LOS ANGELES, March 26 (Xinhua) -- A new research showed evidence of abrupt sinking of one of Southern California's top seismic danger zones caused by ancient earthquakes that shook the area at least three times in the past 2,000 years.
It could happen again, the researchers warned.
The Newport-Inglewood fault, which is located along the western margin of the Los Angeles Basin, has long been believed to be one of major California seismic faults because it runs under some of the region's most densely populated areas.
But the California State University, Fullerton (CSUF) faculty-student study shows that the fault is more active than previously thought.
The research, published this week in Scientific Reports, an open-access, peer-reviewed Nature research journal, has uncovered evidence of abrupt sinking of the wetlands of Seal Beach near the Orange County coast, California, caused by ancient earthquakes on the Newport-Inglewood fault at least three times in the past 2,000 years.
"Imagine a large earthquake -- and it can happen again -- causing the Seal Beach wetlands to sink abruptly by up to 3 feet. This would be significant, especially since the area already is at sea level," Matthew E. Kirby, CSUF professor of geological sciences, said in a statement.
Scientists took 55 samples of sediment underneath the Seal Beach National Wildlife Refuge in southern Los Angeles, by submerging 20-foot-long, sharp-tipped pipes that collected samples of the sediment, mapping buried layers for signs of past seismic activity.
Samples analyses, combined with the study of microscopic fossils to identify the past environment, found evidence of sinking in the area from past massive earthquakes. The study identifies three previously undocumented earthquakes in the area over the past 2,000 years. The last big quake to cause the land to abruptly drop occurred approximately 500 years ago, researchers said.
The 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, according to the study.