Almost half of California's faults — including San Andreas — are overdue for earthquakes

California's earthquakes are far more likely to be "overdue" compared with earthquakes in the rest of the world.

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Many of California's faults, including the southern portion of the San Andreas, are overdue, Mouslopoulou said. She and her colleagues wanted to compare this overdue pattern to the patterns in other regions of the world.

They gathered records from the state and four other quake-prone regions: Japan, Greece, New Zealand, and the Basin and Range province, which covers much of Nevada, Utah, Arizona and northwestern Mexico. These geological records come from trenches that were dug into fault lines so researchers can see when and where the ground broke in the past.

The study showed that while about 45% of California's faults are overdue compared with the mean duration of their seismic cycle, faults in the rest of the world are early — less than 20% were overdue in each of the other regions studied, the researchers reported April 18 in the journal JGR Solid Earth.

That may be an issue, Mouslopoulou said, because California's earthquake data feed into seismic forecast models for faults around the world. This means the models may be skewed by California's current outlier patterns.

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