The project will organize, convene and report on a workshop on the effects of the April 22, 1991 Costa Rica earthquake. This earthquake presents an unique opportunity to study the performance of structures sited on very soft and liquefiable soils. The workshop intends to study and identify analysis, retrofit, and design techniques to mitigate damage when poor soil conditions exist. It focuses on identifying areas where more research is needed and on recommending practical solutions for existing structures, with emphasis on lifelines (bridges, water and electrical systems, emergency services, and key industrial facilities). The results will be directly applicable to the U.S. practice since large areas of the U.S., including the San Francisco Bay Area, the Mississippi River Valley, and several East Coast seismic regions are potentially vulnerable to similar problems if subjected to strong ground shaking.