Earthquakes are one of nature’s greatest hazards to life and property. Throughout historic times, they have caused the destruction of countless cities and villages around the world and infl icted the death of thousands of people (see Appendix). In the last 30 years alone, thousands of people were injured or lost their lives, and many more were left homeless, by earthquakes. The totally unexpected and nearly instantaneous devastation they may cause produces a unique psychological impact and a fear on modern societies that it is unsurpassed by any other natural hazard. This devastation, however, is owed almost entirely to the effect of earthquakes on civil engineering structures and the ground that supports them. It is the collapse of bridges, buildings, dams, and other structures that, together with the indirect effects of these collapses, causes extensive damage and loss of life during earthquakes. In principle, therefore, with the effective application of scientifi c and engineering principles and techniques, societies can minimize, if not completely eliminate, earthquake catastrophes.