SEISMIC HAZARD MAPPING OF THE NATIONAL CAPITAL REGION USING RANDOM FIELD MODELS

The 2011 Mineral, Virginia earthquake had a Magnitude 5.8 and resulted in significant structural damage in Washington DC, and surrounding areas, at distances in excess of 120 km from the epicenter. Our studies on characterization of local site conditions and seismic site amplification indicate that prevailing near-surface geological conditions in the Washington DC area played a major role in the unusually strong shaking experienced in this area. Current building code procedures for site characterization and development of design site amplification factors grossly underestimate the high frequency (greater than 1 Hz) ground motion amplifications that occur from moderate magnitude Central and Eastern United States (CEUS) earthquakes at sites in geological conditions typical of the Washington DC area. These conditions exist in many other major urban centers along the eastern seaboard. This presentation focuses on our data collection efforts, characterization of local site conditions across Washington DC and site response analyses to capture the seismic site amplification potential in the region. The data collection and characterization of local site conditions was coordinated with local engineering firms and gathered more than 500 sites in the region with geological, geotechnical and seismological profiles. The large data set was used to develop robust statistical models of the near-surface velocity versus depth profiles in Washington DC and nearby areas. Random field modeling was utilized to develop additional profiles where profile data was not available. This also allowed us to establish probabilistic descriptions of expected site response factors as a function of frequency. The results from this study will help us develop a procedure whereby this information can be systematically applied in simplified engineering design procedures.