Thursday, March 29, 2012
Surveying on the National Mall
The 2011 earthquake near Washington, D.C., shook the nation's capital with enough force to damage the Washington Monument. But not all effects of the earthquake are visible to the naked eye. Experts from the National Geodetic Survey (NGS) are nearing completion of a leveling survey that will help determine whether the ground underneath the Monument shifted because of the quake. This is the first phase of a planned longer-term effort to assist the National Park Service (NPS) by regularly surveying the grounds of the National Mall.
The rare 5.8-magnitude earthquake on August 23, 2011, shook the nation's capital with enough force to crack stones and loosen mortar in the Washington Monument. While preliminary analysis indicate that the earthquake did not cause significant vertical motion in the Washington Monument, even slight changes could affect plans for repairing the stone obelisk.
The survey is initially focusing on whether any abnormal displacement of the Monument resulted from the earthquake. Later this year, NGS surveyors will also take GPS measurements from the top of the Washington Monument to determine if the stone obelisk tilted due to the quake. Engineering firms under contract to NPS will use the survey results in the planned $15 million restoration efforts to repair the stone structure.
Beyond determining the effects of the earthquake, NGS surveyors are concurrently collecting miles of leveling data in the downtown Washington, D.C. area that they expect to update every three to five years. The National Mall is built largely on landfill and is slowly settling over time, causing ongoing maintenance concerns with many of the heavy monuments in the area. This long-term effort will provide the Park Service with better information to help in the preservation of historical structures, while providing a low-cost field training opportunity for NGS personnel.
NGS and its predecessor agency have conducted periodic surveys of National Park Service sites around Washington since 1884.
You can learn more about the study, view photos, and listen to an audio podcast on NOAA's National Ocean Service website.
For more information, contact Dave Doyle.
