15 research outputs found
Recording seismic reflections using rigidly interconnected geophones
This is the publisher's version, also available electronically from "http://library.seg.org".Ultrashallow seismic reflection surveys require dense spatial sampling during data acquisition, which increases their cost. In previous efforts to find ways to reduce these costs, we connected geophones rigidly to pieces of channel iron attached to a farm implement. This method allowed us to plant the geophones in the ground quickly and automatically. The rigidly interconnected geophones used in these earlier studies detected first‐arrival energy along with minor interfering seismic modes, but they did not detect seismic reflections. To examine further the feasibility of developing rigid geophone emplacement systems to detect seismic reflections, we experimented with four pieces of channel iron, each 2.7 m long and 10 cm wide. Each segment was equipped with 18 geophones rigidly attached to the channel iron at 15‐cm intervals, and the spikes attached to all 18 geophones were pushed into the ground simultaneously. The geophones detected both refracted and reflected energy; however, no significant signal distortion or interference attributable to the rigid coupling of the geophones to the channel iron was observed in the data. The interfering seismic modes mentioned from the previous experiments were not detected, nor was any P‐wave propagation noted within the channel iron. These results show promise for automating and reducing the cost of ultrashallow seismic reflection and refraction surveys
Source-dependent frequency content of ultrashallow seismic reflection data
This is the publisher's version, also available electronically from "bssa.geoscienceworld.org".Seismic surveying within the upper few meters of the Earth's shallow subsurface requires a high-frequency source. To ascertain the important features of such sources, experiments were conducted at test sites in central and eastern Kansas using various impulsive seismic sources (4.5-kg hammer, 30.06 rifle, and .22-caliber rifle) to examine the effects of minimizing source energy on the frequency content of reflection data. Results indicate that the higher energy near-surface seismic-reflection sources (e.g., sledgehammer, large-caliber projectiles) lack some of the high-frequency energy exhibited by smaller sources, precluding the detection of reflection signal from ultrashallow depths (<3 m) at the sites tested. At the test site in eastern Kansas, the .22-caliber rifle yielded more energy above 250 Hz than either the sledgehammer or 30.06 rifle. At the test site in central Kansas, where three reflective interfaces shallower than 3 m exist, the .22-caliber rifle with subsonic ammunition yielded the largest amount of energy at frequencies above 300 Hz and produced the best data
Varying the effective mass of geophones
This is the published version. Reuse is subject to the Society of Exploration Geophysicists terms of use and conditions.Traditionally, acquiring seismic data has rested on the assumption that geophone mass should be as small as possible. When Steeples and coworkers in 1999 planted 72 geophones automatically and simultaneously with a farm tillage implement, the effective mass of each of the geophones was significantly increased. We examined how the mass of a geophone affects changes in traveltime, amplitude, frequency, and overall data quality by placing various external masses on top of 100‐Hz vertical geophones. Circular barbell weights of 1.1‐, 11.3‐, and 22.7 kg; an 8.2‐kg bag of lead shot; and a 136‐kg stack of barbell weights were placed on top of geophones during data acquisition. In addition, a very large mass in the form of a truck was parked on top of two of the geophones. Four seismic sources supplying a broad range of energies were tested: a sledgehammer, a .22‐caliber rifle, a 30.06 rifle, and an 8‐gauge Betsy Seisgun. Spectral analysis revealed that the smaller weights had the greatest effects on the capacities of the geophones to replicate the earth’s motion. Consequently, using geophones with a large effective mass as part of an automatic geophone‐planting device would not necessarily be detrimental to the collection of high‐quality near‐surface seismic data
Near-surface common-midpoint seismic data recorded with automatically planted geophones
This is the publisher's version, also available electronically from "http://onlinelibrary.wiley.com".[1] We introduce the Autojuggie II as a device to speed the emplacement of geophones for near-surface seismic common-midpoint (CMP) surveys. Hydraulic cylinders force rigidly interconnected geophones into the ground simultaneously and automatically. We demonstrate that accurate CMP data can be recorded with geophones planted by this device, and that a CMP stacked section can be processed, from which reliable geologic information can be extracted. To make this demonstration, we compare the stacked section to a coincident and parallel section, whose data was acquired using conventionally hand-planted geophones. The two sections are very similar in amplitude, phase, and frequency. A slight difference in coherency exists in a ∼35-ms reflection; the stack corresponding to the automatically planted geophones shows better coherency relative to the comparison stack. However, the similarity of the sections indicates that accurate CMP data can be recorded using geophones planted by the Autojuggie II
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This is the publisher's version, also available electronically from "http://library.seg.org"