Part of DC's Mall may be sinking faster than normal

Reuters News
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Posted: Mar 15, 2012 11:53 AM
Part of DC's Mall may be sinking faster than normal

WASHINGTON (Reuters) - Part of the National Mall near the Washington Monument may be sinking at a faster rate than expected, possibly as a result of an August earthquake, a spokesman for the National Oceanic and Atmospheric Administration (NOAA) said on Thursday.

Surveyors have found the area around the earthquake-damaged monument has subsided about 0.08 inch (two millimeters) in a year, about twice the expected rate, said NOAA spokesman Ben Sherman.

He called the data "very, very preliminary," with a final finding possible in June.

"The Washington Monument would sink if the ground sinks. It's all relative," he said.

The drop, a bit more than the thickness of a penny, means more planning might have to be done for repairs, Sherman said.

A 5.8 magnitude earthquake on August 23 could explain the early subsidence finding, he said.

Most of the area west of the Washington Monument on the two-mile-long Mall is built on relatively soft landfill dredged from the Potomac River in the 19th century.

The 555-foot-high monument was damaged in the earthquake and is closed to the public. The early findings on subsidence come from a National Geodetic Survey crew carrying out measurements for the company hired to do repairs, Sherman said.

The data would also help the Geodetic Survey, a NOAA unit, to establish a baseline for Mall subsidence. The last measurement was done in 1999.

(Reporting By Ian Simpson; Editing by Daniel Trotta)