Early Monday morning, an magnitude 7.8 . earthquake tearing up Turkey and Syria, nine hours later a 7.5 aftershocks. Number of dead people standing at more than 3,800and rescuers have only just begun scouring the collapsed buildings.
Aftershocks will continue to shake the region as local faults adapt to such large initial tremors, and scientists say that process could continue not just days but months or even even many years. There is even a possibility—though small—of aftershocks bigger than the original earthquake.
“The risk of aftershocks is essentially greatest immediately after the main quake, but there will be noticeable aftershocks to this quake over many years,” said David Oglesby, geophysicist at UC Riverside. Later. “Right now, I can predict to you that there will be many aftershocks stronger than 5, maybe 6 or more, in this area. It’s an easy decision to make, because historically speaking, it’s almost guaranteed.”
That would make the humanitarian crisis in Turkey and Syria worse. “We cannot tell people: OK, fine, you’re done. It was horrible, and now it’s over. Because that’s not how the earth works,” says earthquake geologist Wendy Bohon. “It’s bad to know that these people will have to continue to feel the tremors of the earthquake for a long time, after they’ve been so traumatized and through such a devastating experience.”
Earthquakes are products of plate tectonics: Plates are large blocks of rock that move independently in the earth’s crust, but are in contact with each other along faults. “Ultimately, stress and tension will overcome the friction that is holding the rocks together, and those rocks will break apart in an earthquake,” says Bohon. “When the rocks break, they release energy in the form of waves, and those waves are what we feel like shaking.”
Monday morning’s quake struck along about 125 miles of the East Anatolian Fault, a well-known fault line in southern Turkey. Specifically, this is a transverse slip earthquake, meaning that the stresses formed between two rock masses that move horizontally in opposite directions until the fault ruptures. It’s also very shallow underground, which means it produces more intense shaking than on the surface. (The San Andreas Fault in California is also a transverse slip fault—this fault destroyed much of San Francisco in 1906.)
In general, the larger the primary tremor, the larger the aftershock, which tends to decrease in frequency and severity over time. As you can see in this map, aftershocks of varying magnitudes flooded along the fault line of the original earthquake as well as at another fault line connected to the north, where a magnitude 7 aftershock appears to have occurred. 5 degrees richter. “This is a really complicated fault system, because the crust is really crushed there,” said Alice Gabriel, a seismologist at the Scripps Institution of Oceanography.
That complexity means that what happens in an error doesn’t stop there. It’s possible that the pressure that led to the 7.5 magnitude quake had been building for some time, and the shock from the quake released it. Austin Elliott, an earthquake geologist at the US Geological Survey, said: “Its clocks went up a little bit, so it has the big quake that it’s going to eventually, there’s a big quake that it’s going to have to eventually, have maybe a little earlier. Such aftershocks “are simply other earthquakes—nothing makes them different. It’s just that one earthquake so large changes the stresses in the earth’s crust that it speeds up all other local earthquakes.”
