Earthquakes on California are more likely to be “late” than on other similar faults, according to a new study. (Photo by Kevin Schaefer/Getty Images)
California is a seismically active region because faults in the state are more likely to be “delayed” than faults in other parts of the world, new research suggests.
Lead author of the study, Vasiliki Mouslopoulou, a research geologist at the National Observatory of Athens in Greece, notes that the findings could help geologists more accurately estimate when faults are likely to fail and cause earthquakes, even in vulnerable California.
“The important thing to understand is that this is going to benefit everyone, including California,” Mouslopoulou told Live Science.
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Mouslopoulou and her colleagues became interested in studying the recurrence intervals of earthquakes on faults with a long geological history of rupture. Earthquake scientists use these records to estimate the likelihood of future earthquakes on a fault by comparing the time since the last known major earthquake with the average time between two major earthquakes in the fault’s history. If the fault rocks show signs of rupture every 150 years, and it’s been 200 years since the last earthquake, the earthquake is considered “late.”
Many faults in California, including the southern San Andreas, are considered overdue, Mouslopoulou said. She and her colleagues sought to compare this overdue pattern with patterns in other parts of the world.
They collected data from California and four other earthquake-prone regions: Japan, Greece, New Zealand, and the Basin and Range Province, which covers much of Nevada, Utah, Arizona, and northwestern Mexico. The geologic data came from trenches dug along fault lines so the researchers could observe when and where the land had ruptured in the past.
The study found that about 45% of California's faults were overdue compared to the average length of their seismic cycles, while in other regions, less than 20% of faults were overdue, the researchers reported April 18 in the journal JGR Solid Earth.
This could be a problem, according to Mouslopoulou, because earthquake data from California influences seismic prediction models for faults around the world, meaning current models could be biased by existing conditions in California.
She and her colleagues believe that to better understand faults on a global scale, researchers can use the time between historical ruptures and penultimate events, rather than the time since the last earthquake. This methodology better predicts the patterns of earthquakes that actually occur on faults outside California, Mouslopoulou said.
One of the reasons California is an anomaly in terms of earthquakes is that the San Andreas Fault and the faults surrounding it are fast moving, meaning they are actively slipping and regularly producing earthquakes. This relatively frequent repetition
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