For decades, even centuries, people from around the world who live in seismically active areas have reported on strange phenomena days or hours before major earthquakes. These phenomena include changes in the near-ground atmosphere like fog and haze, changes higher up in the atmosphere like stationary clouds over the faults that will soon rupture, and unusual animal behavior. All these phenomena occur well before the earthquakes. They are of great interest as potential earthquake early warning signs.

Thousands of lives and probably billions of dollars could be saved, if the causes of these phenomena would be properly understood. Strategies could then be developed to use such pre-earthquake signals to take steps that can reduce the losses. However, before such strategies can be developed it is necessary to better understand how these pre-earthquake phenomena are generated and what they mean.

Many scientists in different countries have tried to find a cause or different causes for the different pre-earthquake signals that have been reported. Many suggestions have been made. Some may have explained this or that, but none led to an overarching understanding. Disappointed by this general failure, famous seismologists in the USA and other countries have declared publicly that earthquakes cannot be predicted.
They say pre-earthquake signals are a myth and it would be a waste of time (and money) to study them.

The situation has changed dramatically with the discovery that rocks contain dormant electronic charge carriers which can be awakened by stress. Stress is what the Earth applies generously to the rocks deep below, ever increasing levels of stress, up to the point where the rocks will rupture catastrophically leading to an earthquake.

The electronic charge carriers that are awakened in rock deep below have a special name: positive holes. They have some peculiar properties. Once activated, the positive holes can flow out of the stressed rock volume, travel through kilometers of rocks and all the way to the surface of the Earth. In 1984 Bruce King and I wrote a theoretical paper in one of the leading physical journals, the Physical Review. In this paper we showed that, when the positive holes arrive at the surface, they build up tiny but very steep electric fields, easily reaching five hundred thousand to a million volt per centimeter. Ever since this time I have been thinking that such steep electric fields should ionize the air. The process for doing so is well known to physicists: it is called "field ionization". It involves air molecules that come close enough to the rock surface to be subjected to these tiny but very steep electric fields. The air molecule then looses an electron to the rock surface and flies away as an airborne positive ion.

In the late 1990s I had the opportunity to test my ideas with a very powerful press at the Geophysical Laboratory of the Carnegie Institution in Washington, DC. Figure 1a shows a large block of a red granite weighing fifty kilograms or more sitting under the piston of a press that can deliver up to 1500 tons. When we applied a load to the center of the granite, it broke at around 300 tons into many pieces as shown in Figure 1b. However well before this breakage, I was able to measure ions streaming off the rock surface but well outside the place where the piston was pressing on the rock.

In the following years I was not able to continue this study, though Ipublished these preliminary results in 2003. Recently, together with mycoworkers Ipek Kulahci and Gary Cyr, we have been able to reproduce thesame result – massive ionization of air at the rock surface – by using apress at the NASA Ames Research Center in California that can deliver only 30 tons. Normally 30 tons are not enough to break a large chunk ofvery hard rock like granite or gabbro but by using a few tricks we were able to produce conditions where the air becomes massively ionized atthe rock surface. During application of thestresses, but before the large piece broke off, we measured how many ions were forming at the rock surface. To our delight we found thatevery square centimeter of the rock surface had been producing up to1,000,000,000 (one billion) ions per second.

What does this mean? Well, one billion ions forming per square centimeter surface per second and drifting up translates into large ion concentrations in the ambient air. Normally ion concentrations per cubic centimeter of air vary between about 100 and 10,000 depending on whether one is in a city or far away in nature, in a forest or on a lake. Much higher ion concentrations such as millions or hundreds of millions per cubic centimeter will have very distinct consequences. For one, every single airborne ion can act as a nucleus that attracts water molecules so that they condense into a tiny droplet. Millions and billions of tiny droplets make for a fog or haze. Then, depending upon the atmospheric conditions, another process can become important too: during condensation of water droplets heat is released. The heat warms the air and this may be enough to create a updraft that carries the water droplets high up. There, maybe a 1000 meters high, they can grow into
larger droplets and form clouds.

This is where the question of pre-earthquake phenomena comes back. If the build-up of dangerously high levels of stress deep below progresses along an earthquake fault, which is going to rupture in maybe a day or two, we can reasonably expect that large numbers of positive hole charge carriers will percolate upward from seismogenic depth to the surface of the Earth. There, over an area many kilometers wide along the trace of the fault, a situation may be reached where ionization of air molecules begins on a massive scale. Depending upon the overall weather conditions this massive formation of airborne ions can lead to fog, haze or clouds. Even if a slight wind blows, it is quite possible, even likely, that the fog, haze or clouds are not blown along. They will be stationary, remaining in place, because the surface of the Earth below, the area along the fault line, will continue to produce large numbers of airborne ions that replenish any cloud which the wind tries to blow away.

The same airborne ions may also have a noticeable effect on animals, which are surely much more sensitive than the average city-dwelling human being.

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Friedemann T. Freund
NASA Ames Research Center, MS 242-4
MOFFETT FIELD, CA 94035-1000
Tel (at NASA) 650 604-5183
Tel (at CSC) 650 810-0218
Cell 650 279-8478
Fax 650 604-4680
e-mail friedemann.t.freund@nasa.gov
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Department of Physics
San Jose State University
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Principal Investigator
Carl Sagan Center (CSC), SETI Institute