1. ERDC Knowledge Core
2. Pre - Engineer Research and Development Center (ERDC)
3. Geotechnical Laboratory - (4/16/1978 - 2/22/2001)
4. Publication
5. Miscellaneous Paper

Title:	Use of shear waves in seismic refraction surveying
Authors:	United States. Assistant Secretary of the Army (R & D) Franklin, A. G. (Arley G.)
Keywords:	Compression waves Shear waves Refraction Subsurface exploration Seismic refraction Seismic waves Wave refraction Seismic surveys Wave velocity
Publisher:	Geotechnical Laboratory (U.S.) Engineer Research and Development Center (U.S.)
Series/Report no.:	Miscellaneous paper (U.S. Army Engineer Waterways Experiment Station) ; GL-79-17.
Description:	Miscellaneous Paper Abstract: The nearly universal practice in surface seismic refraction surveying for engineering purposes is to use only data obtained from compression waves, or P-waves, which are always the first arrivals and are thus the most easily detected and identified. Most seismic refraction surveys used in geotechnical practice are concerned with identifying depths to various layer boundaries or to the bedrock surface. P-wave velocities are normally obtained in the course of such surveys, but are usually of only secondary interest in seismic analyses. Shear wave, or S-wave, velocities, on the other hand, are of primary interest in engineering practice when they are needed for use as input to seismic analyses of structures. The S-wave velocity of the surface layer is frequently measured with a field survey using a layout similar to that of a refraction survey. However, refracted S-wave signals are not normally used. In principle, S-wave returns obtained by refraction through subsurface strata should be useful for measuring the S-wave velocities of these strata. In practice, however, results are often disappointing. In this report, the current state of the art in generating and discriminating refracted S-waves at the ground surface is described, and some theoretical and practical considerations in the propagation and discrimination of refracted S-waves are discussed. Theoretical considerations and experience indicate that horizontally polarized shear waves, or S𝚑-waves, are the best type of signal to use in S-wave refraction surveys. The S𝚑-wave is easier to distinguish from the P-wave than is the vertically polarized shear wave, or S𝚟-wave. Also, there is less energy lost through conversion to P-waves at interfaces between layers. Surface traction applied through hammer blows against a plank has proved to be a good source of S𝚑-wave energy. Phase reversal in the S𝚑-wave with reversal of the impulse direction in the source may be useful in discriminating S𝚑-waves. By superimposing and comparing signals obtained with reversed directions of impulse, or with a signal enhancement seismograph and alternating reversal of both source motion and geophone polarity, the S𝚑-wave can be enhanced while both the P-wave and the noise components are suppressed. Examples are shown of field data obtained by both of these methods. The studies described show that it is feasible to use refracted S-waves for the investigation of subsurface strata, at least to limited depths and under favorable conditions. The most serious limitation in the present state of the art appears to be that currently available S-wave sources are severely limited in the strength of the S-wave signal that they can apply. This limitation imposes limits on the length of the line over which a signal can be detected and therefore on the effective depth of investigation.
Rights:	Approved for public release; distribution is unlimited.
URI:	http://hdl.handle.net/11681/10179
Appears in Collections:	Miscellaneous Paper