It's the most well-known US fault, but the San Andreas Fault's southern section hasn't been behind a major earthquake since a 7.9-magnitude temblor in 1857—and that's got Thomas Jordan worried, the Los Angeles Times reports. "The springs on the San Andreas system have been wound very, very tight," Jordan, the director of the Southern California Earthquake Center, told Wednesday's National Earthquake Conference. "And the southern San Andreas fault, in particular, looks like it's locked, loaded, and ready to go." The area (which includes Los Angeles on its periphery) is due for a major quake, Jordan says, adding it's imperative Southern California continue to prepare, following the example of LA in pushing quake retrofits for buildings, as well as protecting telecommunications and water systems. "An earthquake on the San Andreas would really affect all of Southern California," said Jordan's SCEC colleague, Mark Benthien, per CBS Los Angeles.
In tectonics-speak, the San Andreas Fault—which Curbed Los Angeles calls a "ticking ... time bomb"—is where the Pacific Plate and the North American Plate meet, and the Pacific Plate is shifting northwest of the North American one at a rate of 16 feet or so every century, ScienceAlert notes. That's a lot of tension that needs to be released, which would be devastating: A 2008 USGS study found a 7.8-magnitude quake on the San Andreas Fault's southern portion could cause 1,800 fatalities, 50,000 injuries, and $200 billion in damage. Other parts of the fault have also remained dormant even longer, including in San Bernardino County (no major shakeup since 1812) and near the Salton Sea, more or less steady since the late 1600s. "We are fortunate that seismic activity in California has been relatively low over the past century," Jordan said last year. "But we know that tectonic forces are continually tightening the springs … making big quakes inevitable." (Meet the San Andreas' "equally dangerous" partner.)