Italy’s earthquake was a lot weaker than a recent one in Myanmar, but it did far more damage because it happened at a shallower depth.
A quake’s destructive force depends not only on its strength, but also on location, distance from the epicentre, and depth. Quakes can strike near the surface or deep within the Earth. Most quakes occur at shallow depths, according to the USGS.
Italy’s quake was very shallow, originating between 4km and 10km underground, according to Italy’s geological service and the USGS. The magnitude measurements also varied slightly – between magnitude 6 and 6.2.
By contrast, the 6.8 quake in Myanmar was deeper – at 84km, which is an intermediate depth.
Shallow quakes generally tend to be more damaging than deeper quakes. Seismic waves from deep quakes have to travel farther to the surface, losing energy along the way.
In quakes that hit close to the surface, shaking is more intense, like setting off “a bomb directly under a city”, said a USGS seismologist.
The Italy quake destroyed three towns, home to ancient structures built before there were building codes. Many buildings were made of brick or stone, which can fall apart during shaking.
They’re very quaint, but they don’t withstand earthquakes very well,” Hough said.
Deep quakes may be less damaging, but they’re usually more widely felt.
Most of the destruction in the Myanmar quake was centred in the tourist town of Bagan where nearly 100 brick pagodas dating back centuries were damaged.
At least four people were killed in the Myanmar quake, which also shattered ancient Buddhist pagodas.