Is The Moon Causing Earthquakes Along California's San Andreas Fault Line? State Rocked By Swarm Of Tremors

Coburn Palmer

The San Andreas Fault line has been rocking this week with small tremors being felt up and down Central California, but a new study suggests the moon's gravitational pull could be making things worse.

Seismologists and earthquake researchers have discovered the gravitational pull of the sun and moon affect the flexing of the Earth's crust the same way they create the ocean's tides.

The new study, published in the Proceedings of the National Academy of Sciences, found small quakes along the San Andreas Fault were more likely to occur during certain tidal phases, geophysicist Nicholas van der Elst told the LA Times.

"It's kind of crazy, right? That the moon, when it's pulling in the same direction that the fault is slipping, causes the fault to slip more – and faster."

"What it shows is that the fault is super weak – much weaker than we would expect – given that there's 20 miles of rock sitting on top of it."

"What it shows is that the fault is super weak – much weaker than we would expect – given that there's 20 miles of rock sitting on top of it."

From the Bay Area to the Central Valley, Central California residents have recorded a swarm of minor earthquakes, all with a magnitude of 3.7 or less, in the just the past few days and geologists have been unable to explain why.

Some seismologists have written off the swarm of activity as just a part of living along the San Andreas Fault in earthquake alley, but new research suggests the rise and fall of the oceans could be to blame.

The sun and moon work on the Earth's oceans to produce tidal flows, but they can also move rock and stone in the same way. Just as tidal strength increases and decreases over a two-week period, known as a fortnight, so does the force that compresses the Earth's crust, but less dramatically than the ocean. These low-frequency earthquakes show California's San Andreas Fault is almost constantly in motion, as David Shelly told Science Alert.

"We can use these low-frequency earthquakes as measurements of, at least in a relative sense, how much slip is happening at each little spot on the deep part of the fault where we see these events."

Researchers have discovered the San Andreas Fault is more likely to be affected by tidal forces during their lowest point or waxing period; not during the maximum peak when the pull of the sun and moon is strongest.

It was previously thought, the San Andreas Fault was immune to tidal forces because it's not situated in a way that would allow ocean currents to affect it, but the new study suggests there's a deeper level that's much weaker than previously thought.

"The springs on the San Andreas system have been wound very, very tight. And the southern San Andreas Fault, in particular, looks like it's locked, loaded and ready to go."

Photo by Cameron Spencer/Getty Images

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