Hipótesis De The Big One (Inglés)

Case Study: Hypothesis the Big One

The 'Big One' is a hypothetical earthquake of magnitude ~8 or greater that is expected to happen along the SAF (San Andreas Fault, United States). Such a quake will produce devastation to human civilization within about 50-100 miles of the SAF quake zone, especially in urban areas like Palm Springs, Los Angeles and San Francisco.

No one knows when The Big One ("BO") will happen because scientists cannot yet predict earthquakes with any precision. The 1906 San Francisco quake (mag ~7.8) and the 1857 Ft. Tejon quake (mag ~7.9) took place in northern and central California, respectively, and both were 'Big Ones'. Some scientists think the next BO will be in southern California. The SAF passes through LA's three main transportation, power, and utility corridors in southern California: I-10 in San Gorgonio (Banning) Pass, I-15 in Cajon Pass and I-5 in Tejon Pass. The San Francisco peninsula's water supply is contained in San Andreas Lake (!) and the Crystal Springs reservoirs, both squarely on the SAF. Earthquakes with magnitude 8.5 or greater can probably only happen in California north of Cape Mendocino where the Cascadia megathrust subduction zone lies, but they are extremely rare, occurring on average once every few hundred years.

Smaller but still devastating earthquakes can happen on other faults as well: San Jacinto fault in southern California and the Hayward fault in the San Francisco Bay area. Recent experience with the Northridge quake shows that smaller and sometimes unknown faults can be a problem; until the earthquake, we did not know about the Northridge fault because it is a blind thrust fault.

A former Los Angeles science teacher has a theory on when big earthquakes are more likely to occur. David Nabhan, who spent 20 years as a junior high instructor in South Central, believes the forces of gravity and where the sun and moon are could determine large temblors.

“The lunar and solar tides would be aligned to perhaps trigger quakes on fault lines that are ready to rupture,” he said. Nabhan points to some deadly quakes in Southern California’s past:

• In 1933, a magnitude-6.4 quake struck Long Beach at 5:54 p.m. at dusk. It was a full moon.

• In 1971, a 6.6-magnitude quake hit Sylmar at 6 a.m. at dawn. It was a full moon.

• In 1991, a 5.8-magnitude quake hit Sierra Madre at 7:43 a.m. at dawn. It was a full moon.

“All those quakes took place at dawn or dusk or at new or full moons,” Nabhan said.

Notably absent from Nabhan’s list were the Whittier Narrows quake and the Northridge quake. While they both happened in the early morning hours, it was not within 36 hours of a full or new moon.

U.S. Geological Survey seismologist Lucy Jones about predicting earthquakes.

“There’s a very slight correlation. Not enough to predict any earthquake out of it,” she said. “People try to make patterns out of anything that scares them. We haven’t found anything that looks different before a big earthquake than other times. We get enough people sending us predictions. The slug trail lady who used to go out in her driveway and map out the slug trails in the morning and use that to predict where the next earthquake was going to happen.”

Asked about earthquake weather, Jones said, “The reality is earthquakes happen 5 to 10 miles deep in the earth and surface weather doesn’t affect anything at that depth.”

Asked what causes a quake to start and stop, she said, “I don’t know. We have figured out that earthquakes are happening at much lower stresses, and now we’re trying to understand the mechanisms that let them happen.”

Jones is the new science advisor to Mayor Eric Garcetti and her priority is to develop earthquake preparedness recommendations

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