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The application of the natural and social sciences
for the reduction of risk resulting from the effects of
earthquakes. Although earthquake shaking and building
collapse are the primary causes of loss of life and property,
earthquake loss can also be caused by other effects such as
ground failure (e.g., liquefaction, landsliding), tsunami, fire
and hazardous materials release, and is also caused by busi-
ness and social disruption, equipment and content damage,
and lifeline damage (Fig. 1). Lifelines are urban services, such
as water, power, gas, communications, and transportation,
without which an urban region cannot function. Occasionally,
effects other than shaking, such as widespread ground failure,
tsunami, fire following an earthquake, landslides, or release of
hazardous materials, may be the dominant agents of damage
in a particular earthquake.
Performance-based design
High-seismic regions, such as San Francisco or Tokyo, typically
experience a strong earthquake only once in many decades.
Because strong earthquakes are rare events, until recently,
building codes were based on allowing some significant degree
of damage. If a strong earthquake occurred, structures were
designed so that most would not collapse but might be dam-
aged, which resulted in significant costs for repairs, business
interruption, and, potentially, casualties. This degree of damage
was tolerated because tools for understanding and designing
Earthquake Engineering
Article by: Charles Scawthorn, SPA Risk LLC, Oakland, California.
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Key Concepts
• Earthquake engineers use information derived from seismic research to identify and mitigate structural risk
from future earthquake events.
• Earthquake engineering involves specific activities: seismic hazard quantification; structural and non-structural
(e.g., equipment) analysis, design, and/or retrofitting; and operational planning, in order to prevent disruption
due to earthquakes.
• Structural vulnerability is the expected damage from an earthquake given a specified hazard (such as fault rupture
or shaking), and is used to calculate the expected loss or seismic risk of the structure.
• The most seismically hazardous existing building structures are low-strength masonry, unreinforced brick masonry,
nonductile reinforced concrete, and certain kinds of precast concrete buildings. Earthquake engineers typically
mitigate vulnerability in such buildings by structural retrofitting.
• Current approaches to seismic design also include methods that modify the structural response to reduce earthquake loads,
such as base isolation, supplemental damping, and active control.
Fig. 1: Damage to reinforced-concrete frame buildings, M7.8 Gorkha, Nepal earthquake of
April 25, 2015.
(Credit: J. Bevington)
