The Tug of Celestial Bodies Causes the Very Ground to Shake

Here's a novel explanation for California's earthquakes: Blame the sun and the moon. According to researchers at UC Berkeley, their combined gravity is just enough to set the San Andreas Fault in motion.

A few years ago, seismologists detected tremors in the San Andreas Fault at a depth where they didn't expect to find any — some fifteen miles underground. Now, they believe the explanation lies out in space. When the sun and the moon line up in the direction of the fault's break, their combined gravity drags enough water through subterranean channels that it triggers seismic activity.

Pressurized water lubricates the rock plates, Robert Nadeau of the Berkeley Seismological Laboratory explained to reporters, making it more likely that they'll shift position when water trapped underground responds to the call of extraplanetary gravity. The resulting tremors can go on for tens of minutes, although they're usually not very forceful, registering only on sensitive equipment.

Tremors are categorically different from earthquakes — they take place at a deeper level, and aren't necessarily felt on the surface. Roland Bürgmann, a UC Berkeley professor and co-author of the group's study in Nature this week, points out that while some San Andreas tremors definitely seem to be influenced by tides, there's no evidence yet of this type of movement translating into full-on earthquakes. But Nadeau adds,

It is certainly in the realm of reasonable conjecture that tremors are stressing the fault zone above it. The deep San Andreas Fault is moving faster when tremors are more active, presumably stressing the seismogenic zone, loading the fault a little bit faster. And that may have a relationship to stimulating earthquake activity.

Seismologists have historically tended to discount the idea that tides can influence earthquakes, so it's significant for Nadeau to acknowledge a possible link. Quake prediction is a notoriously tricky business, but if the forces at work in the San Andreas Fault become better known, it could allow people in California to anticipate seismic activity a bit more accurately. Beck sang about earthquake weather, but it seems like it's the earthquake moons that really demand a closer look.