The extent of damage in Washington, DC, from the 2011 Mw 5.8 Mineral, VA, earthquake was surprising for an epicenter 130 km away; U.S. Geological Survey “Did-You-Feel-It” reports suggest that Atlantic Coastal Plain and other unconsolidated sediments amplified ground motions in the city. We measure this amplification relative to bedrock sites using earthquake signals recorded on a temporary seismometer array. The spectral ratios show strong amplification in the 0.7 to 4 Hz frequency range for sites on sediments. This range overlaps with resonant frequencies of buildings in the city as inferred from their heights, suggesting amplification at frequencies to which many buildings are vulnerable to damage. Our results emphasize that local amplification can raise moderate ground motions to damaging levels in stable continental regions, where low attenuation extends shaking levels over wide areas and unconsolidated deposits on crystalline metamorphic or igneous bedrock can result in strong contrasts in near-surface material properties.
|Title||Amplification of earthquake ground motions in Washington, DC, and implications for hazard assessments in central and eastern North America|
|Authors||Thomas L. Pratt, J. Wright Horton, Jessica Munoz, Susan E. Hough, Martin C. Chapman, C. Guney Olgun|
|Publication Subtype||Journal Article|
|Series Title||Geophysical Research Letters|
|Record Source||USGS Publications Warehouse|
|USGS Organization||Geologic Hazards Science Center|