“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.
“These research findings have important implications in terms of seismic hazard and risk assessment in coastal Southern California and are relevant to municipal, industrial and military infrastructure in the region,” said Robert J. Leeper, a former U.S. Geological Survey geologist and graduate student at Cal State Fullerton, who was the lead author of the paper.
“Imagine a large earthquake — and it can happen again — causing the Seal Beach wetlands to sink abruptly by up to three feet,” said Matthew E. Kirby, a Cal State Fullerton professor of geological sciences and co-author of the study.
“This would be significant, especially since the area already is at sea level,” Kirby added.
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.
The wetlands likely were a result of movement along the Newport- Inglewood/Rose Canyon fault system, Leeper said. The fault line runs from Beverly Hills to San Diego, and if it all ruptured at once it could generate a 7.5-magnitude shaker.
“Future earthquakes that result in subsidence of the saltmarsh may present serious hazards to the U.S. Naval Weapons Station Seal Beach, Seal Beach National Wildlife Refuge, Huntington Harbor, and other southern California coastal communities,” the experts write in the study.
The last earthquake to spur an abrupt drop in the level of the wetlands happened about 500 years ago, Leeper said.
—City News Service
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