Part of the San Andreas fault may be gearing up for an earthquake

A section of the San Andreas fault where earthquakes occur regularly may give off a distinct signal before it trembles to life, new research finds. The signal hints at the opening and closing of cracks beneath the subsurface.

This section of faultline, known as Parkfield in Central California, shakes regularly about every 22 years. It last ruptured in 2004, so another earthquake may be imminent. However, the signal is not currently occurring at the fault segment, and the section isn't behaving exactly like it did the last time it ruptured, according to a study published March 22 in the journal Frontiers in Earth Science.

The differences might mean the next quake won't happen right away, or they might mean that the epicenter of the quake will be different from 2004's epicenter, which was just southeast of the tiny town of Parkfield. There will be no way to know until the next quake actually happens, said study lead author Luca Malagnini, the director of research at the National Institute of Geophysics and Volcanology in Italy.

"We are waiting," Malagnini told Live Science.

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The San Andreas fault marks the boundary between the Pacific and North American tectonic plates. South of Parkfield, the fault is locked, meaning the two plates do not move against one another. North of Parkfield, the San Andreas fault moves freely, with the plates creeping against one another at a constant rate of 1.4 inches (3.6 centimeters) a year. Parkfield is a transitional zone between these two regimes. When this region of the fault rumbles to life, it gives off a quake of around magnitude 6. Because of the remote location, these quakes rarely threaten human life or property, though quakes on one fault can affect stresses on other nearby faults, Malagnini said.

But researchers watch Parkfield closely in hopes of finding activity that will help them predict when the next quake will occur. Being able to detect reliable precursors to earthquakes — strain on rocks for example, or changes in permeability under the surface — would help scientists warn people about imminent temblors, potentially saving lives. Parkfield, with its recurring quakes, might be a good place to look for these clues to extrapolate to more dangerous fault segments. But so far, that goal has been elusive.