Extensive testing of sled-mounted geophone arrays for near-surface (0-4m) layers in floodplain sedimentary facies: Atchafalaya Basin, Indian Bayou, Louisiana

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During November 2003 through June 2004 we conduct extensive seismic tests with traditional geophones mounted on low-cost "channel" steel and wooden sleds. We target human habitation surfaces within the upper few meters (4-5m) of Holocene floodplain deposits in the Atchafalaya Basin, Indian Bayou Wildlife Management Area, Louisiana, U.S. One 5-m-long sediment core is run through a multi-sensor tool to compare magnetic susceptibility, bulk sediment density and electrical resistivity properties. We rank the quality of 24-channel seismic data,collected using multiple P-wave and SH-wave sources. Receivers include 100-Hz vertical- and 14-Hz-horizontal-component geophones. P-wave sources comprise (1) a commercial downhole 12-;gauge pipe-gun, (2) a 0.22 caliber-powered piston gun striking a ∼5 cm-square steel plate, (3) a commercial elastomer-band-accelerated weight (36 kg) drop striking a 30 cm-square aluminum plate and (4) a ∼1.5-kg claw hammer striking a 15-cm-square aluminum plate. We compare both ground-planted and geophones screwed to long (1.2 m, 22 kg) wooden and shorter (0.25 m., 9 kg) steel sleds. SH waves are generated striking the sides of a planted 15-cm-wide I-beam. Geophones screwed to steel sleds collect adequate but noisier data than geophones planted in ground. Because of the high seismic attenuation of reflected P-waves in this sedimentary environment, horizontal-component geophones mounted on heavy (9-kg) steel sleds provide more useful data (refractions) for forward modeling the velocity structure. The shallowest observed shear wave reflected arrival appears from a boundary at ∼19 m depth, below the target depth of 4-5 m. When time and cost efficiency are considered, steel, sled-mounted, horizontal component geophone arrays are recommended for these types of sediments. © 2005 Society of Exploration Geophysicists.

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SEG Technical Program Expanded Abstracts

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