Geo-Seismic Design in the Eastern United States: State of Practice

A moderate earthquake in the Eastern United States (US) could affect millions of people and potentially impact the world economy. The region is home to many densely populated urban centers, including the nation's capital, Washington, DC, and the financial capital of the world, New York City. The anticipated moderate earthquake hazard places the region at high seismic risk because a significant portion of the infrastructure, including buildings, bridges, and public utilities, were not designed to accommodate seismic loading. Eastern US practice of geo-seismic engineering has a relatively short history. We will discuss engineering approaches presently followed to address common geo-seismic problems such as seismic hazard assessment, site response analysis, and liquefaction potential evaluation. Most of these approaches are based on developments and experiences from the Western US and other seismically active areas. Certain concepts and requirements from the seismically active areas may not be applicable due to unique geological and tectonic characteristics of the Eastern US such as: (i) very hard bedrock; (ii) sparse strong motion data; and (iii) unique regional geology of overburden soils. These unique characteristics affect geo-seismic analyses due to the high impedance contrast between the relatively soft overburden soils and stiff bedrock, and the vibrational differences between the predicted high-frequency bedrock motions and low-frequency deep soft sites. We will present an overview of the geology and regional aspects of geo-seismic design with some practical examples.