Washington ? Everyone has known New Orleans is a sinking city. Now new research suggests parts of the city are sinking even faster than many scientists imagined – more than an inch a year.

That may explain some of the levee failures during Hurricane Katrina and it raises more worries about the future.

The research, reported in the journal Nature, is based on new satellite radar data for the three years before Katrina struck in 2005. The data show that some areas are sinking four or five times faster than the rest of the city. And that, experts say, can be deadly.

“My concern is the very low-lying areas,” said lead author Tim Dixon, a University of Miami geophysicist. “I think those areas are death traps. I don’t think those areas should be rebuilt.”

The blame for this phenomenon, called subsidence, includes overdevelopment, drainage and natural seismic shifts.

As the ground in specific areas sinks, protection from levees also falls, scientists and engineers said. For example, the Mississippi River Gulf Outlet, built more than three decades ago, has sunk by more than 3 feet since its construction, Dixon said, explaining why water poured over the levee and part of it failed.

“The people in St. Bernard got wiped out because the levee was too low,” said co-author Roy Dokka, director of the Louisiana Spatial Center at Louisiana State University. “It’s as simple as that.”