Main Article Content
signals. New magnetic dipoles, which vary with stress changes from mechanical sources, are produced
on the walls of the borehole. We evaluate such an effect quantitatively. First we formulate a general expression
for the borehole effect due to any arbitrary source models. This is valid everywhere above the ground surface as
well as within the cylindrical hole. A first-order approximate solution is given by a line of horizontal dipoles and
vertical quadrupoles along the central axis of the borehole, which is valid above the ground surface and a slightly
away (several tens of cm) from the top of the borehole. Selecting the Mogi model as an example, we numerically
evaluated the borehole effect. It turned out that the vertical quadrupoles produce two orders of magnitude
more intense magnetic field than the horizontal dipoles. The borehole effect is very local, i.e. detectable only
within a few m from its outlet, since it is of the same order or more than the case without a borehole. However,
magnetic lines of force cannot reach the ground surface from a deeper portion (>10 m) of a borehole.
No Permission Required
Istituto Nazionale di Geofisica e Vulcanologia applies the Creative Commons Attribution License (CCAL) to all works we publish.
Under the CCAL, authors retain ownership of the copyright for their article, but authors allow anyone to download, reuse, reprint, modify, distribute, so long as the original authors and source are cited. No permission is required from the authors or the publishers.