2
Fig. 2 (a–c): Traditional earthquake force-resisting systems, and (d–f ) emerging technologies for earthquake
force-reducing systems.
Earthquake Engineering (continued)
+
ward
'
s
science
for highly nonlinear structural behavior
did not exist, and because of a rarely
examined belief that design for major
earthquake ground motions would be
prohibitively expensive. As a result, older
buildings are often seismically unsafe
and require retrofitting. At present,
performance-based design (PBD) is prac-
ticed, which consists of a comprehen-
sive approach to managing structural
performance to reduce seismic dam-
age to acceptable levels. PBD consists
of several steps, including (1) seismic
hazard identification and quantification,
(2) establishment of performance goals
for the structure, and (3) structural and
equipment analysis, design, or retrofit-
ting to achieve those goals. Using PBD,
earthquake engineers work closely with
emergency planners, social scientists,
and financial managers in an effort to
achieve resilience, which is the ability
to adapt to and rapidly recover from
hazards, shocks, or stresses without
compromising long-term prospects for
development. This is in recognition that
the damaging effects of earthquakes are
not reduced by a structural approach
alone, but require an integrated and
comprehensive program of facility and
organizational seismic review, analysis,
modification, emergency planning, and
risk transfer, drawing on the expertise of
mechanical engineers, operations spe-
cialists, social scientists, emergency plan-
ners, and insurers/finance specialists, in
addition to geoscientists and structural
engineers.
Hazards
Tectonic earthquakes, the typical cause
of major seismic disasters, are caused by
the fracture and sliding of portions of
the Earth's crust along faults, which may
be hundreds of kilometers long, from 1
to over 100 km deep, and sometimes not
readily apparent at the ground surface.
Earthquakes can occur anywhere on
Earth, but most often occur along major
tectonic plate boundaries, especially on
the circum-Pacific plate boundary (the
"Ring of Fire"), the Caribbean, and the
Trans-Alpide belt, the latter stretching
from southern France through the Medi-
terranean and the Middle East, along the
Himalayan foothills and the Indonesian
archipelago. In the United States, 39
of the 50 states are considered moder-
ate to high in seismic risk, with major
earthquake potential in Alaska, western
states, central states (St. Louis–Memphis
region), and portions of the East Coast
(South Carolina and Massachusetts).
Earthquakes can cause significant dam-
age to the built environment as a result
of fault rupture, vibratory ground motion
