Re: what is the piezoelectric effect seen during an earthquake

The effect is the same as you have been reading about, just on a larger 
scale.  Many natural and synthetic crystals will generate electrical 
charges when compressed and also when stress is released.  This includes 
quartz, the crystal used in many watches, which is a major part of 
many rocks within the earth's crust.  Prior to an earthquake, rocks near a 
fault zone are slowly compressed.  The rocks chnage shape and store 
energy in the same way as a spring does when you compress it.  This is 
easy to understand if you think of chemical bonds as electromagnetic 
springs.  During an earthquake, this stored strain energy is rapidly 
released as the fault slips and the rocks return to their unstrained state. 

All rocks are made up of many small crystals linked together.  These 
crystals don't have the nice shapes of things you see in a rock shop or 
jeweler's display, but they are still crystalline (they have an ordered and 
repetitious internal chemical structure) and so they display the properties 
of crystals.  Some display piezoelectricity.  It makes sense that if enough 
crystals generate a little bit of electrical field, then it could add up to 
something measurable.  There would typically be between a million (10^6) 
and a billion (10^9) crystalline grains in a cubic meter of rock and a 
moderate to large earthquake might release strain from 10 to 100 cubic 
_kilometers_ of rock.  

The big excitement in this area has been caused by measurements of low 
frequency electronic signals a few hours before the Loma Prieta earthquake 
in California in 1989.  Despte repeated attempts, attempts to detect 
similar signals have not produced reliable predictions.

I found some interesting abstracts by M. Ikeya who is looking at various 
electromagnetic effects of piezoelectricity associated with earthquakes.
 http://pumice.ess.sci.osaka-u.ac.jp/eqabst.html

He suggests that electrical discharges could account for a number of 
different phenomena reported around earthquakes.  Although he appears to 
have done some calculations of the strength of possible electric fields and 
have used artificially-produced fields to replicate reported phenomena, he 
does not have any data on actual fields during quakes (which would be 
difficult to obtain).  The abstracts on this web site were published in 
reputable, peer-reviewed journals.

This topic also seems to have attracted a significant psuedoscientific 
following.  The following webpage is a good example of how a little 
knowledge can be a dangerous thing: http://www.teleport.com/~bfryer/index.shtml
Fryer seems to assert that techniques that allow detection of quakes have 
been somehow supressed.  Since there would be major fame and a lifetime of 
major grant funding to be assured to whoever found a _reproducable_ method 
of 
earthquake prediction, and since most scientists are heavily ego-involved 
in their work, the suppression of valid research results among University 
researchers is not a credible hypothesis, though such conspiracy theories 
seem to be quite attractive to people.  In addition, Fryer, happily uses 
pieces of physical law and pieces of evidence that support his notion and 
just as happily ignores as much or more physics and data that do not 
support his ideas.  His most important data rest on the observations of one 
or two specially "sensitive" people.  It doesn't make the reports of those 
people invalid, but if the phenomenon is not reproducable or at least 
veifiable by others, then _by definition_ it is not science.  There may be 
people who can detect quakes, but the way to assess that is not by 
after-the-fact annecdotal reports.  It's by having those folks give 
before-the-fact predictions and then testing those predictions 
statistically to see if they are any better than random.  None of Fryer's 
work is published in the peer-reviewed literature.

Hope this helps,
Dave Smith, Geology and Environmental Science
La Salle University, Philadelphia, PA