Does it seem as if there have been more earthquakes in recent weeks? Some scientists thought so. Some of the best minds in earthquake science have been counting quakes and analyzing seismic waves to see if the largest in a string of recent quakes — the magnitude-8.2 tremor in Chile on April 1 — might have triggered others far, far away. Ross Stein, a senior U.S. Geological Survey geophysicist who studies how quakes interact, got so excited that on April 12 he fired off an email to colleagues that started with this: “Guys, seems like a lot of big quakes have been popping off around the globe over the past week.” Experts for years have known that the seismic waves from one quake can trigger a quake somewhere else — a process known as “dynamic triggering.” Stein himself co-authored a study tying a magnitude-8.7 Indian Ocean quake in 2012 to a spike in quakes globally in the days after. That increase lasted about a week, and a few days after the spike, the rate for larger quakes fell to below average. “It’s as if the Indian Ocean quake had shaken the tree, causing the apples ready to fall out to do so,” said Thorne Lay, a seismology professor at the University of California at Santa Cruz.. Lay’s own research has found that over the last decade the number of major quakes, those measuring 8.0 or bigger, is nearly triple the rate for the 1900s, but whether that’s just a random cluster or a sign of dynamic triggering is unclear.
In any case, the latter possibility is what got experts like Stein and Lay wondering if the Chilean quake had triggered others. A 7.2 on Mexico’s Pacific Coast on April 18 and a 7.5 off Papua New Guinea two days later were the latest to get attention Doing a quick review of quakes magnitude 6 or larger and which struck within the upper 43 miles (70 kilometers) of Earth’s crust, Lay found an uptick when comparing April 1-18 to the first three months of 2014. But the increase wasn’t significant, so the question remained: Did dynamic triggering play a role, or was that just random chance? “That’s a harder problem to answer,” Lay said. Seismic wave data from the Chilean quake was studied by UC Santa Cruz grad students to see if it might have triggered one in Nicaragua nine days later. “We did not see anything obvious,” Professor Emily Brodsky said of her team’s work. Stein, like Lay, also counted quakes but looked instead at moderate and large quakes (4.5 magnitude or greater) in the 10 days before and after the April 1 quake that struck Iquique, Chile. In his email to peers, Stein concluded: “I do not see a global increase in activity post-Iquique, at least for moderate and larger quakes — the ones that matter for hazards.” “[It] seemed like a lot of big quakes” after Iquique, he later told NBC News, “but it’s largely an illusion.” That letdown is part of the reality of earthquake science, which is still in its infancy. “We have false hunches all the time,” Stein said. “We don’t want to miss something.” Making more sense of quakes, especially dynamic triggering, could be helped by a wider network of monitoring equipment. But that’s no easy task. More