Washington, US: The National Geodetic Survey discovered that land near the Washington Monument may have sunk by two millimetres, possibly as a result of the last August’s 5.8 magnitude earthquake.
Speaking to the Washington Post, David Doyle, the National Geodetic Survey’s chief geodetic surveyor, said, “We know that most of this area down here — basically everything from the Washington Monument westward — is constructed on fill. And we know that there is some form of settling, subsidence. The exact rates are small, but over time they can add up and be significant.”
The National Geodetic Survey is a federal agency that compiles precise data on latitude, longitude and elevation above sea level to establish official place locations. The focus is elevation, Doyle added. Using a process called “digital bar code levelling,” he and a surveying crew have been walking the Mall (near the monument) with high-tech optical equipment, measuring current elevations to compare with past measurements. The measuring started in early March and will continue through the end of the month.
Doyle said the early data seem to suggest that there has been two millimetres of sinking where they were expecting subsidence of less than one millimetre.
“That’s way more than we can live with,” he said. “Almost one millimetre could be accounted for just in normal settlement. Something beyond that might be a result of the earthquake.
The finding comes soon after the completion of a USD 12 million repair of the Jefferson Memorial’s seawall, which had sunk much more dramatically, almost a foot in places, in recent years.
Source: The Washington Post