Earthquakes devastated both Italy and Myanmar early Wednesday. Though the quakes were similarly sized—magnitude 6.2 in Italy and magnitude 6.8 in Myanmar—the seismic events, occurring more than 5,000 miles (8,047 kilometers) apart, were not related.
We asked two experts to explain whether it's ever possible for one earthquake to trigger another. John Bellini is a geophysicist at the U.S. Geological Survey National Earthquake Information Center and Michael Steckler is a geophysicist at the Lamont-Doherty Earth Observatory at Columbia University.
Are the earthquakes in Italy and Myanmar at all related?
John Bellini: No, the two earthquakes are not related. They are located along different faults in different parts of the world. They just happened to occur on the same day. Neither of these is really that large either. Around the world, we have something like 150 earthquakes a year— around two or three a week—in the 6 to 6.9 range.
A large earthquake, something like an 8 or a 9, or even a large 7, can trigger small things nearby, but not on the other side of the world.
Michael Steckler: I don’t think they are related; they are too far apart. For earthquakes this size, the fault length that broke was roughly 30 to 60 miles long (50 to 100 kilometers). You would expect stress from an earthquake to affect another quake within several of those lengths (up to 250 miles). For something this size, it may be even less.
Are these regions typically susceptible to earthquakes?
JB: Both Italy and Myanmar are tectonically active regions, meaning they have a lot of earthquakes. Italy has many smaller earthquakes and can have some in the magnitude 6 range from time to time.
MS: Italy has a catalog of earthquakes going back hundreds of years. In Myanmar, there was another quake about this size earlier this year. There is certainly seismicity in that slab.
JB: The area in Myanmar is similarly active to Italy in the overall amount of earthquakes, but the largest ones in Myanmar can be a quite a bit larger. Italy’s usually top out around 7 magnitudes, but over in Myanmar and Nepal you can have earthquakes in the magnitude 8 range. That’s not to say that Italy will never have an 8 magnitude earthquake, but they are more common in Myanmar.
Italy seems to be experiencing more aftershocks than Myanmar. Why?
JB: They’re just not being recorded in Myanmar. Italy is a highly instrumented country as far as seismicity goes, whereas Myanmar is not. Any earthquakes that appear on our website are probably coming from data that we received from Italy.
The number and size of aftershocks are partially dependent on the size of the original earthquake. It takes some time for the Earth to settle down after the initial shock; aftershocks are really "adjustment" shocks.
These regions will likely experience aftershocks for weeks. For a magnitude 6.2 earthquake, like that in Italy, we would expect multiple aftershocks in the 5 range. Especially in Italy, people need to be aware that shocks of even magnitude 5 can cause additional damage.
Why does the destruction seem to be worse in Italy when the earthquake was larger in Myanmar?
MS: The subduction zone in Myanmar is relatively deep—the epicenter of this quake was 52 miles (84 kilometers) below the surface. When an earthquake is that deep, nobody is closer than 52 miles to the epicenter. It may affect a broader zone but it is less damaging than a shallow quake.
Italy’s earthquake was much shallower, and it was more destructive because of the proximity to the surface. In Italy, they are often building on flat mesas that may shake more, and many buildings are older structures made from stone. These don’t do well in earthquakes.
These interviews have been edited.
Follow Aaron Sidder on Twitter.