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TitleMulticomponent vibroseismic profiling over high velocity glacial ground: an example from southern Ontario
AuthorPugin, A; Crow, H; Bajc, A; Rainsford, D
SourceSAGEEP, 28th Symposium on the Application of Geophysics to Engineering & Environmental Problems, program and abstracts; by Environmental and Engineering Geophysical Society; 2015.
Year2015
Alt SeriesEarth Sciences Sector, Contribution Series 20140248
PublisherSociety of Exploration Geophysicists
PublisherEuropean Association of Geoscientists & Engineers
MeetingSAGEEP, 28th Symposium on the Application of Geophysics to Engineering & Environmental Problems; Austin, Texas; US; March 22-26, 2015
Lang.English
Mediadigital; on-line
File formatpdf
ProvinceOntario
NTS31D/05
AreaSimcoe County; Cookstown; Beeton
Lat/Long WENS -79.8333 -79.6667 44.5000 44.3333
Subjectssurficial geology/geomorphology; regional geology; overburden drilling; core samples; drill core analyses; surface geology; seismic surveys, ground; boreholes; p waves; buried valleys
Illustrationslocation maps; tables; seismic profiles
ProgramAquifer Assessment & support to mapping, Groundwater Geoscience
AbstractA 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.
Summary(Plain Language Summary, not published)
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. Interpretation of the equivalent compressional (P-) and (S-) wave section permits delineation of seismic facies sequences. The shear wave data produce remarkably detailed sections over buried valleys down to 150 m.
GEOSCAN ID295446