If anyone here has some good information on those slow earthquakes that can occur over days or weeks, let me know! I will include some information that I found below that was in the LA Times back in 1996. I also read about the slow event here in Puget Sound in the summer of 1999, but if anyone else knows of an informative source it would be appreciated. Thanks!

SOURCE: Robert Lee Holtz, Times Science Writer, LA Times, 9/5/96, Copyright Los
Angeles Times --As posted by Joanne Pavia, Internet:bhps27a@prodigy.com--Posted on
9/6/96 on Prodigy Science & Environment BB--Topic: Obervations!!!

From the LA Times, 9/5/96: Discovery of Slow Quakes Stirs Scientific Tremors,
Earth: Some experts think the events, which can last for days, cause new temblors. Others say they're safety valves. By Robert Lee Hotz, Times Science Writer

Most people think of an earthquake as a fearsome release of earth energy measured in
seconds--still long enough at its most severe to topple the tallest buildings or remake a
mountain range. But in research made public Wednesday, scientists at the Carnegie Institution of Washington show how some earthquakes can last hours, even days. Indeed, they present evidence of a magnitude 4.8 earthquake along the San Andreas fault in 1992 that lasted a week--unnoticed by the people who live along the famous fault line.

The earthquake, which occurred near San Juan Bautista in Central California, was a hundred
times slower than any previously detected--so slow that it did not even generate conventional
seismic waves. The idea of a slow earthquake is a contradiction in terms --like jumbo shrimp.
And the significance of this newly discovered phenomenon already is being debated. Some
scientists suspect that this kind of slow-motion underground turmoil actually may trigger the
chain of events that leads to more conventional--and destructive--earthquakes.

Other experts, however, suggest the opposite: Slow earthquakes may prevent large temblors
by harmlessly venting the powerful forces that build up as the Earth's massive tectonic plates
grind against or slide underneath one another. In areas like Southern California and Japan,
experts warn of an earthquake "deficit" because there have been too few temblors to relieve
the pent-up seismic strain generated by plate motion.

Quake researchers and emergency planning officials have argued over whether Southern
California should brace itself for a series of devastating major earthquakes in the next few
decades, which would release the titanic energy building up in faults crisscrossing the region.
But the new finding suggests to some that perceptible, slow earthquakes may be a previously
unsuspected safety valve.

"It is a very interesting finding that has an important implication," said Hanoo Kanamori,
director of Caltech's seismological laboratory. "It shows there is a place in the crust where
slippage can be slow" and Earth's potentially destructive energy can be released safely.

Researchers have been tantalized for years by hints of such unusual earth tremors. A slow
earthquake was detected just before a 9.5-magnitude temblor in Chile in 1960. A second was detected after a magnitude 7 earthquake southwest of Tokyo in 1978. And traces of a third slow earthquake were recorded before a 1992 7.2-magnitude quake in Nicaragua.

But none of these were definitively linked to those larger quakes, nor were they as distinctive
or as slow as the San Andreas event reported in the current issue of the Journal Nature. The
slow quake near Tokyo lasted two hours and generated aftershocks as large as magnitude 5.8; the Nicaraguan event lasted three minutes--about three times longer than normal. Slow
earthquakes almost always elude detection, even with growing networks of sensitive
seismographs and satellite sensors. So scientists usually must infer them after the fact through more indirect means.

Researchers cannot use seismometers to detect them because such quakes usually do not
generate seismic waves. The ground movement at the surface is often so small that even
sophisticated measuring techniques, like the satellite-based Global Positioning System, can
miss it.

The slow earthquake on the San Andreas was detected serendipitously by two strain meters
that had been installed in bore holes near the fault in 1984. Scientists wanted to monitor an
area where the rocks on either side of the fault line often "creep" past each other without the
need of an earthquake to push them along.

In December 1992, the instruments picked up signals generated as 11 square miles of the fault surface slowly ruptured over a week to 10 days, the researchers reported in Nature. The sides of the fault moved about an inch, which would be equivalent to the movement caused by a magnitude 4.8 earthquake, the researchers said.

"We had never seen this sort of thing before," said Alan Linde, a staff scientist in the Carnegie Department of Terrestrial Magnetism, who conducted the study. "We observed these huge, slow changes [in the instrument readings]." Although the slow quake did not show up on seismographs, it did generate a series of more conventional aftershocks, ranging up to magnitude 3.7.

To double-check their readings, Linde and his colleagues monitored the site for three more
years. The temblor was much deeper and much more powerful than any known creep event,
putting it in a category all its own, the researchers said.