Stress-Induced Changes in the Electrical Conductivity of Igneous Rocks and the Generation of Ground Currents
Stress-Induced Changes in the Electrical Conductivity of Igneous Rocks and the Generation of Ground Currents
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DOI：
10.3319/tao.2004.15.3.437(ep
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发表时间：
2004-09
影响因子：
0.8
通讯作者：
F. Freund;A. Takeuchi;B. Lau;Rachel Post;J. Keefner;Josh Mellon;A. Al-Manaseer
中科院分区：
文献类型：
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作者：
F. Freund;A. Takeuchi;B. Lau;Rachel Post;J. Keefner;Josh Mellon;A. Al-Manaseer
如果我们希望了解地球在大地震前发出的非地震信号，我们需要了解岩石在增加的压力下的物理学。特别是我们需要了解地面电流的产生。我们已经开始研究火成岩的导电性在应力下如何变化，以及涉及到什么类型的电荷载流子。我们发现，石英丰富的花岗岩和无石英斜长岩都产生电子电荷载体时，受到应力。电荷载流子是空穴（p-空穴），即，氧负离子亚晶格上的缺陷电子。它们从受压的岩石体积（“震源体积”）向外扩散，进入周围的无应力岩石。时变地电流是产生震前局部磁场异常和低频电磁辐射所必需的。我们认为，应力引起的p-空穴电荷载流子的激活及其从源体积流出是地壳中产生地电流的基本过程。我们建议，到达地球表面的p-空穴导致的地面电位的变化，可能会引起电离层扰动。我们进一步提出，在地面上的高电场的建立，可以使空气，从而导致离子发射和电晕放电。当p-空穴在研磨表面重新结合时，预期它们形成振动高度激发的0-0键。这些0-0键的去激发将导致受激中红外发射，这可能解释卫星图像中所确定的地震前“热异常”。
If we can ever hope to understand the non-seismic signals that the Earth sends out before major earthquakes, we need to understand the physics of rocks under increased levels of stress. In particular we need to understand the generation of electrical currents in the ground. We have begun to study how electrical conductivity of igneous rocks changes under stress and what types of charge carriers are involved. We show that quartz-rich granite and quartz-free anorthosite both generate electronic charge carriers when subjected to stress. The charge carriers are positive holes (p-holes), i.e., defect electrons on the oxygen anion sublattice. They spread out of the stressed rock volume, the “source volume”, into the surrounding unstressed rocks. Time-varying ground currents are required to generate pre-earthquake local magnetic field anomalies and low-frequency electromagnetic emissions. We posit that stress-induced activation of p-hole charge carriers and their outflow from the source volume is the basic process by which ground currents can be generated in the Earth’s crust. We propose that the arrival of p-holes at the Earth’s surface leads to changes in the ground potential that may induce ionospheric perturbations. We further propose that the build-up of high electric fields at the ground surface can ionize the air, hence cause ion emission and corona discharges. When p-holes recombine at the ground surface, they are expected to form vibrationally highly excited 0-0 bonds. The de-excitation of these 0-0 bonds will lead to stimulated mid-IR emission, which may explain the reported pre-earthquake “thermal anomalies” identified in satellite images.