In a windowless side room of the Earth Simulation Laboratory in Utrecht, André Niemeijer (48) mimics earthquakes. In a container there are two pieces of white plastic with a layer of salt in between: a fracture with grainy fracture material, which is created as rocks along each other. Niemeijer slowly increases the lateral tension. After a few minutes a dull blow sounds. The plates have shifted an invisible piece, the tension on the meters immediately decreases. “That’s how an earthquake works,” says Niemeijer.
Niemeijer is university teacher earthquake mechanisms and head of the high pressure and temperature lab of Utrecht University, one floor lower. He points to various devices to “compress, melt and bake in short stones.” Niemeijer: “You have to bridge a time scale: the experiments here take a day to a few weeks, in nature everything takes much longer.”
Since 2014 they are also investigating the induced quakes in Groningen. Gas extraction changes the pressure in the substrate. This sounds the sandstone layer and voltage differences are created along fractures. If the tension becomes too great, an earthquake can take place, as Niemeijer has just shown. The gas extraction in the Groningen field, the largest in Europe, stopped more than a year ago, but the quakes continue.
Work induced earthquakes other than natural?
“They are very similar. The earthquakes in Groningen are very shallow, but three kilometers. The rocks and circumstances are different there. That is also the rankingthe movement on the surface, relatively large for such small earthquakes. And the fractures in Groningen have not been active for millions of years. Before we started the gas production there was no tectonic activity: we have no mountains, no plate boundaries. We simulate that in the lab by creating a break, moving a little and then stopping it again. If you start moving again after a while, the break has become stronger. “
What makes that?
“For example, by dissolving and knocking down material in the break. It was interesting that some materials we mimic under the conditions of Groningen – 100 degrees – had become so strong that when we started moving again, an earthquake took place in the lab. Even though according to previous tests they were not sensitive to earthquakes. Earlier under the conditions of Groningen, it also means that the earthquake models that we used do not take the correct fracture strength. ”
Everything we have learned now helps not to make the same mistake again
Why did you only start in 2014? Gas has been won since 1963.
“Until 2012 there was no one who really rang the bell. In 2012, the Huizinge government was, with a magnitude of 3.6 the biggest ever. As a result, we suddenly could no longer restrict the maximum possible magnitude of the earthquakes. The Huizinge-beverage Quarter achieved the whole Hazard-Model upside down. Then the NAM invited us to do research. “
Did that influence the decision to stop winning?
“No, because it was immediately clear that gas production caused the earthquake. So the only way to prevent the earthquakes from getting worse was to stop.”
What was the approach of the investigation?
“Better understanding for future applications. Everything we have learned now helps not to make the same mistake again. It is really unique how much we have measured in Groningen, sampled and modeled. Use universities around the world that data. And we try to give the prediction model a better basis. Now we are also doing a lot of research into other activities in the substrate: geothermia: geothermia: geothermia: geothermia: geothermia: geothermia2-Storage, hydrogen. Not specifically for Groningen, but everywhere. ”
The gas production has stopped, but there are still earthquakes. How long can they continue?
“That is very difficult to predict, because you do not know what the current tension is on the fractures and whether it will change. Also because the pressure in the field still has to be the same everywhere, that just takes time. It can still take another 10 years or 100 years. Because it is not to model: it is such a large area, with more than 1,300 fractures. I can’t imagine that we are still actively changing. If I say that now and tomorrow there is a larger earthquake, I was wrong. “
It cannot be modeled: it is such a large area, with more than 1,300 fractures
Why does that chance still exist? Because physically it is very illogical.
“Pure statistics. If you look at the distribution of earthquakes, then the chance of a larger earthquake is still present. You are no longer changing the tension, but at the same time we see that there are still many earthquakes. So the substrate is still changing.”
You have also done research in Italy, where natural earthquakes occur.
“Coincidentally, I was just about nine in 2009 when there was an earthquake, the only one I ever felt. I woke up in the middle of the night, the empty clothes hangers in my closet went back and forth. I was in Rome, a hundred kilometers from the epicenter. That was very exciting and impressive. There was so much energy then I would never have been released at the earthquake, I also want to, I also wanted to, I also wanted to, before, for I also. Geophysics, there was a complete chaos.
Did they see it coming?
“No, that remains the difficult thing about earthquakes. There was an elevated activity and that can mean two things: that a larger earthquake arrives, or that the tension of the fractions is going on and there is no large earthquake. But it really depends on the details and where exactly which fractures move. We don’t know enough about the substrate to well predicting that well.”