"A rare 5.8-magnitude earthquake struck the Piedmont region of Virginia on August 23, 2011, shaking the Nation's capital with sufficient force to crack stones and loosen mortar in the Washington Monument (WM). Scaffolding built around the structure to facilitate repairs made to the building in 2013 and 2014 provided a rare opportunity for NOAA's National Geodetic Survey (NGS) to perform a geodetic survey incorporating direct occupation of the WM peak with multiple instruments. Although NGS-formerly the U.S. Coast and Geodetic Survey (USC&GS)-surveyed points at the base of the WM many times in the building's 120-plus year history, only twice before (in 1934 and 1999) had full scaffolding allowed surveyors access to the peak of the structure. The 1934 and 1999 surveys were of insufficient accuracy to detect whether any subtle changes had taken place in the peak's three-dimensional location in space. The new scaffolding provided NGS the opportunity to once again collaborate with the National Park Service (NPS) to survey the peak of the WM, this time with greater accuracy than previously achieved. NGS' primary goal for the new endeavor was to position the peak within the National Spatial Reference System (NSRS), and as a secondary goal, to provide a building height measured to an international standard"--Executive summary.

National Ocean Service (NOS)

Washington (D.C.)