Thursday, August 25, 2016

Why the Italy Quake Was So Severe

[NY Times] The combination of a shallow fault and old, unreinforced masonry buildings led to widespread devastation in the earthquake that struck central Italy early Wednesday.
The magnitude-6.2 quake killed at least 241 people and left hundreds more injured. Many people were trapped in the rubble of collapsed buildings.
Like other villages and towns in the mountainous area, Amatrice, where the mayor lamented that “half the town no longer exists,” has stone churches and other buildings that were constructed centuries ago, when little if anything was known about earthquakes. Unless they have been reinforced in recent years, such structures are easily damaged or destroyed by shaking.
“Even 100 years ago, they didn’t know how to build structures to withstand earthquakes,” said David A. Rothery, professor of planetary geosciences at the Open University in Milton Keynes, England.
The earthquake was less powerful than many recent deadly quakes. The magnitude-7.8 earthquake that struck Nepal in April 2015, for instance, killing 8,000 people, released roughly 250 times more energy.
But the Italian quake was very shallow: According to the United States Geological Survey, it occurred about six miles below the surface. “Shallow earthquakes cause more destruction than deep earthquakes because the shallowness of the source makes the ground-shaking at the surface worse,” Professor Rothery said.
Video from Amatrice and other towns near the quake center showed heaps of masonry rubble from buildings that had been shaken apart.
Earthquakes are set off by the movement of the earth’s crust, which is divided into large sections called tectonic plates. The Apennine Mountains, where the quake occurred on Wednesday, are in an area where one plate, the African, is moving under another, the Eurasian. Read More