HUNTINGTON BEACH (CBSLA.com) – A new study published Monday in the journal Nature shows there were three major earthquakes over the last 2,000 years in the Seal Beach wetlands, causing the area to abruptly drop a few feet, a phenomenon likely to happen again and cause major devastation to the coast.
Local geologists have new evidence along the Newport-Inglewood fault that during large prehistoric earthquakes with a magnitude of over 7.0, the wetlands dropped between one-and-a-half and three feet in a matter of seconds. The question scientists have now is which coastal communities could be at risk of sinking.
“If you were standing on the Seal Beach wetlands during one of these large earthquakes, you would instantaneously drop three feet,” Cal State Fullerton Geology Professor Matthew Kirby told CBS2 Tuesday.
Kirby led the research study, which used soil samples gathered in a nature preserve in Orange County.
“During a large earthquake along this fault we’d see instantaneous sinking of the wetlands, we’d see water coming in from the ocean filling that spot,” Kirby said. “You’d probably have differential liquefaction as a result of the type of sediments. It would be pretty bad.”
The Newport-Inglewood Fault runs from Beverly Hills to Newport.
“Comparing the Seal Beach saltmarsh data set to these criteria suggests that the abrupt burial events are consistent with the hypothesis that earthquakes along the Newport-Inglewood fault system resulted in coseismic subsidence of the relic wetlands surface three times in the past 2000 years, occurring approximately every 700 years,” the authors write in Nature.
The 500-acre wetlands is within the Naval Weapons Station Seal Beach. The study indicates more earthquakes could have happened in the recent path in the area that had been earlier assumed.
Along the Pacific Coast Highway is Huntington Harbour, heavily developed and with homes built on the fault line.
“Well certainly if I was living in the Huntington Harbor area today, knowing it’s built on what were once wetlands, I would probably be a little more concerned than I was a day ago.”
The last earthquake to spur an abrupt drop in the level of the wetlands happened about 500 years ago, according to Robert J. Leeper, a former U.S. Geological Survey geologist and graduate student at Cal State Fullerton who was the lead author on the paper.
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