What is the dreaded San Andrés fault and why is it so disturbing

Whenever it trembles in California, the question is repeated: is "Big One" closer?

With him "Big One"They refer to a catastrophic earthquake that should have occurred, according to the seismologists.

Fears have come back to loose this week. A magnitude 7.1 earthquake rocked southern California on Friday night.

This earthquake was recorded only one day after magnitude 6.4 in the same region.

California is prone to earthquakes because it is located on a series of faults, that is, regions where the tectonic plates meet.

The most important of these – and potentially the most dangerous – is the San Andreas Fault, which crosses the state from north to south and stretches for 1,300 kilometers.

This week's earthquakes did not occur in this fault, but their proximity raises concerns.

The fault delineates the North American plate of the Pacific Plate and is one of the most studied on the planet because, in its practical totality, it is on the Earth's surface.

The huge urban centers of Los Angeles, the second most populated city in the United States, and San Diego, and the 38 million people living in its surroundings, are based there.

The central part of the fault erupted about 160 years ago and the northern part in 1906, causing the devastating 7.8-degree earthquake that destroyed much of San Francisco in 1906 and left more than 3,000 dead.

But what worries most scientists is the southern part of the fault, in which no earthquake has occurred for nearly 300 years, although the geological record indicates that it is the cause of a major earthquake of periodicity of about 150 years, and during all this time has accumulated tension.

The last major earthquake in this region dates back to 1700, but there are no details about what happened while there was no registration at that time.

At the 2016 National Earthquake Conference in California, participating scientists have already warned that the southern part of the San Andreas Fault was "loaded and ready" to cause a major earthquake.

Seismologists from the United States Geological Survey have simulated the effects of a major earthquake in California for a study program.

One of his computer models badumes that the next major event in the San Andreas Fault will be a magnitude of 7.8; It will trigger a break in southern California near the Salton Sea, and then head north along the can not hit Los Angeles.

The most conservative calculations suggest that if an earthquake of this magnitude were to occur in this section, about 2,000 people would die and more than 50,000 would be injured.

About 1% of buildings in an area of ​​10 million people would collapse and about half of the buildings in the area should be abandoned.

Property damage would exceed US $ 200 000 million.

The viability of communities after such an event depends on the preparation.

In California, much of the attention to planning has been reflected in building standards.

Following the earthquake in San Francisco, northern California, new regulations were introduced requiring the reinforcement of concrete structures, many of which house schools and hospitals.

In 2014, Los Angeles City Council proposed similar regulations.

Earlier this year, ShakeAlert LA began operating, an earthquake early warning system similar to that found in seismically active countries such as Japan or Mexico.

This is a mobile application that alerts residents of Los Angeles County up to 40 seconds before an earthquake of magnitude 5 or higher occurs. This not only alerts the public, but also the authorities.

For experts, the question is not whether the San Andreas Fault will break in Southern California, but when.

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