Early Wednesday morning, a big earthquake shook several Italian towns and cities to the ground. At least 120 people are dead. It all happened in a region where seven years ago, another earthquake of similar magnitude shook several Italian cities to the ground, killing several hundred people. The latter earthquake became famous, not for the death and damage it caused, but for the trial that followed. Italy’s most prominent seismologists were taken to court, accused of recklessly addressing the public about the danger of a quake in the region–a week before the big one hit.
The L’Aquila earthquake became the most tangible proxy for a phenomenon that happens after every major quake: People–intelligent, educated, thoughtful–ponder questions like why didn’t science see this one coming? And that question is itself a concise way of saying that a lot of intelligent, educated, and thoughtful people don’t understand squat about earthquakes.
And I’m not being condescending here. I have written about quakes many times, and yet I still wound up Googling what seem to be some very basic questions. After the quake, my editors and I found ourselves asking each other all sorts of very basic questions. To wit: I legit had to Google whether there was a link between earthquake activity and Earth’s circadian patterns. So, with the help of some seismologists, here is WIRED’s guide to some common earthquake questions.
Can scientists predict earthquakes?
No, but they can forecast them. If that sounds like splitting hairs, think of it this way: Meteorologists know that during certain months of the year–say, summer–New York City is more likely to experience thunder storms. In fact, they can be pretty damn sure that during the fourth week of August, Manhattan will have at least one day of soggy weather. However, even up until the third week of August or later, it is pretty much impossible for them to say which day the sky will open up.
Like in meteorology, seismologists use a combination of historical records and sprawling computer programs to figure out their forecasts. “We use models of the whole Earth to think about how fast different plates are moving with respect to each other, so then we can say, ‘OK, over the long term we have an inch or so a year of movement and that will be concentrated on San Andreas fault or wherever,” says Simon Kemperer, a geophysicist at Stanford University. They compare these models to the historical record–not just the past 100 years or so, but 1,000, 10,000 years–to see the last time those faults released their strain.
But still, given all those computer models and such, why can’t they predict?
Right. So, scientists have those models, their historical data, and also some pretty good maps of where all the world’s fault lines lie. But in order to predict, you need to know the precise physical characteristics of the rocks making up those plates and faults. “If I take a wooden pencil in my hands and start to bend it, I know it’s going to break at some point in time,” says Kemperer. “But it is very hard to predict the exact millisecond when it will snap.” This is because, even though he knows the pencil is made out of cedar and graphite, he has no idea how the grain looks, whether the graphite is uniformly dense, if there’s any pre-existing stress on the pencil, and so on.
This gets way trickier with rocks. Even though scientists have done a hell of a job mapping all the different rock types making up the Earth’s geology, they still don’t have super granular understanding of all those rocks’ specific properties.
Are you sure scientists can’t predict earthquakes?
OK, let’s assume you started funding seismology like it was, I dunno, the Apollo moon mission or the US Marine Corps. “It might be theoretically possible to build up enough knowledge to predict earthquakes,” says Kemperer. But that would take many, many geologists observing each fault zone for decades upon decades. “So it’s not a practical task in terms of the scale of human lives.”
Are earthquakes more likely to happen during the day or night?
The tides exert a very small effect on the shape of the planet, including rocks along fault lines. “They do change the stress a tiny amount,” says Kemperer, “but it’s nothing compared to the stress required to trigger the quake.” So while the time of day can certainly impact the devastation caused by an earthquake–daytime quakes can injure and kill more people as they’re out and about–it doesn’t make them more or less likely.
Can one big quake cause another?
Depends on the size of the quakes and the distances between them. For instance, in the time between when I was assigned this article and when you are reading it, a 6.8 magnitude quake struck Myanmar. Based on the geophysical properties of how earthquakes propagate energy through the Earth, it’s pretty much impossible for energy from the Italian quake to have propagated thousands of miles to trigger the quake in Myanmar.
If the timing between the two quakes seems too coincidental for you to hang up your tin hat, spend a few days watching the USGS’s earthquake map. Big quakes happen all the time, all over the world. You just don’t hear about all of them because they happen in places where no people live.
Do small earthquakes release pressure on a fault?
Before the 2009 L’Aquila earthquake, one of the Italian scientists who got in trouble said in an offhand way that the cluster of small quakes the region had been experiencing were probably evidence that the fault was letting off steam. This is not true. (That scientists was a hydrologist, not a seismologist. Also, his comments were taken slightly out of context.) “The key is to remember that what everyone uses the a logarithmic scale to measure earthquakes,” says Kemperer. Let’s say you have a magnitude 4 quake, which is preceded by a weak 1 magnitude quake. Even if a hundred teeny temblors struck, each would only be about 1/10,000 the intensity of the moderately big one. “That’s why the small earthquakes don’t matter very much in terms of relieving pressure,” says Kemperer.
So if it can’t predict anything, what is all this science good for?
In practical terms, seismology is useful primarily for informing earthquake-prone regions how to survive their fates. More succinctly: Building codes. “It’s humbling to a seismologist, but in the end, it’s the structural engineers who save lives,” says Kemperer.