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The five largest continental transform earthquakes since 2000 all originated on a branch of the main fault—and two researchers predict that the next great earthquake of this type will also get its start on a branch or splay fault.

Last year's magnitude 7.8 Pazarcık earthquake in Türkiye was one of these large and damaging earthquakes, where two continental tectonic plates slide past each other horizontally. That earthquake began on a branch fault, as did the 2001 magnitude 7.8 Kokoxili earthquake in northern Tibet, the 2002 magnitude 7.9 Denali earthquake in Alaska, the 2008 magnitude 7.9 Wenchuan earthquake in China, and the 2016 magnitude 7.8 Kaikōura earthquake in New Zealand.

There are about 25,000 kilometers of continental transform faults across the globe, including some famous ones such as the San Andreas Fault, New Zealand's Alpine Fault and Türkiye's North Anatolia Fault. When their time comes to rupture, will they begin on a branch?

In Seismological Research Letters, Ross Stein of Temblor, Inc. and Peter Bird of the University of California, Los Angeles propose that branch faults act as "on-ramps" to generate rupture on the more mature "superhighway" continental transform faults.

At the moment, Stein and Bird's prediction is a hypothesis that needs more testing, they acknowledge. But magnitude 7.8 or larger earthquakes take place every two to five years on average on these faults, so we shouldn't have too long to wait to see if their prediction holds up.

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