The magnitude of an earthquake depends on how far a rupture travels along a fault line before it stops. For the first time, we have now directly observed how a large earthquake comes to a halt.

By analysing seismic recordings taken within a few kilometres of faults, we have identified a ground motion signal we call a “stopping phase”. It records the moment the earthquake stops.

This discovery, published in Science today, provides direct seismic evidence that large ruptures stop suddenly, rather than slowing down gradually.

It also helps identify where shaking may be strongest along strike-slip faults, which could help with disaster planning and preparation.

Earthquakes grow as the rupture spreads along a fault. The further it goes, the larger the earthquake magnitude becomes. The vast majority of earthquakes stop before they grow large enough to be felt.

For example, the earthquake monitoring network GeoNet has recorded more than 20,000 earthquakes in Aotearoa New Zealand over the past year, but all stopped soon after they began.

A very small percentage of earthquakes keep on going, and can travel for many hundreds of kilometres before coming to a halt, reaching up to magnitude 9 and often causing widespread damage.

Although rupture stopping is clearly........

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