The central section of the fault line has not had a major earthquake in 2,000 years, but that doesn’t mean it can’t produce one
The findings were published in the journal Geology, and found that earlier assumptions about the scale of possible earthquakes produced by the fault line were underestimates.
According to the research, scientists previously believed that a central section of the fault produced less severe earthquakes than other sections of the fault. However, the study’s authors concluded that large magnitude earthquakes are possible in the area and have happened in the past.
The San Andreas Fault is an 800-mile stretch through California where the Pacific and North American tectonic plates meet. The fault runs from north of San Francisco to San Diego.
Researchers previously believed that the largest earthquakes were formed at the ends of the fault, where immense pressure can build over time, releasing in major quakes.
California regularly experiences earthquakes, with southern California logging 10,000 each year. Most of these are minor quakes that are imperceptible to residents of the state. Only about 15 to 20 in the area are greater than a 4.0 each year.
However, major earthquakes have happened, like, the 7.9 magnitude quake that hit San Francisco in 1906, which killed more than 3,000 people. Another 57 people died in 1994 after a 6.7 magnitude quake occurred near Los Angeles.
According to the researchers, the central section of the fault line, which runs through the central coastal region of California, has not had a major earthquake in 2,000 years. However, they found that larger earthquakes had happened in the distant past.
The scientists’ analysis determined that rocks in the central fault section had been moved more than five feet, largely due to earthquakes in that region. That equates to earthquakes of a 6.9 magnitude in the past.
“Ultimately, our work points to the potential for higher magnitude earthquakes in central California and highlights the importance of including the central [San Andreas Fault] and other creeping faults in seismic hazard analysis,” the study concluded.
Dr Genevieve Coffey, the lead author on the study and an earthquake geologist at Columbia University’s Lamont-Doherty Earth Observatory, told Columbia Climate School news that the findings should alert other researchers to the potential for large earthquaks originating in the region.
“We should be aware that there is this potential, that it is not always just continuous creep,” she said.