San Andreas Earthquakes May Be Triggered By The Pull Of The Sun And The Moon

A false-color image of the San Andreas Fault, seen here running through the Crystal Springs Reservoir. NASA/JPL-Caltech

These earthquakes register at no more than 1.0 on the moment magnitude scale, and anything around this value cannot be felt by humans – especially not 30 kilometers (19 miles) underground, the depth these lunar-induced tremors are occurring.

The San Andreas Fault is, overall, constantly moving, but segments of it have remained almost completely motionless for over a century, meaning that it’s been storing stress for an incredibly long period of time. When the fault does significantly rupture – something people refer to as the “Big One” – there will be many casualties, chaos, and a veritable catastrophe.

So by themselves, these quakes are completely harmless, but is their continued presence a good or bad thing?

Ultimately, it's probably not great. Although it seems like releasing small amounts of stress could help out in the long run, these earthquakes are so weak that they would either not make a difference at all, or they could end up triggering a major event.

In any case, these fortnightly cycles reveal fairly precisely where the fault is rupturing. It appears that whenever the deep part of the fault slips, the stress is transferred to the shallower part. This transferal takes time, so by knowing the rate at which stress is accumulating on the deeper fault, scientists may in the future be able to predict when the far more dangerous shallower section may rupture.


Aerial photograph of the San Andreas Fault in the Carrizo Plain Ikluft/Wikimedia Commons; GFDL

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