150186, RE: England is getting a taste of California|
Posted by Shelly, Thu Feb-28-08 03:29 PM
There is no known way to accurately predict an immanent earthquake more than a few days in advance at best. What is being predicted is that California is overdue for a major disastrous quake because the geological record shows that there has been one at fairly regular intervals over the last several thousand years. Since the last catastrophic quake was the San Francisco quake in 1906 at an estimated Richter magnitude of 7.8 (possibly as high as 8.3).
Quakes of this magnitude occur at roughly 200 year intervals, but lessor quakes that can cause major damage happen more frequently. the possibility of a quake in that region in the range of Richter 6.3 is predicted by the USGS with a probability of 70% +/-10% by 2030. This is based upon the stresses built up in two of the many fault lines running through the bay area, mainly the San Andreas, which requires a north/south slippage of about 20 feet to build up enough strain for a major quake. It's not nice to laugh at mother nature, nor is it wise to sneer at the USGS predictions.
The Richter scale measures the strength of an earthquake. It is a logarithmic value. An increase of one unit of magnitude such as from 3.8 to 4.8, represents a 10-fold increase in wave amplitude on a seismograph (about a 30-fold increase in the energy released). A magnitude 5.8 earthquake releases over 900 times the energy of a 3.8 earthquake. Of course how much damage results depends on how much a the location of a quake is built up and populated.