Chapter 16 "Ring Of Fire"

Los Angeles, like the North Pacific Coast sits on top of a of active fault lines and these faults are interconnected in what is called, "The Ring of Fire." It is an area where large numbers of earthquakes and volcanic eruptions occur. About 90 percent of the worlds earthquakes occur around this ring and they are a direct result of plate tectonics.









In Southern California about 30 earthquake a day occur with most of of a magnitude 2.0 or less.The Richter Magnitude Scale, more commonly used by the media and the public, measures the magnitude of the earthquake. It is calculated logarithmically in which each unit of amplitude of earthquake waves is factored ten times larger than the previous reading. An earthquake measured at 8.0, for example, would be 10,000 times stronger than an earthquake measured at 4.0. Great earthquakes, such as the 1964 Good Friday earthquake in Alaska, have magnitudes of 8.0 or higher. On the average, one earthquake of such size occurs somewhere in the world each year. The Richter Scale has no upper limit. Recently, another scale called the moment magnitude scale has been devised for more precise study of great earthquakes.








The San Andreas fault is considered one of the most dangerous in Southern California, partly because it has been some time since it has moved and its southern section is capable of producing a temblor as large as magnitude 8.1. or greater. 























Earthquake experts consider 1994's destructive 6.7-magnitude Northridge quake, which occurred on a different fault, to be a medium-sized quake.
























There are over 60 known large faults in L.A. County with an untold number of blind  and smaller faults. 


















There is no such thing as “earthquake weather”. Statistically, there is an equal distribution of earthquakes in cold weather, hot weather, rainy weather, etc. Furthermore, there is no physical way that the weather could affect the forces several miles beneath the surface of the earth. The changes in barometric pressure in the atmosphere are very small compared to the forces in the crust, and the effect of the barometric pressure does not reach beneath the soil.

Los Angeles Star 1857

The earthquake of 1857 thought to be located on a section of the San Andreas fault near Fort Tejon estimated to be an 8.0 on the Richter  Scale happened before Southern California was widely populated, although there were some first person accounts and the Spanish language newspaper reported the following;  "As a result of the shaking, the current of the Kern River was turned upstream, and water ran four feet deep over its banks. The waters of Tulare Lake was thrown upon its shores, stranding fish miles from the original lake bed. The waters of the Mokelumne River were thrown upon its banks, reportedly leaving the bed dry in places. The Los Angeles River was reportedly flung out of its bed, too. Cracks appeared in the ground near San Bernadino and in the San Gabriel Valley. Some of the artesian wells in Santa Clara Valley ceased to flow, and others increased in output. New springs were formed near Santa Barbara and San Fernando. Ridges (moletracks) several meters wide and over a meter high were formed in several places."






Sources:


Los Angeles Geology
http://www.scvresources.com/geology/


USGS
http://earthquake.usgs.gov/earthquakes/recenteqscanv/FaultMaps/Los_Angeles.html


Fort Tejon Earthquake
http://www.rms.com/publications/1857_FortTejon_EQ.pdf