For more than a century, Parsons Brinckerhoff (PB) has been instrumental in advancing state-of-the-art design and construction of underground structures, and the fields of seismic design and earthquake engineering are no exceptions. Almost three decades ago PB’s engineers pioneered in these fields in the design and construction of the San Francisco BART system, whose toughness during earthquakes, including the recent Loma Prieta event, has been amply tested. Recently, PB developed state-of-theart, two-level seismic design philosophy in its ongoing Los Angeles Metro and Boston Central Artery/Third Harbor Tunnel projects, taking into account both performance-level and life-safety-level earthquakes. This monograph represents PB’s continuous attempts in the seismic design and construction of underground structures to: a) Improve our understanding of seismic response of underground structures b)Formulate a consistent and rational seismic design procedure