There's a third possible explanation ...
In the Journal of Scientific Exploration, Vol. 17, No. 1, pp. 37–71, 2003, there is an excellent report that addresses the more down-to-earth problems facing geophysicists trying to understand earthquakes. The paper is titled, Rocks That Crackle and Sparkle and Glow: Strange Pre-Earthquake Phenomena, by Dr. Friedemann T. Freund, a professor in the Department of Physics, San Jose State University, and a senior researcher at NASA Ames Research Center. Dr. Freund writes:
“Many strange phenomena precede large earthquakes. Some of them have been reported for centuries, even millennia. The list is long and diverse: bulging of the Earth’s surface, changing well water levels, ground-hugging fog, low frequency electromagnetic emission, earthquake lights from ridges and mountain tops, magnetic field anomalies up to 0.5% of the Earth’s dipole field, temperature anomalies by several degrees over wide areas as seen in satellite images, changes in the plasma density of the ionosphere, and strange animal behavior. Because it seems nearly impossible to imagine that such diverse phenomena could have a common physical cause, there is great confusion and even greater controversy.”
Freund outlines the basic problem:
“Based on the reported laboratory results of electrical measurements, no mechanism seemed to exist that could account for the generation of those large currents in the Earth’s crust, which are needed to explain the strong EM signals and magnetic anomalies that have been documented before some earthquakes. Unfortunately, when a set of observations cannot be explained within the framework of existing knowledge, the tendency is not to believe the observation. Therefore, a general malaise has taken root in the geophysical community when it comes to the many reported non-seismic and non-geodesic pre-earthquake phenomena. There seems to be no bona fide physical process by which electric currents of sufficient magnitude could be generated in crustal rocks.”
Freund makes an excellent attempt to explain all of the phenomena in terms of rock acting like a p-type semi-conducting material when placed under stress. Normally rock is a good insulator. For example, the emission of positive ions from the Earth’s surface may act as nuclei for the ground-hugging fog that sometimes occur prior to earthquake activity. And although the surface potential may only be in the 1–2-Volt range, the associated electric field across a thin surface layer can reach hundreds of thousands of volts per centimeter, enough to cause corona discharges, or “earthquake lights.” Thermal anomalies seen from space before an earthquake may be due to the emission of infra-red light where the semi-conductor charge recombines at the surface. Disturbed animal behavior may be due to the presence of positive ions in the air.
As Freund says, this theory places an explanation in the realm of semiconductor physics
Note that this inference subtly differs from those in the article, as a semiconductor inference is only meaningful if it relates to a current which is traveling from one conductor to another through an insulating layer. In this case, space and the Earth's core would be the conductors, and the Earth's surface layer would be semiconducting. So, it involves questioning the claim that space is electrically neutral -- and that turns out to be a very important question to ask.