Paul D. Vincent

Fixed-source and fixed-receiver walkaway seismic noise tests: A field comparison

Seismologists and geophysical literature often use the term “walkaway” to describe any survey used to analyze wavetrains based on source-to-receiver offset. A distinction should be made between receiver-group moveout (fixed-source walkaway) and source moveout (fixed-receiver walkaway) when multiple channels simultaneously record signal from multiple independent geophones. Three data sets are presented that illustrate this distinction: one collected in an area where a fixed-receiver walkaway survey recorded similar data and was more time efficient than a fixed-source walkaway survey, and two others collected in an area where dipping reflectors and laterally varying velocities caused the fixed-receiver walkaway data to be significantly different than the fixed-source walkaway data. The results show that, while still useful, clarity in recorded data is lost when fixed-receiver walkaway surveys are substituted for fixed-source walkaway surveys in areas with uneven surface topography, dipping interfaces, or la...

Combining near‐surface seismic reflection and ground‐penetrating radar data in the depth domain

Shallow seismic reflection (SSR) and ground-penetrating radar (GPR) data of approximately the same wavelength were collected over a coincident volume of geologic material in an effort to image the water table at a test site near Clay Center, KS. Although the top of the saturated zone was successfully imaged using both techniques, no significant reflectors were imaged above the water table using SSR or below the water table using GPR. The SSR and GPR data sets were depth converted and vertically stacked to provide a more complete image of the subsurface. Instead of having two different sections representing depths of ~0-5 m (GPR) and ~4-30 m (SSR), the combined section includes the near-surface stratigraphy, water table, and bedrock, among other geologic features. It is important to note, however, that this method of data combination is intended for qualitative purposes only because the two methods measure different physical properties of the subsurface and quantitative analysis of the vertically stacked section may lead to erroneous results.

Analysis of the Seismic Response of Rigidly Interconnected Geophones Attached to Steel Media of Various Shapes

Previous experiments have shown that seismic information can be recorded using rigidly interconnected geophones affixed to channel iron. The purpose of the experiment discussed here was to compare seismic data acquired using manually planted geophones to data gathered from geophones attached to steel media of various shapes and then planted hydraulically. The shape of the steel media to which the geophones were attached influenced the quality of the recorded seismic data. Of the five shapes tested, square tubing was found to be best for recording seismic information, as determined by the amplitude coherency of the target reflections, airwave damping, and noise content. Furthermore, the airwave observed on the test-line records for geophones affixed to the variously shaped steel media was less coherent than was the airwave on the control-line records for the manually planted geophones.

Effect of orientation of hollow‐bar‐mounted geophones on airwave coherency

Previous shallow seismic reflection work using geophones rigidly mounted to hollow steel tubing showed a significant reduction in airwave coherency compared to a control line of traditionally hand-planted geophones when used in 2-D walkaway surveys. This research shows that the reduction in airwave coherency is dependent on the azimuth of the source location in relation to the steel-tubing receiver array. Data recorded from shot locations along a line orthogonal to the steel-tubing orientation exhibited a larger amplitude airwave that remained coherent in the data for a longer period of time than when a traditional array of hand-planted geophones was used to record data. These experiments indicate a ~60° zone of airwave degradation off of both ends of the bar in which the coherency and amplitude of the recorded airwave are sharply reduced. For shots in the crossline direction, the airwave is shown to have more reverberation cycles; this adversely affects the signal-tonoise ratio. These findings may impact geophone array orientation for shallow 3-D seismic surveys using rigidly interconnected geophones.

Field testing hydraulically planted receivers fitted with custom‐made spikes

Field-testing ways to improve geophone-to-ground coupling is essential to refining techniques that will allow a broader bandwidth of seismic frequencies to be recorded. With the development of a hydraulically operated geophone-planting device, quickly and efficiently planting large numbers of closely spaced geophones equipped with longer spikes is now feasible. This experiment was conducted to determine the effects of geophone spike length on the timeand frequency-domain seismic data recorded using geophones rigidly attached to channel iron.