Another Reason For California To Be Scared: Earthquake Storms

Worrying about the Big One is so passé. What you should really be worried about are the Big ONES. Yep: chances are, it won’t be a single large earthquake that takes California out, it will be multiple, large earthquakes. Or perhaps you’d prefer to use the official Sharknado-esque term: “earthquake storms.”



This is the terrifying reality outlined in the new book Earthquake Storms: An Unauthorised Biography of the San Andreas Fault by John Dvorak, that’s been excerpted over at Salon.

Here is a plot befitting a Michael Bay movie in development: A quake on the San Andreas Fault could trigger a domino-like effect that will unleash the power of SEVERAL MORE EARTHQUAKES on SEVERAL DIFFERENT FAULTS as multiple paths of destruction ripple their way toward dozens of densely populated metropolitan areas.

Help.

A half-century ago, it was Stanford professor Amos Nur who first noticed the evidence of a phenomenon he called “stress transfer” when studying ancient earthquakes. Here’s one way Dvorak says to visualise it:

Imagine that a giant zipper is holding together two tectonic plates. As the two plates tug against each other, a segment of the zipper suddenly slides open, but, as a zipper is apt to do, it snags occasionally. As the tugging continues, the zipper again slides, then snags again. Each time, the sliding zipper represents an earthquake and the tugging of the plates becomes concentrated at another place along the zipper.



Or consider another example — one that Nur prefers. Take a wide rubber band and cut a few short slits in it. As the band is stretched, each slit in turn opens up and the ends of the slits lengthen. The sequence that the slits open and by how much depends on how the stress pattern gets transferred and concentrated at new locations across the rubber band.

Instead of the single, catastrophic event followed by the period of relative stability that we usually think of when our tectonic plates let off some steam, Nur started looking for evidence of series of earthquakes travelling along a fault over a period of decades. He first found it in the ancient city of Mycenae, where this kind of earthquake storm might have been responsible for the abandonment of several Mediterranean societies, triggering the end of the Bronze Age.

There was even more contemporary evidence in Turkey: a series of seven earthquakes erupting one after another along a 600-mile-long segment of the North Anatolian Fault:

In 1939, after two centuries of quiescence, the North Anatolian Fault, which runs across northern Turkey roughly parallel to the coastline of the Black Sea and which is a boundary between the African and Eurasian plates, came to life. By 1999, 13 major earthquakes had occurred. What is even more remarkable, 7 of the 13 ruptured the North Anatolian Fault in a systematic way: Each successive earthquake ruptured a segment of the fault that was immediately west of the previous earthquake.

Nur saw the same types of patterns in Italy and China: Seismic activity released along a network of faults, over time. But there’s one area that is currently of most concern to seismologists when it comes to potential earthquake storms. Due to both the size and the geography of California’s San Andreas Fault — which is widely considered to be the most overdue for some serious slippage — a single earthquake on that one fault could actually start a chain-reaction of devastation up and down the coast:

In particular, in southern California, the Cucamonga Fault, which runs west from Cajon Pass and along the southern base of the San Gabriel Mountains, could rupture simultaneously with or soon after a major earthquake along the San Andreas Fault. And that would lead to stress changes along the Raymond Fault — which is at the western end of the Cucamonga Fault — and from that to other faults in the Los Angeles region. In northern California, the Calaveras Fault splits off the main strand of the San Andreas just south of San Juan Bautista. So a rupture of the northern San Andreas Fault could lead to a rupture of the Calaveras — or the Hayward or the Greenville or the San Gregorio Fault. All this is to emphasise an important point: The exact sequence of future ruptures, and hence major earthquakes, along the San Andreas and its many adjacent faults cannot be predicted — which is why Jordan and others issued probabilities in their reports. The series of quakes would not disseminate out in a necessarily coherent direction. But one thing is certain: The last 100 years in California — which happen to correspond to a period of rapid urban growth — have been a period of seismic calm. That cannot continue.

The idea of stress transfer makes sense — of course earthquakes could trigger other quakes since they, like, move the earth — but these theories could change the way we can think about safety. The idea that it likely won’t be the San Andreas that will cause the most damage, but a “local” fault in your own neighbourhood, could help create awareness and change development.

I imagine something like a city-wide campaign to get to know your nearest fault and learn how it might react. Plus, exploring the behaviour of earthquake storms could aid us in one possibly helpful way: It could help cities see patterns and try to predict (somewhat) where and when more earthquakes are coming.

The entire story is fascinating and makes me want to pick up the book — not to mention double the size of my earthquake preparedness kit. [Salon]