As Charles Richter, who pioneered earthquake measuring devices, once cautioned: “When you get a lot of earthquakes, you get a lot of earthquakes.”
Q: Scientists weren't just wrong about earthquakes in the centuries leading up to the 1906 San Francisco quake. They were really wrong. What did they believe?
A: If you go back to the Enlightenment, they thought they were related to chemical explosions. By the 19th century, many scientists said they were caused by large volcanic explosions happening within the Earth. There was no wide acceptance of the idea that earthquakes were actually caused by the sliding of great crustal blocks against each other until the 1906 earthquake, which ruptured the earth's surface for almost 300 miles. The ground had actually slid tens of feet along that rupture.
Q: Earthquakes can happen when giant chunks of land relieve the pressure that builds as they press against each other. You write that this is akin to what happens to a railroad car when it's pushed. Could you explain that?
A: Imagine you're in a railroad car with the brakes on. It's getting pushed by another car, but it won't slide because of the brakes. Eventually, however, the friction is overcome and the wheels start to slide on the iron rails. This makes the whole car shudder. Another way to look at it is to put your hands palm down on a table and try to slide it. It only goes in little jerks.
Q: What is an "earthquake storm"?
A: During the last few decades, it has been realized that earthquakes do not occur randomly, nor do they occur like clockwork. Instead, earthquakes, even large ones, tend to cluster in time and space. An earthquake storm is when there is a cluster of large earthquakes in a region occur over a period of several decades. The best examples are the earthquakes that are now happening in northern Turkey along the North Anatolian fault. The storm began in 1939. Since then there have been 13 major earthquakes, and scientists expect at least one more major earthquake is yet to happen at the west end near Istanbul. So the Turkish government is trying to retrofit many buildings for the coming shaking as well as protect many of the art treasures in the city and much of the ancient architecture.
Q: How does California fit into the world of earthquake storms?
A: Most of the motion between the Pacific and North American plates occurs along coastal California. In the last hundred years, there has been only one significant earthquake along those plates: the 1989 Loma Prieta earthquake, also known as the World Series earthquake. But during the previous hundred years before that, there were five significant earthquakes along the California coast, in 1812, 1838, 1857, 1868, and 1906. Large earthquakes are the major means by which seismic energy gets released after building up between the two tectonic plates. And so, one or more large earthquakes are in California’s future, it is a matter of when?
A: The most crucial question to be answered is: What triggers a large earthquake? There are two opinions about this, and it is hotly debated by seismologists. One theory says all earthquakes begin the same. Small earthquakes are popping off all the time in California. If a large earthquake is just a small earthquake that grows to a huge size – say, by a cascade of many, many small earthquakes – then there is no hope that large earthquakes will ever be predicted. If so, we will never be able to do anything better than provide probabilities of future earthquakes. The other theory says the beginning of a large earthquake is fundamentally different from small earthquakes. If so, then large earthquakes might be predicted.
Q: Many Americans don't live in quake zones but may travel to them and encounter a quake. Other folks – like me! – live in quake areas but haven't kept up on the latest advice about what to do when a big one hits. Can you give us a quick refresher course in a sentence or two?
A: Stay put. Duck, Cover, and Hold on.
As someone who rode out last night's earthquake storm, I hope this was not the prelude to the even bigger earthquakes that Dvorak is expecting.