The branch of engineering concerned with reducing earthquake or seismic risk to structures. Because strong earthquakes are rare events, building codes have traditionally allowed a significant degree of damage. Even high-seismic regions, such as San Francisco or Tokyo, typically experience a strong earthquake only once in many decades. If an earthquake occurs, buildings and other structures are designed such that most will be damaged (but should not collapse), and will have costs for repairs, business interruption, and potentially casualties. While building collapse is the primary cause of loss of life in most earthquakes, other contributors to earthquake loss include equipment and contents damage, business interruption, and damage to lifelines, such as water, power, gas, communications, and transportation. To limit these losses to acceptable levels, earthquake engineering involves a process of (1) seismic hazard identification, (2) structural analysis, design, and/or retrofitting to prevent structural collapse and reduce property damage, and (3) review of equipment and operations to prevent disruption due to earthquakes—that is, an integrated, comprehensive program of facility seismic review, analysis, retrofit, emergency planning, and risk transfer, involving the expertise of mechanical engineers, operations specialists, emergency planners, and insurers, in addition to geoscientists and structural engineers.