The Big One may be overdue to hit California but scientists near Los Angeles have found a new risk for the area during a major earthquake: abrupt sinking of land, potentially below sea level.
The last known major quake on the San Andreas fault occurred in 1857, but three quakes over the last 2000 years on nearby faults made ground just outside Los Angeles city limits sink as much as three feet, according to a study published Monday in the journal Scientific Reports.
Seismologists estimate the 1287km-long San Andreas, which runs most of the length of the state, should see a large quake roughly every 150 years.
Scientists from California State University Fullerton and the United States Geological Survey found evidence the older quakes caused part of the coastline south of Long Beach to drop by up to a metre.
Today that could result in the area ending up at or below sea level, said Cal State Fullerton professor Matt Kirby, who worked with the paper's lead author, graduate student Robert Leeper.
"It's something that would happen relatively instantaneously," Kirby said.
"Probably today if it happened, you would see seawater rushing in."
The smallest of the historic earthquakes was likely more intense than the strongest on record in the area, the magnitude 6.3 Long Beach earthquake of 1933, which killed 120 people and caused the inflation-adjusted equivalent of nearly a billion dollars in damage.
Seismologist John Vidale, head of the University of Washington-based Pacific Northwest Seismic Network, said after reviewing the study he was sceptical such powerful quakes could occur very frequently in the area.
Kirby noted that the team could only collect soil core samples within the relatively undisturbed refuge, and that taking deeper samples would shed light on the seismic record even further back, potentially giving scientists more examples of similar quakes to work from.
