The speed at which plates of Earth’s crust smash into each other determines how big earthquakes can get in the collision zone.
When tectonic plates converge, they can thrust up mountain ranges that are prone to deadly quakes. One such range is the Zagros, where a quake on 12 November killed hundreds of people in Iran and Iraq.
Luca Dal Zilio at ETH Zurich in Switzerland and his colleagues developed models to simulate quakes in these regions, and modelled collision rates ranging from 1 to 5 centimetres per year. In mountainous zones, the main factor driving both the frequency and the maximum magnitude of quakes was how fast the plates were converging. When plates smash into each other at higher speeds, more of the crust at the collision sites becomes brittle, and that makes the region more prone to large quakes.
The work helps to explain why Europe’s Alps, where plates converge slowly, are less seismically active than the faster-moving Himalayas.