Secondary Shear Waves From Source Boreholes
Name
1991.7 Meredith et al.pdf
Size
483.89 KB
Format
Adobe PDF
Checksum (MD5)
ea34a2c9cd8ce349995c9c5f19aa56ad
Author(s)
Meredith, J . A.
Cheng, C. H.
Toksoz, M. N.
Date Issued
1991
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1991-07
Abstract
The purpose of this paper is to synthesize the most important results of the thesis work
of Meredith (1990) concerning radiation from seismic sources in boreholes.
Previous studies of radiation from sources in boreholes have been far-field studies
and have neglected the explicit contribution of the borehole. In general, this is fine for P-wave radiation and for S-wave radiation into high velocity rocks. However, tube waves "leak" shear conical waves (Mach waves) which propagate when the tube wave velocity
is greater than the shear wave velocity of the surrounding medium. These Mach waves
are of high amplitude because of the dominance of the tube wave and radiate away from
the borehole in a fixed conical shape. The shape of the cone is dependent on the shear
wave velocity of the medium and the tube wave velocity.
This paper defines the conditions under which these Mach waves exist and thoroughly
describes them in a physical sense and less so in a mathematical sense. Finally,
the relationship of Mach waves to data sets is examined and how Mach waves may be
confused with receiver borehole tube waves. To keep the presentation simple, radiation
from axial or torsional sources or radiation from empty boreholes is omitted in this
paper but fully addressed in Meredith (1990).
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