Direct-S wave modes produced by vertical and horizontal vibrators
Alkan, E. and Hardage, B.A., 2013. Direct-S wave modes produced by vertical and horizontal vibrators. Journal of Seismic Exploration, 22: 147-168. Horizontal vibrators are considered to be the optimal source for generating direct-S modes, which are S modes produced directly at a source station, not by mode conversion at interfaces remote from a source station. We show some results of a field test in which we investigated direct-S modes produced by vertical-force seismic sources. The test data were acquired by positioning horizontal vibrators and various vertical-force sources (vertical vibrator, vertical impact, shot-hole explosive) at the same source stations and recording their downgoing illuminating wavefields with a vertical array of 3-component geophones. In this paper, we compare only direct-S modes produced by vertical vibrators and horizontal vibrators. We show that there are strong similarities between the direct-S modes produced by these two sources. This investigation has considerable economic value because if it can be established that direct-S modes produced by vertical-force sources can be substituted for direct-S modes produced by horizontal vibrators, a large number of direct-S sources become available that can be used in any environment where P-wave seismic data are acquired.
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