Regional Geology and Seismic Site Amplification in the Washington, DC, Metropolitan Area

Abstract

The aftermath of the 2011 Mineral, VA earthquake raised concerns on site amplification effects in Washington, DC and the overall Central and Eastern United States (CEUS) region. Current design guidelines for site amplification are set by the National Earthquake Hazard Reduction Program (NEHRP) and are based on research primarily from the Western United States (WUS). However, geology in the WUS and the CEUS differ due to disparate levels of seismic activity. Frequent seismicity in the WUS results in gradually weathered rock, whereas CEUS rock is more intact at shallow depths. This results in impedance contrasts which affect site amplification. This paper presents a study of the site response characteristics of 62 sites in the greater Washington, DC area. Subsurface modeling and equivalent linear site response analyses were performed at each site. The results of this study indicate that current NEHRP design guidelines are inadequate for Washington, DC, specifically for the short-period site amplification factor, F a . Consequently, the city is at risk of greater than anticipated ground surface shaking intensity in the event of an earthquake.