Frequency domain electromagnetic and ground penetrating radar investigation of ephemeral streams: case study near the Southern High Plains,Texas |
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Authors: | Jeffrey Burrell Harold Gurrola Kevin Mickus |
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Institution: | (1) Department of Geosciences, Texas Tech University, Lubbock, TX 79409, USA;(2) Department of Geosciences, Missouri State University, Springfield, MO 65897, USA |
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Abstract: | A frequency domain electromagnetic (FDEM) and ground penetrating radar (GPR) study was conducted on an ephemeral stream in
north-central Texas to determine if FDEM and GPR measurements can be combined to determine the electrical characteristics
of current and ancient stream channels. GPR data were collected at several frequencies to image sedimentary structures of
different scale lengths, and to determine the formation porosity and water content of stream sediments. FDEM measurements
were collected using Geonics EM31 and EM34 loop–loop instruments on a profile along the current stream channel and five profiles
perpendicular to the channel. The results indicate that the greater spatial resolution of the EM31 mapped the current and
possible ancient channels better than the EM34, however, the EM34 provided depth information on the formations underlying
the channel sediments that the EM31 could not image. GPR measurements taken along a point bar deposit with 200, 100 and 25 MHz
antennae indicated that the higher frequency antenna better resolved channel structures including laminar bedding, trough
scours and cross-bedding, however, lower frequency antenna (25 MHz) imaged sedimentary structures within the underlying channel
sediments. Common midpoint GPR measurements collected along the point bar deposit were used to estimate the sediment formation
porosity (26%) and the water content, during a dry period, of the unsaturated (12%) and saturated (26 or 100% of the pore
space) sediments. The combined results indicated that the FDEM data should be collected first because of the speed and ease
of measurements. The FDEM data (especially the EM31) pointed to the locations of possible sedimentary structures, which can
then be resolved by using different frequency GPR measurements. |
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Keywords: | Electromagnetics Ground Penetrating Radar Ephemeral Streams Formation Porosity |
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