There have been no major ground rupturing earthquakes along California’s three highest slip rate faults in the past 100 years. A new study published in Seismological Research Letters concludes that this current “hiatus” has no precedent in the past 1000 years.
U.S. Geological Survey researchers Glenn Biasi and Kate Scharer analyzed long paleoseismic records from the San Andreas, San Jacinto and Hayward Faults for the past 1000 years, to determine how likely it might be to have a 100-year gap in earthquakes across the three faults. They found that the gap was very unlikely—along the lines of a 0.3% chance of occurring, given the seismic record of the past 1000 years.
The results emphasize that the hiatus is exceptional, and that the gap isn’t some sort of statistical fluke created by incomplete paleoseismic records, said Biasi.
The analysis also indicates that the next 100 years of California earthquakes along these faults could be a busy one, he noted. “If our work is correct, the next century isn’t going to be like the last one, but could be more like the century that ended in 1918.”
Between 1800 and 1918, there were eight large ground-rupturing earthquakes along the faults, including the well-known 1906 earthquake in San Francisco and the similar-sized 1857 rupture of the San Andreas in southern California, but nothing so large since.
“We know these big faults have to carry most of the [tectonic] motion in California, and sooner or later they have to slip,” said Biasi. “The only questions are how they’re going to let go and when.”