Enhancement of Tectonomagnetic Change Due to Non-Uniform Magnetization in the Earth's Crust
Two-Dimensional Case Studies
1990 年 42 巻 5 号 p. 607-619
詳細
1990 年 42 巻 5 号 p. 607-619
A general theory of piezomagnetism in a uniform medium leads to the conclusion that a 1-nT change in the geomagnetic total intensity represents a change of 1.8×10-5 in strain. Empirically, however, a much larger tectonomagnetic change ΔF in units of nT has been observed for a strain ε. The ΔF/ε ratio amounts to some 10-3 in actual cases in contrast to 0.6×10-4 as expected from the theory.
It is the aim of this paper to understand the reason why such a discrepancy takes place on the basis of non-uniform distribution of magnetic layers in the crust. For that purpose, the tectonomagnetic effect arising from an infinitely long cylinder, which is embedded in a semi-infinite medium and is subjected to internal hydrostatic pressure, is estimated for a number of models which represent non-regular distributions of magnetic layers.
It turns out that, unlike the uniform model, the magnetic field arising from stress-induced magnetization is enhanced at some portions on the earth's surface depending on magnetic layer configurations because of the lack of symmetry of magnetization.
Since the earth's crust is magnetically complicated, it is not unreasonable to expect tectonomagnetic changes of an appreciable order in favourable cases.
