Isobel Whitcomb ‘17

Environmental Columnist

For people living in Southern California, the phrase “The Big One” refers to the fabled major earthquake for which Los Angeles is supposedly long overdue. It has become a part of common parlance. “The Big One” can take on a far fetched quality of local legend-- it’s referred to constantly in conversation and pop culture (I’m thinking of the recent flop of a film with Dwayne “The Rock” Johnson). However, it’s actually a very real possibility. Southern California residents were reminded of this fact on Wednesday, September 28, when a cluster of earthquakes took place in the Salton Sea area, near the town of Bombay Beach.

The day of the earthquake was warm. Everyone in the region received some kind of advisory. For students at the 5Cs, that would have come in the form of a text message or email. However, these advisories didn’t offer much detail in what exactly was going on beneath our feet. The email sent out by Campus Safety, referring to a small cluster of earthquakes in the Salton Sea area, mentioned an increased risk of a larger earthquake and reminded students what to do in the event of such a quake.

If your reaction to these texts and emails was anything like mine, you probably picked up your phone, shrugged, mentioned it in passing to the person you happened to be sitting with at the time, and promptly forgot about the warning (after all, it had just been earlier that week that we’d received a similar advisory about something as seemingly innocuous as dust).

However, some seismologists in the area were alarmed by the swarm of earthquakes. In the 24 hours after the first quake, around 200 more occurred. Only three quakes registered above 4.0 on the Richter scale-- a level at which most people resting indoors can feel the ground shaking. The swarm was concerning because of the risk of triggering a much larger earthquake. It turns out that the 200 or so miniquakes occurred along the Imperial Fault where it crosses the particularly volatile southern end of the San Andreas fault. According to seismologist Ken Hudnut’s 1989 hypothesis, when two faults intersect perpendicularly, clusters of small earthquakes in one fault can trigger a much larger earthquake in the connecting fault, especially when that fault is as large and volatile as the San Andreas. Consistent with this hypothesis, risk of a major earthquake (magnitude 7.0 or greater) spiked suddenly in the aftermath of the Salton Sea’s swarm of quakes. In any given week in Southern California, there is about a 1/10,000 risk of an earthquake of this magnitude taking place. By the end of the week, this probability had gone up to 1/100. Luckily, this risk eventually subsided. By Monday, October 3, fault activity had returned to normal background noise and the threat of a major earthquake returned to normal.

In the aftermath of this scare many seismologists are warning people to stay prepared. Others however, advise us Southern Californians not to hold our breath. Although the 25 years the San Andreas has been “overdue” for a major earthquake may seem significant, in geological time, a quarter century is a blip. In all likelihood, “The Big One” is still a long time coming.