Why Geologists are so Concerned with the San Andreas Fault

The San Andreas fault traverses the Western edge of California, beginning at the Mexican border, easing toward the West, and ending at Eureka, CA. This monster has been the source of absolute concern, as it transects two of the world’s megalopolises: the Bay Area complex, and the Los Angeles complex. The following catastrophic earthquakes: the 1906, 1957, and Loma Prieta earthquakes in San Francisco; the 1857 and Northridge quakes in Los Angeles; and dire predictions about a fault that has not had a major adjustment in locked segments in well over 150 years, which is the cycle of major quakes on that fault.

A 7.8 magnitude quake on a strike slip fault will direct the energy of the jolt in one direction. Placing both hands together, then sliding one hand forward demonstrates that action on a strike slip fault.  The energy from the quake will hit densely built up and  populated areas, such as Los Angeles or the San Francisco Bay Area to cause untold damage and death for massive numbers of people.

Nothing is immune or protectable from an earthquake, not freeways, military installations, living things, hospitals, or infrastructure. The good news is that California is notorious for excessive building code requirements that involve withstanding a large magnitude quake, but there will still be severe catastrophe from being in areas where there are no protections or predictions that work.

The deep tremors that occur along locked segments of major fault segments, such as the Parkfield, Ca, Japanese, and Cascadia segments occur deep in the earth’s crust, at about 30 miles underground. Earthquakes occur at a shallow point of 15 miles or less. There are subduction faults, where one tectonic plate is sliding under another and these movements can affect faults that are an ocean away. The San Andreas fault, a strike slip fault also has deep tremors going on, particularly at Parkfield. At one point, the San Andreas fault has several feet of differential between the surface and deep in the earth and the differential may correct, sending the released energy directly toward the Los Angeles urban complex.

As a result, there is increasing concern over whether increasing seismic and volcanic activity, worldwide whether from correction in differential between the surface and deeper crust, effects of major volcanic activity, subduction of tectonic plates, and buildup in pressure at locked fault segments will signal or cause a major quake. It is possible for a major earthquake of 7.7 or higher in magnitude to occur in California at any time, with major consequences for one of the most densely populated and expensive places in the world.

Los Angeles

Science Daily