Why Are Some Earthquakes So Much Worse Than Others?

Earthquakes are more intense the faster the planet’s crust slams together, which explains why the shaking causes so much damage in some of the most populated areas around mountain chains.

Scientists were trying to understand why some tremors are more intense than others. They used models of tectonic plates and their movement to make their findings and found that, according to their paper in the journal Earth and Planetary Science Letters, the speed at which those plates were crashing into one another was directly linked to how frequent and how powerful the resulting earthquakes were.

One reason for this connection is that when two plates come together quickly, the area over which an earthquake occurs is larger. Other factors play a role as well, such as the geological history of the place, the stress on the plates, and temperature. According to the study, fast-moving plates lead to cooler temperatures and make the crust more “brittle,” which allows it to release more of the energy it has built up.

“The impact of large earthquakes in mountain belts is devastating,” lead study author Luca Dal Zilio, from Swiss university ETH Zürich, said in a statement from journal publisher Elsevier. “Our scientific contribution can help the society to develop a more complete view of earthquake hazard in one of the most densely populated seismic zones of the world and ultimately take action accordingly.”

The models the team used in their investigation mimicked the conditions at four different mountain ranges in Europe and Asia: the Himalayas, which are home to Mount Everest; the Alps, the biggest mountain chain in Europe; the Zagros, which are mostly in Iran; and the Apennines in Italy. In those mountain ranges, smaller tectonic plates — separate from the seven major plates on Earth that people tend to be familiar with — rub together to create the quakes that are hazardous to the dense human settlements around them. Where the plate collisions are slower, there is less danger associated with the seismic activity.

Mountains themselves can rise up from the ground due to movement in the Earth’s crust and mantle with tectonic plates colliding.