Every few years or so, the world has to deal with one catastrophic earthquake, which, especially when it hits somewhere in the developing world, can result in massive loss of life and property. The most recent one was in Nepal, where the latest death has exceeded 5,000. What makes these earthquakes even more terrifying is the fact, even though we understand them pretty well and our data gathering and computational capabilities have increased a lot over the years, scientist still have basically no way of knowing exactly when the next big one will occur. So what makes earthquakes so difficult to predict?
First of all, we have to understand what causes an earthquake. Our planet’s crust, the relatively thin outermost layer of our planet which floats on top of the semi-molten mantle, is divided into several huge slabs of rock called tectonic plates, like the cracked shell of a boiled egg. These plates aren’t static – powerful currents within the mantle slowly move them around, at a rate of a few millimeters or centimeters per year. Huge tensions build up in the places where they meet (called plate boundaries) because as the plates move, the boundaries themselves stick, due to friction. Eventually, the rocks snap (or slip), and all that tension is released as seismic waves – this is what’s called the stick-slip process, and it’s what causes earthquakes.
Over the years, as our understanding of this phenomenon got better, we’ve been getting better at forecasting (not predicting!) earthquakes. It all started with recognizing that earthquakes are caused by faulting, the movement of rock along a break in the surface (a fault), and not, as previously thought, the other way around – the cracks in the earth were just a result of the earthquake. Today we know that most seismic events happen where tectonic plates collide head-on or slide along one another, which tells us where to expect them and where we should better prepare.
There are other things seismologists can do to try to actually determine when the next big one will happen. They can use historical and geological records to determine the intensity and frequency of past earthquakes. Also, they can improve the current models of what happens along the plates and roughly estimate the time and place where a big earthquake might occur. Once again, we’re talking about a forecast – scientists are basically saying an earthquake will occur sometime in the next couple of decades. And it’s highly unlikely they’ll ever be able to do better.
That’s because those earthquake-generating tectonic plates are huge, 100 km thick on average, and tremendously heavy. In order to predict when an earthquake will happen, you’d have to know precisely the weight, speed, and direction in which these massive slabs of rock are moving; you’d have to understand the underlying mechanism which makes them move; and you’d have to exactly what kind of rocks are they made of and what are their properties, so you know how much force is needed to break them. Also, keep in mind earthquakes happen dozens or hundreds of kilometers below the surface, so you’d need to gather all this data from extremely deep underground. It’s highly unlikely we’ll ever be able to do all of this.
While we can’t predict earthquakes in time to actually organize an evacuation or take other measures which require adequate advance warning, we could do other things to mitigate the damage. First of all, there are a number of simple things each and every one of us can do to make sure we are prepared in case of a disaster. Things like securing furniture or knowing where to take cover when the ground starts to shake (here’s a link with some of these tips, or watch the video below).
But perhaps the best thing we could do in order to reduce damage from seismic events would be to build earthquake-proof structures. Engineers in Japan and California have come up with intriguing ideas to reinforce buildings, making them better suited to withstand a powerful shock. And there are plenty of low-tech ways to improve houses in the developing world as well.
Probably the only thing we can tell for sure about future big earthquake is that we’ll never be able to tell exactly when it will hit. Nevertheless, seismologists do know where earthquakes are most likely to occur, and could maybe even set a time frame for the event. Knowing which places are at risk is a valuable piece of information in and of itself, and could be used to put in place various measures, thus greatly limiting the damage done by these natural disasters.