÉditeurEuropean Association of Geoscientists & Engineers
RéunionSAGEEP, 28th Symposium on the Application of Geophysics to Engineering & Environmental Problems; Austin, Texas; US; mars 22-26, 2015
Lang.anglais
Medianumérique; en ligne
Formatspdf
ProvinceOntario
SNRC31D/05
Lat/Long OENS -79.8333 -79.6667 44.5000 44.3333
Sujetsforage de la couverture meuble; échantillons carrotés; analyses de carottes de sondage; géologie de la surface; levés sismiques, sol; trous de mine; ondes P; vallées enfouies; géologie des dépôts meubles/géomorphologie; géologie régional
Illustrationslocation maps; tables; seismic profiles
ProgrammeAquifer Assessment & support to mapping, Géoscience des eaux souterraines
Résumé(disponible en anglais seulement)
A 3-D Quaternary mapping project conducted by the Ontario Geological Survey (OGS) in the southern part of Simcoe County involves borehole drilling, airborne geophysics, such as TDEM and magnetics and ground gravity surveys. Geophysical surveys are necessary to define the top of bedrock, including buried bedrock valleys, and the architecture of overlying sediments for evaluating groundwater resources. In support of this project, the Geological Survey of Canada (GSC) carried out a three-line 21.2 km seismic reflection survey. Geophysical logging in two deep boreholes was undertaken to assist with the calibration of the seismic sections.
The seismic survey was performed using and IVI ¿Minivib 1¿ source with a ¿landstreamer¿ three-component geophone array built by the GSC. The landstreamer consists of 72 - 3 kg metal sleds spaced at 1.5 m towed using low-stretch belts. Data were acquired with shot points every 4.5 m. The source vibrates a 140 kg mass in in-line (H1) horizontal mode, using a 7 second nonlinear logarithmic sweep of -2 DB/Oct from 20 to 300 Hz. This type of sweep increases the time spent in the low end of the sweep increases the low frequency energy to enhance shear body wave energy. Data were recorded using seven 24-channel Geometrics Geode engineering seismographs operated in the cab of the Minivib. Only the vertical component of the 24 geophones furthest from the source was recorded in order to obtain a better coverage of the P-wave data acquisition window. Uncorrelated records are collected to allow pre-whitening of the data and careful choice of the correlating function is the first step in the data processing sequence. P-wave sections are derived from processing the first 0.5 sec. (after correlation) of data acquired on the vertical geophones, while S-wave sections are produced using the in-line, H1, component over a correlated window of 2 seconds. Seismic sections are then correlated with borehole geophysical data.
Interpretation of the equivalent compressional (P-) wave section permits delineation of seismic facies sequences. The P-wave velocity is an order of magnitude higher than the shear wave velocity and as a result the vertical resolution of the section is lower. However, the acoustic impedance contrast with underlying materials (coarser sediments, tills or bedrock) is lower than in the case of shear wave. The shear wave data produce remarkably detailed sections over buried valleys down to 150 m.
Résumé(Résumé en langage clair et simple, non publié)
Un projet de cartographie quaternaire a été conduit par la Commission Géologique de l'Ontario (CGO) dans la partie sud du comté de Simcoe qui implique le forage de puits, de la géophysique aéroportée comme de la TDEM, du magnétisme et de la gravite terrestre. Les études géophysiques sont nécessaires pour définir le toit du rocher, incluant les vallées rocheuses enfouies et l'architecture sédimentaire du remplissage des vallées pour évaluer les ressources en eau des aquifères. En support de ce projet, la Commission Géologique du Canada (CGC) a acquis trois lignes de sismique réflexion sur un total de 21.2 km. Des levers géophysiques dans deux puits de forage profonds ont été effectués pour contribuer à la calibration des sections sismiques. L'interprétation des sections en onde compressive (P) et en onde de cisaillement (S) permet une délinéation des facies sismiques. Les ondes de cisaillement produisent des sections remarquablement détaillées sur des vallées enfouies jusqu'à 150 m de profondeur.
GEOSCAN ID295446