Friday, May 29, 2015

The History of San Andreas Fault and its relationship to the Cascadia subduction zone (which stretches from Vancouver Island to northern California)

YouTube Published on Feb 16, 2015
The San Andreas Fault is a continental transform fault that extends roughly 810 miles through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The fault divides into three segments, each with different characteristics and a different degree of earthquake risk, the most significant being the southern segment, which passes within about 35 miles of Los Angeles.
Recent studies of past earthquakes indicate that there is a relationship (correlation) in time between seismic events on the northern San Andreas Fault and the southern part of the Cascadia subduction zone (which stretches from Vancouver Island to northern California). The San Andreas Fault goes into the Pacific Ocean near San Francisco where it links up (underwater) with the Cascadia Subduction Zone, in northern California. Scientists believe quakes on the Cascadia subduction zone may have triggered most of the major quakes on the northern San Andreas within the past 3,000 years. The evidence also shows the rupture direction going from north to south in each of these time-correlated events. However the 1906 San Francisco earthquake seems to have been the exception to this correlation because the plate movement was moved mostly from south to north and it was not preceded by a major quake in the Cascadia zone.[11]
A study in 2006 concluded that the San Andreas fault has reached a sufficient stress level for the next "big one", or a M ≥ 7.0, to occur. It also concluded that the risk of a large earthquake may be increasing more rapidly than researchers had previously thought. The paper stated that, while the San Andreas Fault had experienced massive earthquakes in the central (1857) and northern (1906) segments, the southern section of the fault has not seen any similar rupture for at least 300 years. Such an event would result in substantial damage to Palm Springs and other cities in San Bernardino, Riverside and Imperial counties in California, and Mexicali municipality in Baja California. It would be felt throughout much of Southern California, including densely populated areas of San Bernardino, Los Angeles, Orange County, San Diego, Ensenada and Tijuana, Baja California, San Luis Rio Colorado in Sonora and Yuma, Arizona.
As both the public and scientific community continue to speculate on the size of the next earthquake to strike California, predicting major earthquakes with sufficient precision to warrant taking increased precautions has long been sought but remains elusive.[10] Nonetheless, the 2008 Uniform California Earthquake Rupture Forecast (UCERF) has estimated that the probability of an M ≥ 6.7 earthquake within the next 30 years on the northern and southern segments of the San Andreas fault is somewhere between 21% and 59%, respectively.
According to the new forecast, California has a 99.7% chance of having a magnitude 6.7 or larger earthquake during the next 30 years (see Figure 1). The likelihood of an even more powerful quake of magnitude 7.5 or greater in the next 30 years is 46%. Such a quake is more likely to occur in the southern half of the state (37% chance in 30 years) than in the northern half (15% chance in 30 years) (see Figure 2).

The probability of a magnitude 6.7 or larger earthquake over the next 30 years striking the greater Los Angeles area is 67%, and in the San Francisco Bay Area it is 63%, similar to previous Working Group on California Earthquake Probabilities | WGCEP estimates (see Figure 3). For the entire California region, the fault with the highest probability of generating at least one magnitude 6.7 quake or larger is the southern San Andreas (59% in the next 30 years; see Figure 4). For northern California, the most likely source of such earthquakes is the Hayward-Rodgers Creek Fault (31% in the next 30 years). Events of this size can be deadly, as shown by the 1989 Loma Prieta earthquake (magnitude 6.9) and 1994 Northridge earthquake (magnitude 6.7).
Earthquake probabilities for many parts of the state are similar to those in previous studies, but the new probabilities calculated for the Elsinore and San Jacinto Faults in southern California are about half those previously determined. For the far northwestern part of the State, a major source of earthquakes is the offshore 750-mile-long Cascadia Subduction Zone, the southern part of which extends about 150 miles into California. For the next 30 years there is a 10% probability of a magnitude 8 to 9 quake somewhere along that zone. Such quakes occur about once every 500 years on average.
The full UCERF3 model and reports are now available.

Please also review my prior posting:
Monster Quake/Tsunami Are We Next? - From British Columbia's Knowledge Network

Since 2013, I now do my personal photographic and videographic work in Hi-Definition HD - 1080p. Many of my followers, however, do not have an Hi Speed Internet connection and the images may be pixilated – see also Wikipedia example. Or, rasterised (blurry).  There are a few ways of overcoming the problem.
Both the governments of Alberta and British Columbia have made commitments to place Hi Speed Internet throught-out their respective provinces; as is the case in most all of the other North American jurisdictions.

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