The two earthquakes in Spain today (May 11) that killed several people and caused significant damage struck an area with a tame seismic history. Their shallow point of origin contributed to the deaths and destruction.
The quakes ripped masonry and bricks from buildings, according to the Associated Press.
The first quake, a magnitude 4.5, struck at 5:05 p.m. local time, and was followed by a stronger, 5.3 magnitude earthquake almost two hours later, at 6:47 p.m. [7 Ways the Earth Changes in the Blink of an Eye]
The quakes, which occurred along a yet-unidentified fault, were shallow, rupturing just over a half-mile (1 kilometer) below ground, said John Bellini, a geophysicist with U.S. Geological Survey.
"Earthquakes close to the surface cause the most of damage no matter what type of fault it is," Bellini told OurAmazingPlanet.
Footage of the quake broadcast on a Spanish news channel shows a church tower falling to rubble and bricks crashing onto cars on the street below.
The earthquakes appear to have wrought outsize destruction for their relatively low magnitude, a fact that could be due to a prevalence of older buildings in the region.
Bellini said an earthquake of a magnitude 6.5 in Tokyo, a city with strict earthquake codes, built to withstand powerful shaking, would likely cause very little damage. But in a place like this area of Spain, where earthquakes are less anticipated, buildings are less likely to be earthquake-resistant.
"Really the construction of the buildings is what contributes to the potential for there to be damage," Bellini said.
The region of coastal Spain where the earthquakes struck does have a history of seismic activity, albeit a fairly tame one.
Since 1976, the USGS has recorded more than half a dozen earthquakes in the area with a magnitude of 5 or greater.
"It's not a very active region, but they do get earthquakes form time to time, so it's not a surprising event," Bellini said. "They just don't happen as frequently as they do in other regions."
- The Biggest Earthquakes in History
- Image Gallery: This Millennium's Destructive Earthquakes
- Are We in an Age of Great Earthquakes?