San Andreas So Stressed That Earthquake Could occur Of Magnitude 8
San Andreas Fault So Stressed, Next Quake Could Be Magnitude 8
© 2006 by Linda Moulton Howe
"What’s the probability that we’re going to have a large earthquake, magnitude 6, 7 or 8,
on the southern part of the San Andreas Fault? There is about a 70% likelihood of a large
earthquake within the next 30 years." - Seismologist Debi Kilb, Ph.D.
July 27, 2006 La Jolla, California - Last month, the June 22, 2006, issue of the science journal Nature, published recent detailed research of the San Andreas and San Jacinto faults in Southern California. The data shows the San Andreas so stressed that its next quake release of energy could be a magnitude 8 on the Richter scale. The San Andreas Fault is considered the main boundary between the Pacific and North American tectonic plates that are slowly moving past each other. Some day in the far distant future, those moving plates might even break off sections of the Pacific coast into the ocean. The tension between those moving plates is what makes California "earthquake country."
[ Editor's Note: USGS reports that earthquake magnitude "is a measure of the size of an earthquake. The Richter Scale, named after Charles F. Richter of the California Institute of Technology, is the best known scale for the measuring of magnitude (M) of earthquakes. The scale is logarithmic; a recording of 7, for example, signifies a disturbance with ground motion 10 times as large as a recording of 6. The energy released by an earthquake of M 7, however, is approximately 30 times that released by an earthquake of M 6; an earthquake of M 8 releases 900 times (30x30) the energy of an earthquake of M 6. An earthquake of magnitude 2 is the smallest earthquake normally felt by humans. Earthquakes with a Richter value of 5 or higher are potentially damaging. Some of the world's largest recorded earthquakes--on January 31, 1906, off the coast of Colombia and Ecuador, and on March 2, 1933, off the east coast of Honshu, Japan--had magnitudes of 8.9 on this scale, which is open ended.
"As the Richter scale does not adequately differentiate between the largest earthquakes, a new "moment magnitude" scale is being used by seismologists to provide a better measure. On the moment magnitude scale, the San Francisco earthquake is estimated at magnitude 7.7 compared to an estimated Richter magnitude of 8.3.
"Intensity is a measure of the strength of shaking experienced in an earthquake. The Modified Mercalli Scale represents the local effect or damage caused by an earthquake; the "intensity" reported at different points generally decreases away from the earthquake epicenter. The intensity range, from I - XII, is expressed in Roman numerals. For example, an earthquake of intensity II barely would be felt by people favorably situated, while intensity X would produce heavy damage, especially to unreinforced masonry. Local geologic conditions strongly influence the intensity of an earthquake. Commonly, sites on soft ground or alluvium have intensities 2 to 3 units higher than sites on bedrock."]