August 25, 2016

Are The Italy And Myanmar Earthquakes Connected? A Similar Magnitude Had Different Effects. Two Experts Are Asked To Explain Whether The Dual Disasters Were Isolated Events.

National Geographic
written by Aaron Sidder
Wednesday August 24, 2016

We asked two experts to explain whether the dual disasters were isolated events.

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.

written by Madhuri Sathish
Wednesday August 24, 2016

Just hours after a magnitude 6.2 earthquake struck central Italy, a magnitude 6.8 earthquake struck Myanmar, thousands of miles away. According to National Geographic, both earthquakes happened near two of the world's major fault lines, in regions with significant geological volatility. But the Italy and Myanmar earthquakes were not connected to one another, even though they struck on the same day. The earthquakes' different impacts on the regions they affected can be explained by the depth below the earth's surface at which each earthquake took place.

The death toll of the Italy earthquake has risen to at least 159, according to CNN, and multiple towns were devastated as buildings collapsed. The Myanmar earthquake left at least three people dead, The New York Times reported, and over 170 temples were damaged. The earthquakes seemed similar in magnitude, so why were their impacts so different? Susan Hough, a seismologist with the U.S. Geological Survey, explained to USA Today that while Italy's quake took place roughly six miles below the earth's surface, the earthquake in Myanmar took place at a much greater depth, approximately 50 miles underground.

Deeper quakes tend to cause less damage — which explains the disparities in death tolls — but they also tend to be more widely felt. That's why the earthquake in Myanmar, which took place at an intermediate depth, was felt in Thailand, Bangladesh, and India. The reason deeper earthquakes cause less damage is that seismic waves have to travel further to reach the surface of the earth, and they lose energy along the way. In Italy's case, however, the earthquake took place at a much shallower depth. Consequently, the shaking was more intense in Italy than in Myanmar because it was like setting off "a bomb directly under a city," Hough told the Associated Press.

Earthquakes in different regions can sometimes impact each other by sending out shockwaves that impact other fault lines, Hough told USA Today, but she added that the quake in Italy was not nearly big enough to have caused the Myanmar earthquake. However, the two quakes definitely do indicate that both regions are geologically volatile. As National Geographic pointed out, Italy is near a fault line along the Apennine Mountains, in an area between Eurasian and African tectonic plates that is "tectonically and geologically complex." Myanmar, meanwhile, is located east of the Sunda Trench, where earthquakes are common.

As a result of where they are located, both Italy and Myanmar have experienced devastating earthquakes in the past. But even though they have this in common, the earthquakes that both countries experienced on Wednesday were still extremely different, and when discussing and analyzing the impact quakes have, it is important to keep factors like depth and location in mind.

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