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

Abstract

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 laterally varying velocities. This is because walkaway seismograms are displayed by source-to-receiver offset, whereas neighboring traces do not correspond necessarily with neighboring raypaths or reflection points.