April 22, 2013 – The “Big One” May Hit Southern California Sooner than many Project: The information in the first three paragraphs, below, was gleamed from a research paper published by the Geological Society of America and presented to me by the author of the outstanding “AbreaveHeart1” Blog. The last two paragraphs are mine.
Shown, above, is a Tectonic map of the Pacific–North America plate boundary of the Gulf of California–Salton Sea trough region: The thin black lines are transform (strike-slip) faults; while the red lines are spreading centers in the southern Gulf of California and complex pull-apart basins in the northern Gulf of California and Salton trough. Abbreviations from north to south are: SAF—San Andreas Fault; G—Guaymas spreading center; C—Carmen spreading center; F—Farallon spreading center; P—Pescadero spreading center; A—Alarcón spreading center; T-A F.Z.—Tosco-Abreajos fault zone; EPR—East Pacific Rise. Normally, faults on the Baja California peninsula and islands are young, active and fragile.
The extreme southern end of the San Andreas Fault is more complex than initial measurements postulated. It is composed of spreading divergent faults (the red lines) and a series of transform or strike-slip faults (the black lines). Additionally, the North American Plate is composed of a harder granite material; while the Pacific Plate is more brittle and easily ruptured. Additionally, this area is composed of: (1) A zone of hot weak rock, (2) Rapid plate motion and (3) A complex oblique plate with a major zone of multiple strict-slip faulting.
In summary, the oblique spreading fault lines; from the Salton Sea in California to south of Baja California, Mexico; are moving faster than first hypothesized. Further, both the spreading and strike-slip faults are composed of hot weak rock, which is more susceptible to rupture. Both San Diego and Los Angeles are situated on very porous weak rock that is highly susceptible to rupture and significant structure failure.
Looking at the history of large earthquakes in California does not bode well for the future of this region. Over the last 155 years, California has seen seven earthquakes greater than Magnitude (M) 7.0 as follows: (1) Fort Tejon, 7.9M – 1857, (2) Owens Valley, 7.8M – 1872, (3) Imperial Valley, 7.8M – 1892, (4) San Francisco, 7.7M – 1906, (5) Lompoc, 7.3M – 1927, (6) Kern County, 7.5M – 1952, and (7) Landers, 7.6M – 1992. What jumps out from this list is that the really large quakes were all in the 1800’s and major California earthquakes are on a 22 ½ year cycle; 19 years if you remove the Landers quake. That projects the next powerful California earthquake from between 2013 and 2015 – with a mean year of 2013.
Because the trend line of the magnitudes of the quakes has been decreasing over the last 155 years, I would expect the next major California quake to be 7.8M to 8.2M. There are approximately 30 million people living along or near the coast of California. A simultaneous slip of the entire San Andreas Fault would be an apocalyptic event of unimaginable devastation.
The Master of Disaster