SHEAR‐WAVE RECORDING USING CONTINUOUS SIGNAL METHODS PART II—LATER EXPERIMENTATION

Abstract

The emphasis in this shear‐wave research was placed on determining the general quality of data which could be obtained in different areas and whether such quality was consistent with the main objective of getting information from the shear‐wave data which could not be obtained from the corresponding P‐wave data. Borehole data are presented to show that the SH source of vibrations generates a downward‐propagating, horizontally polarized shear wave. Shear velocities were determined for depth intervals of two to three hundred feet, but no absolute correlation between [Formula: see text] and lithology could be established. In the deeper sedimentary section, [Formula: see text] averages about one‐half; but in the low velocity, or weathering layer, the ratio may be as small as one sixth. All the reflection record problems which arise from wave propagation phenomena in the LVL are generally much worse for SH waves than for P waves because of the very small SH velocities in the LVL. Nevertheless, by using large source and receiver patterns and various processing techniques, interpretable SH reflection records were obtained in almost every test area. It has been possible to obtain a depth of penetration about equal to that of the corresponding P‐wave records, with some reservations. The relative quality to be obtained has proved unpredictable. Several examples of SH reflection sections are presented with the corresponding P reflection sections. Some of these field examples show definite differences between the corresponding P and SH reflection sections. Such differences represent new information which potentially can be useful to the exploration geophysicist.